> "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 the Telewave 6-cav. unit has look
> pretty enticing to me.
It's not enough protection. You need to use both tight window
and series notch filters on the RX side ....and follow the Tx
Combiner output with a notch filter system if you want hand held
performance. Notching the Rx frequencies in the transmit combiner
output path before they reach the antenna is a big deal. You
currently suffer from the lack of...
> Nothing at all against DCI, but only wished Ralph could offer us a
> quicker delivery time, I really can't work in those 4 weeks he's
> offering now into our schedule. In addition to that, we also have to
> consider the shipping from Canada to Miami, and then to Caracas.
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.
>
> So you do mean something like the TWNC-150x series? I see these
> are available in 5", 8" and 10" diameter. Any suggestion what
> size would be more adequate for our needs? Not sure if we would
> need to have the steepest skirts (10"), or maybe 8" would be more
> desirable? So if I got you right, this would be ONE notch cavity
> in the Tx path for EACH of the 6 Rx frequencies?, total 6 cavities
> in series in T pass configuration? (this of course would filter
> out any wide-band Tx noise on the Rx frequencies, right?
Rx side:
I just looked a the data sheets at Telewave. If the costs allow
it, I would order a tpcp-1556 band-pass unit for the receiver and
ask them to follow it with enough twnc-1505-3 or twnc-1508-3 notch
cavity networks to provide enough notch window over the entire tx
frequency range. I would expect the number to probably be 6
cavities or two series banks of twnc-150x-3 cavities. I spec 8
inch cavities min where possible, but the 5 inch might work well
enough.
Ask Telewave to set the cable lengths up to run the notch cavity
networks right after the tpcp band pass window set up as a window
filter. Window the Rx range, notch the Tx range and be sure they
set up the notch to have min attenuation (a shoulder) to the receiver
range. You'll save a lot of grey hair by having them do the
critical cable lengths for you.
Tx side:
Order a similar twnc-150x-x 6 cavity notch assembly for the
tx side, tuned to notch the rx range and place it after the
tx combiner. Ask Telewave to provide any critical length
cables required.
> > I did a Cellwave 220 Trunking System a short time back. I could
> > scan my drawing and email you a copy of what it took to get
> > 5 channels of narrow spaced trunking to play on one antenna.
> >
> > It's pretty much the same layout as your system, just split
> > the tx/rx paths to different antenans.
>
> So I'm guessing ham radio lost some of their spectrum on that
> band to commercial applications? I understood that whole band
> was for ham operators.
We lost the 220-222 range to commercial acsb narrow band
trunking, which promptly died on the vine (most all of it,
there are small systems still on the air). I've done a lot
of work with installing the ACSB stuff, but the surplus
antenna systems from dead systems works "lo mejor" on the
amateur bands.
> Here a portion of it is used to link the FM broadcasting
> studios to the transmitters. Not much ham activity going on
> there.
We use digital connections "T-1" and the 947 MHz band for
broadcast station STL Links.
> Alex
brain on fire again...
buena suerte
su amigo
skipp
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