[Repeater-Builder] Re: tx combiner follow up... UPDATE 2-E (not 2-Z)
> "vintageaudio2004" <[EMAIL PROTECTED]> wrote: > > The above is a bpbr duplexer, not a pre-selector. You > No, the TPCP-1546C is a preselector, take a look: > http://www.telewave.com/pdf/TWDS-2006.pdf > I think you are confused with the TPRD-1546C which is > indeed a duplexer. Actually what pops up is how you access Telewaves web page from google or how they cross part numbers. No biggie, we're both on the same page now. > I must have been reading your mind. Yesterday I was going > again over the specs of the TPCP-1546C, and came across > that "C" which stands for [Compact]. So I though that since > we really don't have much of in a way of size constrains, > why possibly put compact size ahead of better performance, > and found the TCPC-1556 which is a full size cavity > Preselector. Compact used to mean less performance... but everyone is getting really good at squeezing high specs out of smaller bottles. If you have enough Q, you have enough... > So basically we still would rather go one step at a time, > not that I want to dismiss your great advise, or don't > fully appreciate and now also understand your suggestions, > but since this way we are going to be able to apply each > solution at a time, that would enable us to re-evaluate > the system, determine how far it improved, and then decide > if we need additional filtering, by also taking into account > our customers real needs. Not that I would not love to buy > all the stuff at once and get it over with, and I would > also be very happy if this system could be honed to absolute > perfection. I understand... when I'm not footing the bill, I'll also be happy to suggest a full size hot tub for the installers. :-) > Another important consideration is that we also need to put > our feet on the ground in respect to the price tags of the > added filtering, I was about to offer up that you include an expresso bar at the site. Won't do much for the radio system but you'd work a lot faster. > so going in steps seems also to be the right decision in that > angle. Don't really want to add it up unless it would be > strictly required, as any additional expenses, unforeseen as > they may have been, will in this case have to come out of our > own pockets. Bingo... > As of now I just placed an order for the TCPC-1556, and asked > them to close the window to narrowly just let pass our Rx > range, and put maximum rejection on the Tx range. Also to make > the skirts as steep as it be practically possible, even if > insertion losses grow to 3-4dB, or maybe even a bit more. Coping > with them on the Rx side should be relatively painless, easy > to compensate, and as you pointed out earlier, well worth. I'll > keep you posted of any new developments. The TCPC unit might be enough... > Have a great day, and thanks again for your excellent advise. > > Saludos, > Alex Let us know how things work out Alex. cheers, skipp skipp025 at yahoo.com www.radiowrench.com Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2-D (not 3-D)
--- In Repeater-Builder@yahoogroups.com, "skipp025" <[EMAIL PROTECTED]> wrote:
> > "vintageaudio2004" <[EMAIL PROTECTED]> wrote:
> > as a first step we will be ordering the Telewave
> > TPCP-1546C preselector, it has 6 cavities and has a pretty
> > good looking skirt (-80db @ 4MHz down).
>
> The above is a bpbr duplexer, not a pre-selector. You
> can easily special order it as a pre-selector, but you'd
> better understand what you need to have in the receive
> side pre-selection. You need both a window filter with
> tight skirts and a quality notch function. Getting it to
> play in one package is possible, but tricky to do it right.
No, the TPCP-1546C is a preselector, take a look:
http://www.telewave.com/pdf/TWDS-2006.pdf
I think you are confused with the TPRD-1546C which is indeed a duplexer.
> > Additionally wanted to order a Lo-Pass filter to put at
> > the output of the Tx combiner, as a "just in case".
> > How 'bout a Telewave TLF-150 ?
>
> Sure, but it's "a pop-corn fart" and won't do much for
> you. I'd actually be more worried about it in series with
> all the tx power. It becomes a weak link in the TX side
> when you have reflected power problems.
OK got it. It's out.
> > > ("these are not the Droids you're looking for... move along")
> > Aaaah, Star Wars fan. Me too, but not so much of the later
episodes. Nothing like the first one (was it "Episode IV" ?).
>
> A casual fan... not much more. But the line is pretty funny.
Yeah, me too, but since you remembered that line, I tought you might
probably be a bit more of a fan than you think you are.
> Go with Telewave... just order what's going to work right. I
> like and use tons of Telewave goodies.
> > > But remember your final tx and rx antenna systems should include
> > > some notch cavities. Telewave makes good notch cavities and
> > > they should be able to offer coax T options, which lean the
> > > series cavity response over.
I must have been reading your mind. Yesterday I was going again over
the specs of the TPCP-1546C, and came across that "C" which stands for
[Compact]. So I though that since we really don't have much of in a
way of size constrains, why possibly put compact size ahead of better
performance, and found the TCPC-1556 which is a full size cavity
Preselector.
So basically we still would rather go one step at a time, not that I
want to dismiss your great advise, or don't fully appreciate and now
also understand your suggestions, but since this way we are going to
be able to apply each solution at a time, that would enable us to
re-evaluate the system, determine how far it improved, and then decide
if we need additional filtering, by also taking into account our
customers real needs. Not that I would not love to buy all the stuff
at once and get it over with, and I would also be very happy if this
system could be honed to absolute perfection.
BTW since you mentioned portable performance of the system, these are
only going to be used close to the site, maybe 1-3 miles away tops,
and most other operations will use mobile 25W units (GM660's) with 3/4
wave antennas. The system requirements originally submitted by the
customer only called for a 12-15 mile radius, and that with mobile
units. Thick vegetation with lots of humidity, and some low hills and
terrain depressions where at that time our main consideration. On the
other hand for the same price we got them much more range (no way
where we going to use any other repeater besides a 100W MTR2000). The
added range made them very happy, as sometimes they must travel
outside of the working areas and any additional communications range
is very valuable in such remote areas in case of emergencies, or
whatever else calls they might need to place.
Another important consideration is that we also need to put our feet
on the ground in respect to the price tags of the added filtering, so
going in steps seems also to be the right decision in that angle.
Don't really want to add it up unless it would be strictly required,
as any additional expenses, unforeseen as they may have been, will in
this case have to come out of our own pockets.
As of now I just placed an order for the TCPC-1556, and asked them to
close the window to narrowly just let pass our Rx range, and put
maximum rejection on the Tx range. Also to make the skirts as steep as
it be practically possible, even if insertion losses grow to 3-4dB, or
maybe even a bit more. Coping with them on the Rx side should be
relatively painless, easy to compensate, and as you pointed out
earlier, well worth. I'll keep you posted of any new developments.
Have a great day, and thanks again for your excellent advise.
Saludos,
Alex
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[Repeater-Builder] Re: tx combiner follow up... UPDATE 2-D (not 3-D)
> "vintageaudio2004" <[EMAIL PROTECTED]> wrote:
> Took the weekend off, needed to get away from this
> stuff for a while, was starting to get dizzy with
> so much info coming and going all over.
We understand... did the same thing here.
> We decided to go in steps and see if things work out, and
> if needed, go back and add some more filtering. After
> comparing some factors (DCI vs. Telewave, delivery time +
> specs) as a first step we will be ordering the Telewave
> TPCP-1546C preselector, it has 6 cavities and has a pretty
> good looking skirt (-80db @ 4MHz down).
The above is a bpbr duplexer, not a pre-selector. You
can easily special order it as a pre-selector, but you'd
better understand what you need to have in the receive
side pre-selection. You need both a window filter with
tight skirts and a quality notch function. Getting it to
play in one package is possible, but tricky to do it right.
> Also wanted to order a 4-pole TX window filter from DCI
> but their 4 week delivery time will not allow us to take
> it with us on this trip (in about 2 weeks time), so we'll
> see how things go with just the preselector and if needed
> would order additional stuff from DCI. Still nothing written
> in stone, also would give consideration to your notch
> filter suggestion.
Better give more than consideration if you really want the
system to work really well.
> Additionally wanted to order a Lo-Pass filter to put at
> the output of the Tx combiner, as a "just in case". At
> least take it with us, try it, and if there is no difference
> then leave it out, maybe use another day somewhere else.
> It's a long way to the site, and it would not cost
> much to order it. How 'bout a Telewave TLF-150 ?
Sure, but it's "a pop-corn fart" and won't do much for
you. I'd actually be more worried about it in series with
all the tx power. It becomes a weak link in the TX side
when you have reflected power problems.
> In any case I guess it makes not much sense to leave
> in the original preselector anyway.
can't fight a house fire with a garden hose...
> > I would not put a window filter on the tx side, but you
> > could if you want. I would put notch filters in both tx
> > and rx paths.
> So could you possibly suggest the notch cavities that
> you would choose in this case, by brand and model? Maybe
> the Telewave TWNC-150x series? What diameter would you
> suggest (they come in 5, 8 and 10").
Have Telewave spec you a min 4, better 6 cavity series notch
cavity system on vhf. For the tx side... center the notch window
in the receiver frequency window. For the RX side... center
the notch window in the transmit frequency window.
In short, order two notch cavity systems (networks), one
for tx, the other for the rx side.
The key is to remember the desired signals in the path. Have
the notch network spec'd so it notches the reject side, but
has the slope of the desired pass side altered (most often
with coax stubs or a reactance in series with the T to notch
cavity path) to provide a higher "pass shoulder". Telewave
should easily know how to do this using their method of choice.
> > The above mentioned Telewave filter is not what you need.
>
> Pardon my asking, but why are you so sure it won't work?
> Have you seen the skirts of this preselector? Looks very
> close to 80db down at 4 MHz off center, where our Tx
> carriers are located.
Let me clarify what I meant... won't work as built... read on.
> Since it is supposed to have a 2.5MHz window, whe were going
> to ask Telewave to reduce it to just over 1MHz, and "dial up"
> the skirts as much as possible within practical limits. As a
> matter of fact the Telewave 6-cavity preselector "stock"
> skirts look quite similar (to me / on paper anyway) to the
> 8-pole DCI filter. Anyway, just how much rejection you reckon
> we need then, more than 90 or more db's?
Now you're cooking... or at least on the right track. Both the
DCI and Telewave units will work, but their out of the box
stock versions will not work to solve your problems.
> > ("these are not the Droids you're looking for... move along")
> Aaaah, Star Wars fan. Me too, but not so much of the later episodes.
> Nothing like the first one (was it "Episode IV" ?).
A casual fan... not much more. But the line is pretty funny.
> > > Telewave (posted their full response at the bottom) suggested
> > > the TPCP-1544C Preselector, but it seems we could only expect
> > > 45-50db isolation with that one. A bit tight, if adequate at
> > > all in this case. http://www.telewave.com/pdf/TWDS-2005.pdf
Not nearly enough protection...
> > Nothing wrong with the tx part Telewave sold you... by patching
> > in a fix on the as-built rx side is not really a workable
> > solution at this time.
>
> Again sorry I have to ask, but why not? Please if you could
> elaborate a bit more... It's just that those 80db rejection
> at 4MHz off-center that th
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2-B or not 2-B, so 2-C
Hi Skipp,
Took the weekend off, needed to get away from this stuff for a while,
was starting to get dizzy with so much info coming and going all over.
--- In Repeater-Builder@yahoogroups.com, "skipp025" <[EMAIL PROTECTED]> wrote:
>
> You should not be thinking less than 8 poles, maybe even
> more and don't forget the notch filters I mentioned in
> both the tx and rx paths.
We decided to go in steps and see if things work out, and if needed,
go back and add some more filtering. After comparing some factors (DCI
vs. Telewave, delivery time + specs) as a first step we will be
ordering the Telewave TPCP-1546C preselector, it has 6 cavities and
has a pretty good looking skirt (-80db @ 4MHz down). Also wanted to
order a 4-pole TX window filter from DCI but their 4 week delivery
time will not allow us to take it with us on this trip (in about 2
weeks time), so we'll see how things go with just the preselector and
if needed would order additional stuff from DCI. Still nothing written
in stone, also would give consideration to your notch filter suggestion.
Additionally wanted to order a Lo-Pass filter to put at the output of
the Tx combiner, as a "just in case". At least take it with us, try
it, and if there is no difference then leave it out, maybe use another
day somewhere else. It's a long way to the site, and it would not cost
much to order it. How 'bout a Telewave TLF-150 ?
>
> You could (and I would) dial up the skirts on the filter,
> which also increase the insertion loss. Don't fret 1.8 to
> 3 dB insertion loss if it cures your problem and makes the
> system work. You have monster antenna gain anyway.
Tailoring the response is one of the things I wanted to discuss with
Ralph but I haven't heard back from him since I wrote him this morning.
>
> Park (remove from the path) the 2 dB pad, the original
> Sinclair pre-selector unit and possibly the preamp. Depending
> on the specific preamp model type, you might want to replace
> it with something that has more IM3 protection and/or
> less noise.
Will do that, probably step by step and testing after removing each
component to get a feel of any changes. In any case I guess it makes
not much sense to leave in the original preselector anyway.
>
> I mentioned I'm not fond of Chips VHF Preamps simply because
> they are bipolar type (higher noise). He says Phempts and
> GasFets aren't worth the money... I say they are and I mostly
> use them in my vhf systems. Check the noise figure on the
> bipolar preamp models, that should be enough to convince
> you the Phempt or GasFet is worth using at VHF. Much
> of the choice depends on location and the noise floor, but
> I like to go with a winner right out of the staring gate.
I agree with you. If a better (and more expensive) preamp gives you a
better performance, solves a problem, or provides peace of mind for
future site requirements, than spending some extra dollars is
definitively worth every penny.
> I would not put a window filter on the tx side, but you
> could if you want. I would put notch filters in both tx
> and rx paths.
So could you possibly suggest the notch cavities that you would choose
in this case, by brand and model? Maybe the Telewave TWNC-150x series?
What diameter would you suggest (they come in 5, 8 and 10").
> Get over the higher insertion loss issue, it's not that much
> in the real world and you're probably going to end up with
> that much in the DCI and notch filter path for the receiver.
Not really concerned with that, specially in the RX path where one can
make up for it rather easily.
> If I spec'd the above example DCI filter for a system I
> was doing, I have them really tighten up the skirts (per
> my specific needs), which would increase the insertion
> loss near or above 2 dB. Sean was nice enough to run
> some preformance tests on the last 3 UHF 10 pole Window
> Filters they made for me. I had a chance to juggle the
> numbers before the final choices were locked down.
>
> There is a preformance point (on the graph) where you
> trade a little insertion loss for a lot of protection.
> You can easily live with a few dB of insertion loss
> but you can't work without the required protection.
>
> The above mentioned Telewave filter is not what you need.
Pardon my asking, but why are you so sure it won't work? Have you seen
the skirts of this preselector? Looks very close to 80db down at 4 MHz
off center, where our Tx carriers are located. Since it is supposed to
have a 2.5MHz window, whe were going to ask Telewave to reduce it to
just over 1MHz, and "dial up" the skirts as much as possible within
practical limits. As a matter of fact the Telewave 6-cavity
preselector "stock" skirts look quite similar (to me / on paper
anyway) to the 8-pole DCI filter. Anyway, just how much rejection you
reckon we need then, more than 90 or more db's?
> ("these are not the Droids you're looking for... move along")
Aaaah, Star Wars fan. Me too, but n
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2-B or not 2-B, so 2-C
> "vintageaudio2004" <[EMAIL PROTECTED]> wrote:
> Ralph from DCI suggested either a 4-pole or an 8-pole
> filter. Here's a link he sent, and I must say that it
> looks pretty good.
> http://www.dci.ca/html_commercial/graph_158-4-8_wo219.htm
You should not be thinking less than 8 poles, maybe even
more and don't forget the notch filters I mentioned in
both the tx and rx paths.
> only 1db insertion loss. Price is quite reasonable, only
> delivery of 4 weeks (or maybe less), is a bit of a problem
> as we ideally would need to return to the site in about
> two weeks time.
You could (and I would) dial up the skirts on the filter,
which also increase the insertion loss. Don't fret 1.8 to
3 dB insertion loss if it cures your problem and makes the
system work. You have monster antenna gain anyway.
> In regards to the added insertion loss of 1db of the filter,
> to compensate for this maybe we could probably bypass the
> stock Preselector that came with the multicoupler, and/or
> just remove a 2db pad that is now installed between the
> output of the multicoupler preamplifier and the power divider.
> Would you say this is a viable option?
Park (remove from the path) the 2 dB pad, the original
Sinclair pre-selector unit and possibly the preamp. Depending
on the specific preamp model type, you might want to replace
it with something that has more IM3 protection and/or
less noise.
I mentioned I'm not fond of Chips VHF Preamps simply because
they are bipolar type (higher noise). He says Phempts and
GasFets aren't worth the money... I say they are and I mostly
use them in my vhf systems. Check the noise figure on the
bipolar preamp models, that should be enough to convince
you the Phempt or GasFet is worth using at VHF. Much
of the choice depends on location and the noise floor, but
I like to go with a winner right out of the staring gate.
Chip Angle makes great stuff, I use his UHF Preamps quite
a bit, but at VHF I use my own Phempt design or an ARR
(or other brand, same type) GasFet.
> Using the 8-pole might probably seem like a bit of overkill,
> but given the critical need to not only solve the problem,
> plus the difficult access (it's very distant) to the site
> where the system is installed, we would like to have the peace
> of mind of an additional margin of safety. For this reason
> maybe we might also consider filtering the TX path as well,
> also with another 8-pole filter, or maybe just 4-poles.
The DCI 8 pole size filter is a min must use size... maybe
more in problematic systems. You really need the protection.
I would not put a window filter on the tx side, but you
could if you want. I would put notch filters in both tx
and rx paths.
> The only other Preselector option that we are considering
> at the moment is the Telewave TPCP-1546C 6-cavity Preselector,
> as it seems to offer between -70 to -80db isolation at
> 4-5MHz off center, although we don't like much the 2.5db
> added insertion loss. If you care to take a
> look at it, the datasheet is here:
> http://www.telewave.com/pdf/TWDS-2006.pdf
Get over the higher insertion loss issue, it's not that much
in the real world and you're probably going to end up with
that much in the DCI and notch filter path for the receiver.
If I spec'd the above example DCI filter for a system I
was doing, I have them really tighten up the skirts (per
my specific needs), which would increase the insertion
loss near or above 2 dB. Sean was nice enough to run
some preformance tests on the last 3 UHF 10 pole Window
Filters they made for me. I had a chance to juggle the
numbers before the final choices were locked down.
There is a preformance point (on the graph) where you
trade a little insertion loss for a lot of protection.
You can easily live with a few dB of insertion loss
but you can't work without the required protection.
The above mentioned Telewave filter is not what you need.
("these are not the Droids you're looking for... move along")
> Telewave (posted their full response at the bottom) suggested the
> TPCP-1544C Preselector, but it seems we could only expect 45-50db
> isolation with that one. A bit tight, if adequate at all in this
> case. http://www.telewave.com/pdf/TWDS-2005.pdf
Nothing wrong with the tx part Telewave sold you... by patching
in a fix on the as-built rx side is not really a workable
solution at this time.
> > My VHF rx pre-selection system is a very special network made
> > for use with non-sequencial (mixed spaced) receiver inputs. Oh
> > the joy it was to make...
>
> I can imagine it was a bit of a pain to make, but glad to hear is
> humming along nicely now. both your positive comments on DCI, and
> their prompt and helpfull responses actually made me want to include
> them in our short list of possible solution providers. You might be
> able to ask for a possible sales commission... ;-)
I want DCI to stay in business so I can buy more filters from
Re: [Repeater-Builder] Re: tx combiner follow up... UPDATE 2-B
At 8/12/2005 08:57 AM, you wrote: >I can imagine it was a bit of a pain to make, but glad to hear is >humming along nicely now. both your positive comments on DCI, and >their prompt and helpfull responses actually made me want to include >them in our short list of possible solution providers. You might be >able to ask for a possible sales commission... ;-) I like DCI's products, but I wish their quality control was a bit better. We had to do field repair on one of their 2 meter BPFs because one of the SO-239 connectors was loose because the mounting screws were stripped. Had to take out every one of those weird-headed screws holding the top plate to get inside. Bob NO6B Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2
--- In Repeater-Builder@yahoogroups.com, Kris Kirby <[EMAIL PROTECTED]> wrote: > http://www.google.com/search?as_q=&num=10&hl=en&btnG=Google+Search&as_epq=&as_oq=&as_eq=&lr=&as_ft=i&as_filetype=pdf&as_qdr=all&as_occt=any&as_dt=i&as_sitesearch=motorola.com&safe=images > > Just add the word you want to that query and stuff comes out of the > woodwork. Hi Kris, Thanks for the tip. Excellent way to get specific info by using google. Alex Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2-B
--- In Repeater-Builder@yahoogroups.com, "skipp025" <[EMAIL PROTECTED]> wrote: I've had DCI make a number of repeater window filters for me. > > It took a bit of time on the phone with Sean to find out what > they could do vs what trade offs I would allow in the specs. > The end result UHF 10 pole filters they made to my specs work > just killer. VHF is another animal... Ralph from DCI suggested either a 4-pole or an 8-pole filter. Here's a link he sent, and I must say that it looks pretty good. http://www.dci.ca/html_commercial/graph_158-4-8_wo219.htm >From that I gather from the response curve of the 8-pole unit, we could then expect to get something in the order of -90db (or more?) isolation at 4MHz off-center (where our Tx carriers are located), with only 1db insertion loss. Price is quite reasonable, only delivery of 4 weeks (or maybe less), is a bit of a problem as we ideally would need to return to the site in about two weeks time. In regards to the added insertion loss of 1db of the filter, to compensate for this maybe we could probably bypass the stock Preselector that came with the multicoupler, and/or just remove a 2db pad that is now installed between the output of the multicoupler preamplifier and the power divider. Would you say this is a viable option? Using the 8-pole might probably seem like a bit of overkill, but given the critical need to not only solve the problem, plus the difficult access (it's very distant) to the site where the system is installed, we would like to have the peace of mind of an additional margin of safety. For this reason maybe we might also consider filtering the TX path as well, also with another 8-pole filter, or maybe just 4-poles. The only other Preselector option that we are considering at the moment is the Telewave TPCP-1546C 6-cavity Preselector, as it seems to offer between -70 to -80db isolation at 4-5MHz off center, although we don't like much the 2.5db added insertion loss. If you care to take a look at it, the datasheet is here: http://www.telewave.com/pdf/TWDS-2006.pdf Telewave (posted their full response at the bottom) suggested the TPCP-1544C Preselector, but it seems we could only expect 45-50db isolation with that one. A bit tight, if adequate at all in this case. http://www.telewave.com/pdf/TWDS-2005.pdf > > I've taken a look at the DCI site, and also contacted them. They > > promptly responded and seemed very eager to help. Have you had any > > previous experience with their products and so forth? > > Excellente' you will luck out by having all your receivers > within a same window. Imagine doing receive preselection when > the FCC gives you "pop-corn picked receiver input frequencies". > > My VHF rx pre-selection system is a very special network made > for use with non-sequencial (mixed spaced) receiver inputs. Oh > the joy it was to make... I can imagine it was a bit of a pain to make, but glad to hear is humming along nicely now. both your positive comments on DCI, and their prompt and helpfull responses actually made me want to include them in our short list of possible solution providers. You might be able to ask for a possible sales commission... ;-) > You don't mention if the system will be mostly mobile or > combo mobile and portable operation. If you don't have any > portables, bypass the preamp right away... you don't really > even need it at this point in the game. It has to handle both portables and mobiles, although portables will only be used for close range communication well within view of the tower (2-5 miles). Still as it is, portables have been proven to be still usable further away, but for reliable communications they will have to use the mobile radios, as the very dense vegetation around the site, plus the mostly small winding roads that where cut between small hills have proven to be a big factor in attenuating RF signals. On the open we managed to place a reliable call from about 30 something miles away. Probably still good for another 10-15 miles, but with some gray areas. > There's a really killer Dubus Magazine Phempt Preamp > article available for free on my www.radiowrench.com/sonic > web page, which well describes some of the problems with > preamps and example noise floor levels of a location. Well > worth a look if you have time... Yesterday I downloaded the PDF, but didn't have a chance to read it. Indeed it looks like a real killer preamp. > Some of us only dream of a low noise floor... but then there's > that city of 1.2 million just down the mountain and that [EMAIL PROTECTED] > military radar and eplers system nearby. I hear you. We have that problem here in Caracas. VHF is basically so congested that it is almost unusable at any of the good mountain top sites. BTW, yesterday the Telewave response came in. See bellow. Well its about lunch time, at least around these parts. Bon Apetit eveyone, specially you Skipp. We also take our lunches VERY seriously. :-)) Alex
Re: [Repeater-Builder] Re: tx combiner follow up... UPDATE 2
On Thu, 11 Aug 2005, vintageaudio2004 wrote: > Thanks for the excellent explanation. It would be nice to be able to > have a look at some of those /\/\ white papers. http://www.google.com/search?as_q=&num=10&hl=en&btnG=Google+Search&as_epq=&as_oq=&as_eq=&lr=&as_ft=i&as_filetype=pdf&as_qdr=all&as_occt=any&as_dt=i&as_sitesearch=motorola.com&safe=images Just add the word you want to that query and stuff comes out of the woodwork. -- Kris Kirby <[EMAIL PROTECTED]> "BIG BROTHER IS WATCHING YOU!" This message brought to you by the US Department of Homeland Security and the now-permanent PATRIOT Act Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2-B
> "vintageaudio2004" <[EMAIL PROTECTED]> wrote: > Hi, > Thank you very much for you very detailed explanations. > They are very helpful. Bellow please find some responses > to your message. Believe it or not, some of us live for this stuff. > > "nj902" <[EMAIL PROTECTED]> wrote: > > As Skipp indicated - your Sinclair RX preselector is less > > than optimum. If you look at the filter's curve on the > > Sinclair web site you will see that your transmitter > > frequencies are only being attenuated by about 25 dB. Not nearly enough > > There are many 'window' filters available with steeper > > skirts, for example, look at this DCI filter: > > http://www.dci.ca/html_commercial/graph_165d92-1-6_wo143.htm I've had DCI make a number of repeater window filters for me. It took a bit of time on the phone with Sean to find out what they could do vs what trade offs I would allow in the specs. The end result UHF 10 pole filters they made to my specs work just killer. VHF is another animal... > I've taken a look at the DCI site, and also contacted them. They > promptly responded and seemed very eager to help. Have you had any > previous experience with their products and so forth? Excellente' you will luck out by having all your receivers within a same window. Imagine doing receive preselection when the FCC gives you "pop-corn picked receiver input frequencies". My VHF rx pre-selection system is a very special network made for use with non-sequencial (mixed spaced) receiver inputs. Oh the joy it was to make... > > If we allow the system IM point to be degraded - then > > strong receive signals from our own close-in mobiles > > and control stations become a very real problem. Motorola > > has several white papers that warn > > System Engineers of this issue. > Thanks for the excellent explanation. It would be nice to > be able to have a look at some of those /\/\ white papers. The root of the problem is the engineering... Larger companies don't want to keep higher paid Engineers on staff and smaller radio shops can't afford them. It would be really nice to have access to the mentioned white papers. > > > It is not clear from your system description if you replaced the > > Sinclair amp with the Anglelinear amp - or - if both are in line. Sinclair supplies some of their equipment with Angle Linear preamps. Good stuff, but it's probably also bi-polar at VHF. might want to check that... > No, the Anglelinear came with the multicoupler. As it is now, the > multicoupler is still completely stock, no modifications or > adjustments have been done to it. Even the 2dB pad came originally > with the unit. You don't mention if the system will be mostly mobile or combo mobile and portable operation. If you don't have any portables, bypass the preamp right away... you don't really even need it at this point in the game. > > To get the receive design right - you should start by > > measuring the site noise floor. Directly measuring site > > noise is a complex subject but for starters why not just > > test one MTR station directly on the recevie antenna. Square one along with desense and effective receiver sens. There's a really killer Dubus Magazine Phempt Preamp article available for free on my www.radiowrench.com/sonic web page, which well describes some of the problems with preamps and example noise floor levels of a location. Well worth a look if you have time... > Will do that when we return to the site to redo the present > grounding system, and hopefully resolve the IM issue. Although > I need to point out, this area being very remote, and scarcely > populated, I expect that the noise floor, even in VHF will be > much lower than average. Terrain is mostly flat, with lot's of > vegetation towards certain areas (tall trees, a few smaller > elevations, etc). Still we will measure the noise floor as > described just to be sure, and have the numbers at hand. Some of us only dream of a low noise floor... but then there's that city of 1.2 million just down the mountain and that [EMAIL PROTECTED] military radar and eplers system nearby. > BTW, yesterday I received a response from Sinclair, the multicoupler > vendor. They ran (another) IM study, and also indicated that they > believe that we have an "External IM Problem". The data we sent them > was exactly the same as we posted here on the group (system > description, tests, etc). It strikes me that no one else has so far > arrived at the same conclusion. For the benefit of the group, bellow > I've taken the liberty to copy the message text as it was received. Sinclair is probably right, but they should also have told you the bandpass filter is not nearly enough protection if you ran a system description by them before you bought the pre-selector assembly. > Still waiting for Telewave's response (the combiner vendor). > Thanks again for all your help. > Alex > Lunch was good... cheers, skip
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2
Hi, Thank you very much for you very detailed explanations. They are very helpful. Bellow please find some responses to your message. --- In Repeater-Builder@yahoogroups.com, "nj902" <[EMAIL PROTECTED]> wrote: > --- In Repeater-Builder@yahoogroups.com, "vintageaudio2004" > <[EMAIL PROTECTED]> wrote: As Skipp indicated - your Sinclair RX preselector is less than > optimum. If you look at the filter's curve on the Sinclair web site > you will see that your transmitter frequencies are only being > attenuated by about 25 dB. There are many 'window' filters available > with steeper skirts, for example, look at this DCI filter: > > http://www.dci.ca/html_commercial/graph_165d92-1-6_wo143.htm I've taken a look at the DCI site, and also contacted them. They promptly responded and seemed very eager to help. Have you had any previous experience with their products and so forth? > If we allow the system IM point to be degraded - then strong receive > signals from our own close-in mobiles and control stations become a > very real problem. Motorola has several white papers that warn > System Engineers of this issue. Thanks for the excellent explanation. It would be nice to be able to have a look at some of those /\/\ white papers. > It is not clear from your system description if you replaced the > Sinclair amp with the Anglelinear amp - or - if both are in line. No, the Anglelinear came with the multicoupler. As it is now, the multicoupler is still completely stock, no modifications or adjustments have been done to it. Even the 2dB pad came originally with the unit. > To get the receive design right - you should start by measuring the > site noise floor. Directly measuring site noise is a complex > subject but for starters why not just test one MTR station directly > on the recevie antenna. Will do that when we return to the site to redo the present grounding system, and hopefully resolve the IM issue. Although I need to point out, this area being very remote, and scarcely populated, I expect that the noise floor, even in VHF will be much lower than average. Terrain is mostly flat, with lot's of vegetation towards certain areas (tall trees, a few smaller elevations, etc). Still we will measure the noise floor as described just to be sure, and have the numbers at hand. BTW, yesterday I received a response from Sinclair, the multicoupler vendor. They ran (another) IM study, and also indicated that they believe that we have an "External IM Problem". The data we sent them was exactly the same as we posted here on the group (system description, tests, etc). It strikes me that no one else has so far arrived at the same conclusion. For the benefit of the group, bellow I've taken the liberty to copy the message text as it was received. Still waiting for Telewave's response (the combiner vendor). Thanks again for all your help. Alex I have attached copies of some IM study results. The system frequencies produce direct IM product hits starting at 9th order as shown in study titled AlexR. 11th is the highest the study can show, but it is likely they continue with higher odd multiples as well. A single antenna solution is not recommended due to the presence of these products. Check and see if these are the subtle products that you are hearing. Under normal circumstances with a tower in good condition and decent T-R antenna space isolation, I would not expect that you would have a problem with these higher order IM products. Adding any portable Tx frequency to the study will cause multiple direct A + B - C product hits due to the 5 MHz offset, as shown by AlexR+portable. I believe that you have an external IM problem. The mobile Rx antenna connected to the power divider with no amplification still detected the interference, which indicates an external mix that is coming in on the Rx frequencies. Also strong enough to cause a problem despite the splitter loss that is experienced by the signal without benefit of the LNA. A participating Tx carrier would encounter this split loss and the resulting IM level would be substantially reduced if the IM was occurring in the receiver itself. Diverting Tx power to a dummy load, prevents the RF currents from being induced in the tower or antenna network where the mix is being produced and then radiated to the Rx antenna in turn passing through (on frequency) the multicoupler to the receivers. Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2
Hi Milt, Thank you very much for your comets and suggestions, they are very apreciated. So as to save group bandwidth, Kindly please see my reply to Skipp's message, as it also deals with the antennas. http://groups.yahoo.com/group/Repeater-Builder/message/53034 Alex --- In Repeater-Builder@yahoogroups.com, "Ellen Engle" <[EMAIL PROTECTED]> wrote: The DB-228 is about 41 feet long. Top antenna cannot be fully top mounted due to it's size so that means that about 20 ft is side mounted. That puts the bottom of the TX antenna at 70 ft. >TX is mounted from about mid-tower down.< OK I am interperating this to mean that the top of the bottom antenna is at say 50 ft, which puts the bottom at 10 ft.Total antenna seperation 20 ft. or less. Big problem. > > When you purchased the system, was it engineered for this spacing or did the antenna system come later? > > You need more isolation between the antennas. I would strongly suggest that you replace the antennas with DB-224's (20 ft long). Aim for a minimum of 60 ft of space between the bottom of the top antenna and the top of the side mount antenna. Since the description of the DB-228 indicates that it is made of 2 DB-224E's it may be possible to simply split one of the antennas apart and test that way. > > If you must stay with these high gain antennas then your TX combining and RX distribution systems need to be reengineered taking into account the short spacing (low isolation) between the TX and RX antennas. > > Ditch the RG-58 and the 9913 and use RG-214 or Superflex for jumpers. > > Verify the tuning of the cavities. Things change in shipment, especially in rough terrain. > > > Milt Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2
--- In Repeater-Builder@yahoogroups.com, "vintageaudio2004" <[EMAIL PROTECTED]> wrote: "...SYSTEM DESCRIPTION ...Just as a refresher... ... a Sinclair RM201-112S1B RX Multicoupler fitted with a BP Preselector (with 1MHz pass-band, and factory tuned to 165.625), a "Hi Level" Bipolar preamp(Angle Linear brand / anglelinear.com), and a 12 port power divider. Between the preamp output and the power divider there is a 2dB pad fitted. _ You have certainly put a lot of effort into your investigation. I think you are on the right track to focus on the receive side of the system. As Skipp indicated - your Sinclair RX preselector is less than optimum. If you look at the filter's curve on the Sinclair web site you will see that your transmitter frequencies are only being attenuated by about 25 dB. There are many 'window' filters available with steeper skirts, for example, look at this DCI filter: http://www.dci.ca/html_commercial/graph_165d92-1-6_wo143.htm You indicated that you see the interference most often when a user radio is transmitting at the site - near the equipment or 3-400 feet away. This points us in a new direction. When an IM run is computed, normally the objective is to look for tx to tx mixes. Accordingly, the system transmit[and other co-located transmitter] frequencies are input as 'originators' and the system receive frequencies are input as 'targets'. However, if the IM is occurring in the receive side, your mobile tx [base receive] frequencies also need to be input as 'originators'. Now you get a LOT of hits. The problem is to understand the IM characteristics of your receiving system - system meaning the combination of all the elements - the base station receivers, the preselector, preamp, attenuator(s), power dividers, cable loss, etc. Your MTR2000 stations have an IM specification of 85 dB. Suppose we say your receive threshold is -116 dBm [0.35uv] What the IM spec means is that signals 85 dB stronger than -116 [-31] have the potential to mix and generate interference [assuming the mathematical mix is proper,e.g. 2A-B] But - your receiving system consists of more than just the MTR. The receiver filter, multicoupler, and preamp contribute to the equation. The preamp an particular. The primary use of the preamp is to overcome the loss of the power dividers. At UHF and 800 [where site noise is usually not a factor] we also take advantage of the preamp's low noise figure to improve the overall receiver system sensitivity. The unfortunate fact is that this improvement comes at a cost - that being the degradation of the receiving system IM rejection capability. For this reason - it is imperative that receiver preamp systems be carefully designed. If we allow the system IM point to be degraded - then strong receive signals from our own close-in mobiles and control stations become a very real problem. Motorola has several white papers that warn System Engineers of this issue. In the case of VHF systems - site noise - not the lower noise figure of the preamp - is often the limiting factor in determining the system's effective receiver sensitivity. Whereas an 800 MHz multicoupler may have a net gain of 8 to 10 dB from antenna port to receiver ports, your Sinclair unit is specified as having a net gain of only 1 dB. It is not clear from your system description if you replaced the Sinclair amp with the Anglelinear amp - or - if both are in line. Assuming the preselector and power divider loss to be on the order of 13 dB, the Sinclair amp probably has a gain of around 14 dB for a net gain of 1 dB. If you replaced that amp with the Anglelinear [which has a gain of 20 dB] plus you have installed a 2 dB atenuator - then your system net gain is 5 dB - that might either be OK or unnecessary based on the site noise floor. If you have both the Sinclair and the Anglelinear amps in line you have way too much gain. To get the receive design right - you should start by measuring the site noise floor. Directly measuring site noise is a complex subject but for starters why not just test one MTR station directly on the recevie antenna. If you have any degradation at all - that will be sufficient data to determine the site noise. The procedure is covered here: http://www.repeater-builder.com/tech-info/effectivesens.html Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2
Hi Skipp, Was hoping for the rest of your comments (after lunch), but in the mean time here are some responses to this first set. Thanks. Alex --- In Repeater-Builder@yahoogroups.com, "skipp025" <[EMAIL PROTECTED]> wrote: I'd probably Cut the repeater power output > down a bit. Since you have narly antenna gain, > I'd probably back the repeaters down to 80 > watts to possibly improve the unwanted products > from the power amplifiers (which can be measured). We tried lowering the power as far a 25W, and the interference was always still present. In view of that power was again set at 100W. Still I would agree that lowering it to 75-80W would help somewhat once additional filtering is installed, without affecting coverage too much. > Did you check the combiner for proper tuning? All > is rarely plug and play in the real world. "Trust > but verify". Did not. Assumed it was Ok, and was not sure that something else besides the pass cavities would need to be retuned (isolators?), so left it alone. Guess only the cavities need to be checked for maximum power transfer? If so will do that as part of the to-do list when we return to the site. One thing I did notice on the combiner is that one of the dummy loads on the CH1/control channel isolator (the one closest to the input) was getting quite hot to the touch. The other load on the same isolator was only getting warm. Since these are basically terminated on N-connectors I hooked up a wattmeter, but it was only showing 3W (as I recall the load is rated at 35W). Left it as is for a while and it turned out the heat was actually coming from the isolator, not from the load. Is this normal? This was happening with just CH1 transmitting (continuously). > > > (Cavity/Dual Isolator type), and a Sinclair > > RM201-112S1B RX Multicoupler fitted with a BP > > Preselector (with 1MHz pass-band, and factory > > tuned to 165.625), a "Hi Level" Bipolar preamp > > (Angle Linear brand / anglelinear.com), > > Crap, I just took a look at it. > Not enough protection... by a long shot. You need > to boot the 1 MHz band pass filter and get a real > serious vhf preselection network. Was considering changing the Preselector to a pass-reject type, and have it tuned for maximum rejection to where the TX carriers are. But I am still trying to locate a drop-in replacement of this kind, if available at all in that "compact surface mount" type. Or will I need to get one with bigger cavities? Suggestions? > > As mentioned before, you should also add some > serious receiver protection in the transmit > combiner side/path. You mean of course the notch filters. Can you suggest a specific model/brand? One you would use in your own system under the same circumstances. > Using 6 ports..? Every other coax jack should be used > to balance the internal dividers better and "mo > isolation". So I would use ports 1-3-5-7-9-11 ? Or 2-4-6-8-10-12? > > > Between the preamp output and the power divider there > > is a 2dB pad fitted. > Not good, the horse is already out of the barn... Isn't this pad used to keep the overall gain of the Preselector at zero positive gain? It was factory installed. Of course, if I have to change the Preselector, obviously this would very likely also have to be changed. > If the site is on a hill, you might do better with a bit more > vertical seperation trade. Lower the tx antenna if possible. > Increasing the vertical seperation from 45' to say... 65' will > help a lot. Nope, perfectly flat terrain all around. I've gotten the more antenna separation suggestions from others, only problem is that the tower is only 90ft, and antennas are about 40ft each in length. so not much room for separation. As it is they are already very close to each other. One thing we tried (and was also recently suggested) is to split up each DB228 into separate DB224's. We used the upper portion of the top most antenna, and the lower portion of the other. That increased the separation between the two active antennas to about 40Ft. Still the interference was present, did no seem to help much, so we hooked all up again as it was. Parallel as in right next to each other? A big no-no even > for 7/8 Hardline. The two lines had better be min 6 inches > away from each other in the the inbound tray. Yes, separating these two will also be on my to-do list. > > Combiner to repeater TX port jumpers are made of Belden 9913, > From Telewave..? or you made them up? You need to boot the > 9913 and use RG-214 min or 1/2 inch superflex hardline typical. We made them. Will use RG214, as 1/2 (even superflex) will be a bit of a pain to fit. >Crap... boot the RG-58 right away. There is no real 100% > shielded rg-58 that I've ever measured. We are now using RG142 jumpers on the RX jumpers. There is not much spacing between the output ports of the multicoupler, so fitting RG214 in there would be a bit tricky. > Not good enough... did you use any main signal notch cav
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2
From Decibel's description DB-228... >A high-gain, broadband antenna for 138-174 MHz, the 8-dipole DB228 combines two DB224E offset-pattern antennas to provide a 9 dBd gain omni or a 12 dBd gain offset horizontal pattern. Both DB224E antennas are mounted with the ends together, and the phasing harness is terminated at the center. A special bracket positions the antenna at a pre-determined distance from the tower.< you wrote... >Antenna system consists of two Decibel DB228 8-dipole arrays, mountedon a 90ft self supporting tower. RX antenna is at the top, TX ismounted from about mid-tower down. Vertical separation betweenantennas is not much due to tower height limitations, and eachantenna's length, but each DB228 is mounted on a separate adjacenttower leg.< The DB-228 is about 41 feet long. Top antenna cannot be fully top mounted due to it's size so that means that about 20 ft is side mounted. That puts the bottom of the TX antenna at 70 ft. >TX is mounted from about mid-tower down.< OK I am interperating this to mean that the top of the bottom antenna is at say 50 ft, which puts the bottom at 10 ft. Total antenna seperation 20 ft. or less. Big problem. When you purchased the system, was it engineered for this spacing or did the antenna system come later? You need more isolation between the antennas. I would strongly suggest that you replace the antennas with DB-224's (20 ft long). Aim for a minimum of 60 ft of space between the bottom of the top antenna and the top of the side mount antenna. Since the description of the DB-228 indicates that it is made of 2 DB-224E's it may be possible to simply split one of the antennas apart and test that way. If you must stay with these high gain antennas then your TX combining and RX distribution systems need to be reengineered taking into account the short spacing (low isolation) between the TX and RX antennas. Ditch the RG-58 and the 9913 and use RG-214 or Superflex for jumpers. Verify the tuning of the cavities. Things change in shipment, especially in rough terrain. Milt YAHOO! GROUPS LINKS Visit your group "Repeater-Builder" on the web. To unsubscribe from this group, send an email to: [EMAIL PROTECTED] Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.10.5/67 - Release Date: 8/9/05
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2
I get to stick my neck out first again... I've cut out mucho and added some comments. > ... 6 Motorola MTR2000 100W repeaters, I'd probably Cut the repeater power output down a bit. Since you have narly antenna gain, I'd probably back the repeaters down to 80 watts to possibly improve the unwanted products from the power amplifiers (which can be measured). > Also part of the system are a factory tuned Telewave > M101-150-6TRM TX Combiner Did you check the combiner for proper tuning? All is rarely plug and play in the real world. "Trust but verify". > (Cavity/Dual Isolator type), and a Sinclair > RM201-112S1B RX Multicoupler fitted with a BP > Preselector (with 1MHz pass-band, and factory > tuned to 165.625), a "Hi Level" Bipolar preamp > (Angle Linear brand / anglelinear.com), Crap, I just took a look at it. Not enough protection... by a long shot. You need to boot the 1 MHz band pass filter and get a real serious vhf preselection network. As mentioned before, you should also add some serious receiver protection in the transmit combiner side/path. > and a 12 port power divider. Using 6 ports..? Every other coax jack should be used to balance the internal dividers better and "mo isolation". > Between the preamp output and the power divider there > is a 2dB pad fitted. Not good, the horse is already out of the barn... > Since we only use 6 output ports of the 12 available, the > remaining ones have been fitted with 50-ohm terminators on them. Should be every other port as I described above. > Antenna system consists of two Decibel DB228 8-dipole > arrays, mounted on a 90ft self supporting tower. Nice... > RX antenna is at the top, TX is > mounted from about mid-tower down. Vertical separation between > antennas is not much due to tower height limitations, and each > antenna's length, but each DB228 is mounted on a separate adjacent > tower leg. Feedlines are 7/8 hardline running on separate tower legs If the site is on a hill, you might do better with a bit more vertical seperation trade. Lower the tx antenna if possible. Increasing the vertical seperation from 45' to say... 65' will help a lot. > up until the point where they start to get horizontal to be routed > into the building next to the tower. At this point they run parallel > to each other for about 40ft. Parallel as in right next to each other? A big no-no even for 7/8 Hardline. The two lines had better be min 6 inches away from each other in the the inbound tray. > Combiner to repeater TX port jumpers are made of Belden 9913, >From Telewave..? or you made them up? You need to boot the 9913 and use RG-214 min or 1/2 inch superflex hardline typical. > and between RX Multicoupler and RX ports we were using 100% > shield RG58. Crap... boot the RG-58 right away. There is no real 100% shielded rg-58 that I've ever measured. > Since at least one person expressed concern over the usage > of said cables, we changed the RX jumpers to RG142. Most of the pro repeater sites out here also use RG-214 for the receiver side, unless they use hard line or older RG-9. > TESTS > > One of our first tests was to look at the combiner output with a > spectrum analyzer trough a "Lossy T". It looked pretty clean > with only two or three smaller peaks on the sides of the main > carrier, all between 40-50db down or more. Not good enough... did you use any main signal notch cavities with the test set up described below? You are not going to see the problem using what you describe above. Lunch takes me away (I like to eat)... more later on. cheers, skipp Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: tx combiner follow up... UPDATE 2
Hello again everyone. Sorry for the extra long post, but wanted to make sure not to leave out anything, so as to hopefully minimize the need for further follow up questions on these facts. SYSTEM DESCRIPTION Just as a refresher, this is a 6-channel VHF MPT1327 Trunking system. It consists of 6 Motorola MTR2000 100W repeaters, fitted with a circulator on the TX output stage, and optional Preselector on the back of the unit. Also part of the system are a factory tuned Telewave M101-150-6TRM TX Combiner (Cavity/Dual Isolator type), and a Sinclair RM201-112S1B RX Multicoupler fitted with a BP Preselector (with 1MHz pass-band, and factory tuned to 165.625), a "Hi Level" Bipolar preamp (Angle Linear brand / anglelinear.com), and a 12 port power divider. Between the preamp output and the power divider there is a 2dB pad fitted. Since we only use 6 output ports of the 12 available, the remaining ones have been fitted with 50-ohm terminators on them. Antenna system consists of two Decibel DB228 8-dipole arrays, mounted on a 90ft self supporting tower. RX antenna is at the top, TX is mounted from about mid-tower down. Vertical separation between antennas is not much due to tower height limitations, and each antenna's length, but each DB228 is mounted on a separate adjacent tower leg. Feedlines are 7/8 hardline running on separate tower legs up until the point where they start to get horizontal to be routed into the building next to the tower. At this point they run parallel to each other for about 40ft. Grounding kits have been installed on each cable at the top and bottom of each run at the tower. A Polyphaser VHF50HN Surge Protector is going to be fitted soon between the equipment rack and the end of the 7/8 cable runs with a 1/2 suplerflex jumper. Also another grounding kit will be installed just prior to where the two 7/8 cables enter the building. For the time being the ends of the 7/8 lines are fitted each with a double Female N-connector (in place of the Polyphaser unit, and connected to the 1/2 suplerflex jumpers. The tower being used was in service for a cellsite, but since has been abandoned for some years. Since the tower structure is in good shape, only the grounding system proved to require some attention. Measurements show that the 4 grounding points show 995, 85, 170, and 218 ohms. The grounding system is going to be completely redone on our next visit to the site. Adjacent to the tower are three satellite up/down links. Grounding system on one of them shows less than 20-ohms (with 4 rods), so it should be no problem to get our grounding into spec. The only other system fairly close by is another VHF repeater (plain-Jane GR300), but so far apparently it does not seem to be any cause of concern. It is located on a separate tower about a mile away from ours, and has about the same height. Operating frequencies of this system are 157.700 and 162.700 (but not sure which is TX). Combiner to repeater TX port jumpers are made of Belden 9913, and between RX Multicoupler and RX ports we were using 100% shield RG58. Since at least one person expressed concern over the usage of said cables, we changed the RX jumpers to RG142, and then we found a way to temporarily hook up the combiner directly into the TX ports in order to remove all 9913 jumpers. See tests bellow for more info on this. Operating channel frequency pairs start at T160.125 R165.125 (for CH1) with 200KHz increments to T161.125 R166.125 for CH6. SYMPTOMS When the system was installed, under certain circumstances we noticed an unwanted (weak) signal appearing in one or more repeater receivers. It barely opens the squelch on the affected repeaters, but it is enough to cause problems. The signal manifests itself as an indication of the Carrier LED of each affected repeater coming on, even if the particular channel is not in use. The interference was consistent with our own operations, and did not seem to depend on other external factors, as the other repeater system mentioned before. We monitored activity of this system, and it did nothing to change our interference when it was active. Basically the interfering signal shows up as described above when several of our own TX signals are present. This normally would happen when the control channel repeater (usually CH1) is on the air, and a call is placed into the system. Interference showed up most prominently when CH5 or 6 where assigned to the call as traffic channel, but would also happen with other channels. When a call is placed, this would bring up contentiously another repeater TX for the duration of the call. The interfering signal would mostly only show up whenever the PTT of the radio that initiated the call would be keyed. This happened both with the portable being keyed right in front of the equipment rack, and also from 300-400 feet away. Although sometimes we where also able to get the interference to show up when several repeaters where transmitting at the same time, and without ne
