Re: RE: Re: RE: [Repeater-Builder] Re: Duplexers

[Ron Wright]

Loss in feedline has lots more to do with the LC in the cable than I^2R.  If 
I^R were a major factor then frequency would not have much say in the equation. 
 Skin affect is a factor, but then it would also be in twin feeder which have 
sufficent less loss over coax which has a much larger LC factor.

73, ron, n9ee/r




>From: Gary Schafer <[EMAIL PROTECTED]>
>Date: 2007/08/26 Sun PM 08:47:29 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: RE: Re: RE: [Repeater-Builder] Re: Duplexers

>  
>
>Jesse is right about skin effect beinggreater at higher frequencies on the 
>same cable. But current will be less alsoas resistance increases. Current is a 
>function of resistance for a given amountof power applied.
> 
>Coax loss is mainly due to resistive lossup thru VHF. Dielectric loss also 
>starts to come into play as you get into UHFand above. The higher the 
>frequency the higher the resistance is in the cableconductor due to skin 
>effect.
> 
>Losses due to radiation are very low andalmost immeasurable in most cases.
> 
>Open wire line will radiate very little ifit is properly balanced even when 
>SWR is very high.
> 
>The reason open wire line has less lossthan coax cable is that the impedance 
>is generally higher. The higher theimpedance the lower the current for a given 
>amount of power thus the lower theI squared R loss in the line. (Note that the 
>“R” in I squared Rloss is talking about the resistive loss in the cable 
>and not the impedance ofthe cable)
> 
>A 75 ohm coax cable with the sameapproximate size as a 50 ohm cable will have 
>lower loss than the 50 ohm cablebecause of the lower current in the cable. 
>(Less I squared R loss)
> 
>In coax cable the loss is mainlydetermined by the center conductor 
>size/surface area. Current flow is veryshallow at RF frequencies so it does 
>not matter if center conductor is solid ortubing. Tubing gets more economical 
>with larger sizes.
> 
>As the center conductor size is increasedin a cable the shield must also be 
>increased in order to maintain the samecenter conductor to shield diameter 
>ratio which maintains the impedance. If thecenter conductor size was increased 
>without changing the outer conductor theimpedance of the cable would be lower.
> 
>Losses due to SWR on the line are due topart of the signal being reflected and 
>re-reflected and suffering additionalresistive losses as it makes the second 
>(and multiple) trip up and down theline. This is not to be confused with 
>mis-match loss.
> 
>Mis-match loss is not a loss attributableto cable loss but it is a loss that 
>comes about because the transmitter doesnot see a flat 50 ohms and does not 
>transfer full power because the loading haschanged due to the impedance mis- 
>match. This type of loss is what is seen dueto poor connectors. Often 
>connector mis-match loss is confused with direct lossin the connector. Direct 
>loss produces heat as does all I squared R loss.
> 
>73
>Gary K4FMX
> 
> 
>From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of 
>Jesse Lloyd
>Sent: Sunday, August 26, 2007 3:32PM
>To: Repeater-Builder@yahoogroups.com
>Subject: Re: Re: RE:[Repeater-Builder] Re: Duplexers
> 
>Well skin effect varieswith frequency, there for the R is higher with 
>frequency.  I is constant,but R is not, so your power lost will vary with 
>frequency because of I^2R andskin effect.  This is why larger diameter solid 
>hardline has less lossthan smaller. 
>
>
>
>On 8/26/07, RonWright <[EMAIL PROTECTED]>wrote:
>Jesse,
>
>You are correct and this is why some large coax have hollow tubing for 
>theinter conductor. Due to skin effect the current density on the outer part 
>ofthe conductor is higher.
>
>But if a coax has 10 watts with a said current at one freq and the same 
>currentat a higher freq the losses will be different. This was my point.
>
>73, ron, n9ee/r
>
>>From: Jesse Lloyd <[EMAIL PROTECTED]>
>>Date: 2007/08/26 Sun PM 02:34:41 CDT
>>To: Repeater-Builder@yahoogroups.com
>>Subject: Re: RE: [Repeater-Builder] Re: Duplexers
>
>
>> 
>>I^2R losses do change with frequency because of the skineffect.
>>
>>
>>
>>On 8/26/07, Ron Wright <[EMAIL PROTECTED]>wrote: 
>>Jeff,
>>
>>The low shield coverage is one reason I do not buy cableswith pre-installed 
>>connectors unless I know the cable...not just because itsays RG8 or whatever.
>>
>>I used a piece of 50 ft RS RG8 w/pre-installed connectors fora few years and 
>>finally cut it for other purposes and was so disappointed I hadpurchased such 
>>a cable with so little shield. 
>>
>>Guess works for CB and Ham HF bands, but really not good forVHF/UHF. The same 
>>can be said for many PL259 connectors and adapters.
>>
>>73, ron, n9ee/r
>>
>>>From: Jeff DePolo <[EMAIL PROTECTED]>
>>>Date: 2007/08/26 Sun PM 12:59:45 CDT
>>>To: Repeater-Builder@yahoogroups.com
>>>Subject: RE: [Repeater-Builder] Re: Duplexers
>>
>>>
>>>Coax leakage is different than currents flowing on theshield though...
>>>
>>

Re: Re: Re: RE: [Repeater-Builder] Re: Duplexers

[Ron Wright]

Jesse,

Then why do twin feeders have much less loss than coax???  Skin affect is even 
more of a factor there due to the differences in the area of the outer shield 
in coax vs the twin feeders wire.

Maybe it is because of the larger C coupling in the coax due to the larger 
surface area of the shield.  Coax has a lower R even with skin effect than twin 
line feeders.

Skin affect is a factor, but a small one compared to the LC factor.

73, ron, n9ee/r




>From: Jesse Lloyd <[EMAIL PROTECTED]>
>Date: 2007/08/26 Sun PM 03:32:00 CDT
>To: Repeater-Builder@yahoogroups.com
>Subject: Re: Re: RE: [Repeater-Builder] Re: Duplexers

>  
>Well skin effect varies with frequency, there for the R is higher with 
>frequency.  I is constant, but R is not, so your power lost will vary with 
>frequency because of I^2R and skin effect.  This is why larger diameter solid 
>hardline has less loss than smaller.
>
>
>
>On 8/26/07, Ron Wright <[EMAIL PROTECTED]> wrote:  
>Jesse,
>
>You are correct and this is why some large coax have hollow tubing for the 
>inter conductor.  Due to skin effect the current density on the outer part of 
>the conductor is higher.
>
>But if a coax has 10 watts with a said current at one freq and the same 
>current at a higher freq the losses will be different.  This was my point.
>
>73, ron, n9ee/r
>
>>From: Jesse Lloyd <[EMAIL PROTECTED]>
>>Date: 2007/08/26 Sun PM 02:34:41 CDT
>>To: Repeater-Builder@yahoogroups.com
>>Subject: Re: RE: [Repeater-Builder] Re: Duplexers
>
>>  
>>I^2R losses do change with frequency because of the skin effect.
>>
>>
>>
>>On 8/26/07, Ron Wright <[EMAIL PROTECTED]> wrote:  
>>Jeff,
>>
>>The low shield coverage is one reason I do not buy cables with pre-installed 
>>connectors unless I know the cable...not just because it says RG8 or whatever.
>>
>>I used a piece of 50 ft RS RG8 w/pre-installed connectors for a few years and 
>>finally cut it for other purposes and was so disappointed I had purchased 
>>such a cable with so little shield.  
>>
>>Guess works for CB and Ham HF bands, but really not good for VHF/UHF.  The 
>>same can be said for many PL259 connectors and adapters.
>>
>>73, ron, n9ee/r
>>
>>>From: Jeff DePolo <[EMAIL PROTECTED]>
>>>Date: 2007/08/26 Sun PM 12:59:45 CDT
>>>To: Repeater-Builder@yahoogroups.com
>>>Subject: RE: [Repeater-Builder] Re: Duplexers
>>
>>>
>>>Coax leakage is different than currents flowing on the shield though...
>>>
>>>I remember having some RG8 from Radio Shack with braid openings that you
>>>could probably fit a pencil through.
>>> 
 Some of the cheaper coax brands have less than about 70% shielding 
 making them pretty leaky to rf.  It works just killer for adding a 
 little extra signal horse-power to a carrier current broadcast 
 station. Radiax without trying... 
>>>
>>>You could run it up the tower and have a really long antenna.  Lots of
>>>capture area ;-)
>>>
>>>
>>
>>Ron Wright, N9EE
>>727-376-6575
>>MICRO COMPUTER CONCEPTS
>>Owner 146.64 repeater Tampa Bay, FL
>>No tone, all are welcome.
>>
>>
>>
>
>Ron Wright, N9EE
>727-376-6575
>MICRO COMPUTER CONCEPTS
>Owner 146.64 repeater Tampa Bay, FL
>No tone, all are welcome.
>
>
>
>


Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.

RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers

[Jeff DePolo]

> Jesse,
> 
> Then why do twin feeders have much less loss than coax???  
> Skin affect is even more of a factor there due to the 
> differences in the area of the outer shield in coax vs the 
> twin feeders wire.

The current in a 50 ohm cable is higher as compared to a 300 ohm cable for a
given power (by a factor of the sqrt(300/50), or about 2.5) .  Power lost
due to I2R losses vary in proportion to the square of the current
(obviously), so for a given effective resistance in the conductors, a 50 ohm
cable would have 6 times greater I2R losses than a 300 ohm cable.  

But like Ron said, the conductor sizes are typically smaller in a 300 ohm
twin lead cable (as compared to, say, 7/8" Heliax), so at some point you
start getting into comparing apples and oranges...
 
> Maybe it is because of the larger C coupling in the coax due 
> to the larger surface area of the shield.  Coax has a lower R 
> even with skin effect than twin line feeders.

Again, it depends on the size of the conductors.  It's not a valid statement
that "all 300 ohm balanced lines have lower loss than 50 ohm coax".  But if
you want to compare the two cables at approximately the same size (say, the
diameter of the coax is equal to the width of the twin-lead), then the
balanced line is probably going to be the winner in the loss department at
VHF.

> Skin affect is a factor, but a small one compared to the LC factor.

Please define "the LC factor".

--- Jeff

RE: RE: Re: RE: [Repeater-Builder] Re: Duplexers

[Jeff DePolo]

Gary's got it all right, though I take minor exception with one issue:

> As the center conductor size is increasedin a cable the 
> shield must also be increased in order to maintain the 
> samecenter conductor to shield diameter ratio which maintains 
> the impedance. If thecenter conductor size was increased 
> without changing the outer conductor theimpedance of the 
> cable would be lower.

The Z is determined by the ratio of the OD of the inner and ID of the outer
AND the dielectric constant of the material between them.  You can
increase/decrease the size of one without changing the other as long as the
dielectric constant changes to compensate to keep the Z the same.  To wit:
LMR-400 vs RG-8 solid poly.

Ron - the higher in frequency you go, the less "skin depth" there is, ergo
the more resistance there is.  I2R losses almost always dominate at UHF and
below for the kinds of coax we usually work with.

Think about it this way.  If at 6m the skin effect causes your center
conductor to have the same effective cross-sectional area (due to the skin
effect) as, say, 12 gauge wire, at 440 the same coax will have an effective
cross-sectional area of something smaller, like 18 gauge wire.

--- Jeff


> -Original Message-
> From: Repeater-Builder@yahoogroups.com 
> [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright
> Sent: Monday, August 27, 2007 7:30 AM
> To: Repeater-Builder@yahoogroups.com
> Subject: Re: RE: Re: RE: [Repeater-Builder] Re: Duplexers
> 
> Loss in feedline has lots more to do with the LC in the cable 
> than I^2R.  If I^R were a major factor then frequency would 
> not have much say in the equation.  Skin affect is a factor, 
> but then it would also be in twin feeder which have sufficent 
> less loss over coax which has a much larger LC factor.
> 
> 73, ron, n9ee/r
> 
> 
> 
> 
> >From: Gary Schafer <[EMAIL PROTECTED]>
> >Date: 2007/08/26 Sun PM 08:47:29 CDT
> >To: Repeater-Builder@yahoogroups.com
> >Subject: RE: Re: RE: [Repeater-Builder] Re: Duplexers
> 
> >  
> >
> >Jesse is right about skin effect beinggreater at higher 
> frequencies on the same cable. But current will be less 
> alsoas resistance increases. Current is a function of 
> resistance for a given amountof power applied.
> > 
> >Coax loss is mainly due to resistive lossup thru VHF. 
> Dielectric loss also starts to come into play as you get into 
> UHFand above. The higher the frequency the higher the 
> resistance is in the cableconductor due to skin effect.
> > 
> >Losses due to radiation are very low andalmost immeasurable 
> in most cases.
> > 
> >Open wire line will radiate very little ifit is properly 
> balanced even when SWR is very high.
> > 
> >The reason open wire line has less lossthan coax cable is 
> that the impedance is generally higher. The higher 
> theimpedance the lower the current for a given amount of 
> power thus the lower theI squared R loss in the line. (Note 
> that the â??Râ? in I squared Rloss is talking about the 
> resistive loss in the cable and not the impedance ofthe cable)
> > 
> >A 75 ohm coax cable with the sameapproximate size as a 50 
> ohm cable will have lower loss than the 50 ohm cablebecause 
> of the lower current in the cable. (Less I squared R loss)
> > 
> >In coax cable the loss is mainlydetermined by the center 
> conductor size/surface area. Current flow is veryshallow at 
> RF frequencies so it does not matter if center conductor is 
> solid ortubing. Tubing gets more economical with larger sizes.
> > 
> >As the center conductor size is increasedin a cable the 
> shield must also be increased in order to maintain the 
> samecenter conductor to shield diameter ratio which maintains 
> the impedance. If thecenter conductor size was increased 
> without changing the outer conductor theimpedance of the 
> cable would be lower.
> > 
> >Losses due to SWR on the line are due topart of the signal 
> being reflected and re-reflected and suffering 
> additionalresistive losses as it makes the second (and 
> multiple) trip up and down theline. This is not to be 
> confused with mis-match loss.
> > 
> >Mis-match loss is not a loss attributableto cable loss but 
> it is a loss that comes about because the transmitter doesnot 
> see a flat 50 ohms and does not transfer full power because 
> the loading haschanged due to the impedance mis- match. This 
> type of loss is what is seen dueto poor connectors. Often 
> connector mis-match loss is confused with direct lossin the 
> connector. Direct loss produces heat as does all I squared R loss.
> > 
> >73
> >Gary K4FMX
> > 
> > 
> >From: Repeater-Builder@yahoogroups.com 
> [mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd
> >Sent: Sunday, August 26, 2007 3:32PM
> >To: Repeater-Builder@yahoogroups.com
> >Subject: Re: Re: RE:[Repeater-Builder] Re: Duplexers
> > 
> >Well skin effect varieswith frequency, there for the R is 
> higher with frequency.  I is constant,but

Re: Re: Re: RE: [Repeater-Builder] Re: Duplexers

[Ralph Mowery]

--- Ron Wright <[EMAIL PROTECTED]> wrote:

> Jesse,
> 
> Then why do twin feeders have much less loss than
> coax???  Skin affect is even more of a factor there
> due to the differences in the area of the outer
> shield in coax vs the twin feeders wire.
> 
> Maybe it is because of the larger C coupling in the
> coax due to the larger surface area of the shield. 
> Coax has a lower R even with skin effect than twin
> line feeders.
> 
> Skin affect is a factor, but a small one compared to
> the LC factor.
> 
> 73, ron, n9ee/r
> 

It is not open wire or coax that determins the power
loss.  It is the impedance of the line and the size of
the conductors for frequencies up to 1000 Mhz or so.

To transfer 1000 watts of power , the voltage will be
higher and the current lower in most prectical open
wire lines.  That is because the impedance will be
around 300 to 600 ohms.   Coax is usually 50 or 70
ohms.  To get 1000 watts of power through that
impedance line it requires less voltage and more
current.  

This is the principal of regular 60 hz power line
transmission.  Up the voltage to a few hundred
thousand volts and the current will go down.  This
lowers the losses.

I don't care to take time to do the calculations, but
if you take some small guage wire (say # 20)  and
space it close to make about 200 ohms line and figuer
the loss, it may be higher than some 1 inch or even
1/2 inch hardline.  

At frequencies below around 1000 Mhz the major loss is
the IsqR loss in all lines.  Radiation is a very small
part.  In coax there is a point in which the current
on the shield is not flowing but jumping from point to
point where the shield wires cross. This causes some
resistance.  That is partly why the foil shielded coax
and hardline is lower in loss than regular coax. 


   

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Re: [Repeater-Builder] Need help ID ing transistor

[Jeff Condit]

I believe you ar looking at the equivalent of a 2NA transistor.  It is an 
NPN generally good for about 40V and 600mA.  The 2N prefix was for the mil-spec 
part from which commercial equivalents were derived.  The NT prefix is some 
vendor-specific prefix.  If you search for NT you'll find a lot of stuff on 
Google, but it will be hard to sort through.  Insteaed, go to digikey.com and 
search for .  Look under discrete devices.  You'll find a lot of them.  You 
need to find a case that will fit physically.  It looks like a TO-92 so select 
that package.  You'll find about 15 of them.  Pick one that is in stock.  Looks 
like there are 6 of them.  Howabout the PNBU from Fairchild Semiconductor?  
It is 11 cents each.  If you click on the part number, and then the part number 
again under technical/Catalog Information, and then datasheets, you'll get full 
info on it.  Anyway, this is my guess.  I don't have a schematic so I don't 
know for sure, but a TO-92 has only 3 leads so its almost certainly got to be a 
transistor or FET, and the  is very very common.  You'll notice that 
different manufacturers play with the prefix to identify their product line, 
and suffixes to identify variants.  This one also cones up under the NT 
search.

Hope this helps,

Jeff Condit



  - Original Message - 
  From: John Reid 
  To: Repeater-Builder@yahoogroups.com 
  Sent: Friday, August 24, 2007 4:34 PM
  Subject: [Repeater-Builder] Need help ID ing transistor


  Forgive me, I am still relatively new at this.
  I recently bought a controller for a good price, but now I need to
  figure it out. It arrived with a broken component, I believe it is a
  transistor but the numbers do not bring back anything with Google,
  could someone help me as far as what I need to buy to replace it it is
  similar to many numbers but no identical match. It is marked as such
  NT
  
  A46C

  a picture is here 
  http://tinyurl.com/28z6tn

  Thanks in advance, and I hope you dont mind, but as I am learning I
  might ask a few questions every now and then.



   


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  Checked by AVG. 
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2:59 PM

[Repeater-Builder] subaudibe tones..

[larry allen]

Does anyone know when subaudabe tones were introduced into ham radio 
repeaters.. or more specifically when they became standard in ham radio 
sets?
Larry ve3fxq

[Repeater-Builder] Re: WANTED....power control board.

[Pete Theo]

--- In Repeater-Builder@yahoogroups.com, "Pete  Theo" <[EMAIL PROTECTED]> 
wrote:
>
> For the MSR 2000.Part TLD 9272 A  or the whole PA.Part for the PA TLD 
> 2532A.Price?
>
Anybody?

RE: [Repeater-Builder] UHF Maratrac: Low power in ham bands

[Jimmy Powell]

Bob M.

 

Thanks for the tip. I did the alignment. It was a little quirky but I
finally got the radio performing to my satisfaction. It does 100 watts plus,
from 440-450. I turned it down to 80 of course. Now I have to decide if I
want to "waste" a good Maratrac as a repeater transmitter. Maybe, I should
just order the crystal for one of the Mitreks I have laying around.

 

Thanks

Jimmy

 

  _  

From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Bob M.
Sent: Saturday, August 25, 2007 8:26 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] UHF Maratrac: Low power in ham bands

 

I think the Maratrac is based on the MaxTrac radio. As
such, you'd probably have to go through the Board
Replacement -> PA Alignment procedure which sets the
output power at 16 discrete frequencies.

On Radius radios (cousins of MaxTracs), the freqs go
from 440-470, but on MaxTracs they usually go from
449-470. Some radios can be aligned to cover 440-470.
Not all radios will work below 445 MHz without some
other retuning, so even if the PA output is properly
aligned, there may be other issues.

You need the appropriate radio service software and
paraphernalia that goes with it, plus a dummy load and
a power indicating device (wattmeter or service
monitor).

Bob M.
==
--- jimmylpowell <[EMAIL PROTECTED]  com>
wrote:

> I have a Maratrac that will only make about 20 watts
> at 446.500 and
> almost nothing a little below that. At 448.00 and
> above it makes full
> power. I have another Maratrac that makes full power
> down to 440.000.
> I did not check it any further. The radios look a
> little different
> inside. The one that has low power is HUE 2189B the
> good one is
> HUE2089B. What changes were made to the design that
> may be causing my
> problem? I want to put one of the radios in my
> service van and the
> other was going to be used as my repeater
> transmitter backup. I need
> it to transmit in the 443.000 range.
> 
> Jimmy
> KS4KX

__
Sick sense of humor? Visit Yahoo! TV's 
Comedy with an Edge to see what's on, when. 
http://tv.yahoo.  com/collections/222

 

Re: [Repeater-Builder] duplexer design

[sms mms]

I require the value of insertion loss on both frequencies.
  I have to design band reject type duplexer,please suggest the design.
  I will be grateful.
  vikash

Ron Wright <[EMAIL PROTECTED]> wrote:
  Sounds as if you are designing a duplexer with coils and caps. It is 
often this approach will not have a high enough Q to have a notch at one freq 
and at the same time pass freq with low enough insertion loss.

Normally duplexers use cavities which are made from coax made from heavy metal 
tubes, inter and outer conductors. Not your typical coax, but follow the same 
format.

You may have the notch on both frequencies, but what is the insertion loss at 
the desired pass freq.

73, ron, n9ee/r

>From: sms mms <[EMAIL PROTECTED]>
>Date: 2007/08/24 Fri PM 12:11:46 CDT
>To: repeater 
>Subject: [Repeater-Builder] duplexer design

> 
>Dear all, I am Vikash Gupta from India. I am designing a duplexer having low 
>frequency:230 MHz, High gfreuqency: 234 MHz. I am using coil with 8 no. of 
>turns and 22 PF capacitor. I have to get Insertion loss <1.2 on both low and 
>high sides. But I have a problem in getting this. I have got Rejection of more 
>than 80 dB and Return loss of better than 20 dB on both sides. Please give me 
>suggestion what I have to do? thanks in advance. Vikash  
> 5, 50, 500, 5000 - Store N number of mails in your inbox. Click here. 

Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.



 

   
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RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers

[allan crites]

It appears that the instant discussion has overlooked that there are three 
factors in the attenuation of transmission lines. They are the conductor 
losses, the dielectric losses, and
  also the optimum ratio of b/a = 3.6 for a coaxial line, which corresponds to 
a characteristic impedance of 77 ohms for a line with air dielectric.
  Obviously a solid dielectric coaxial or balanced transmission line will have 
a higher loss than a line of foam or air dielectric.
  A very complete discussion (without any high power math) of the attenuation 
of coaxial transmission lines which includes the losses in the resistivity of 
conductors and the attenuation resulting from dielectric losses is to be found 
in the publication Microwave Transmission Design Data by Theodore Moreno 
beginning on p.63 to p.66.
  There is also a graph showing the relationship of the various characteristics 
(attenuation, maximum resonant impedance, breakdown voltage, and power carrying 
capacity) of a coaxial transmission line plotted as functions of the ratio of 
radii of outer and inner conductors.
  I would suggest the respondents pursue this publication for additional 
information and end the speculation about attenuation in coaxial transmission 
lines that does not benefit the less informed readers of this group.
   
  Allan Crites  WA9ZZU
  

Jeff DePolo <[EMAIL PROTECTED]> wrote:
  > Jesse,
> 
> Then why do twin feeders have much less loss than coax??? 
> Skin affect is even more of a factor there due to the 
> differences in the area of the outer shield in coax vs the 
> twin feeders wire.

The current in a 50 ohm cable is higher as compared to a 300 ohm cable for a
given power (by a factor of the sqrt(300/50), or about 2.5) . Power lost
due to I2R losses vary in proportion to the square of the current
(obviously), so for a given effective resistance in the conductors, a 50 ohm
cable would have 6 times greater I2R losses than a 300 ohm cable. 

But like Ron said, the conductor sizes are typically smaller in a 300 ohm
twin lead cable (as compared to, say, 7/8" Heliax), so at some point you
start getting into comparing apples and oranges...

> Maybe it is because of the larger C coupling in the coax due 
> to the larger surface area of the shield. Coax has a lower R 
> even with skin effect than twin line feeders.

Again, it depends on the size of the conductors. It's not a valid statement
that "all 300 ohm balanced lines have lower loss than 50 ohm coax". But if
you want to compare the two cables at approximately the same size (say, the
diameter of the coax is equal to the width of the twin-lead), then the
balanced line is probably going to be the winner in the loss department at
VHF.

> Skin affect is a factor, but a small one compared to the LC factor.

Please define "the LC factor".

--- Jeff



 

RE: [Repeater-Builder] Duplexers

[R. K. Brumback]

I have heard this point argued for years. “Does trimming the coax affect the
SWR?”  If the length of coax has an affect on impedance, then how could it
not affect power out? We strive to maintain 50 ohms at the tail of all
devices to match the end load. GE puts matching networks in their Mastr
II’s. I have taken a MFJ-259 and soldered a PL259 only at one end and then
started trimming the coax down and watched the impedance change
significantly with each cut. Duplexers come with precise lengths of cabling.
I have heard that trimming coax only fools the meter. Not being an engineer
with millions worth of equipment I can only make a SWAG (scientific wild ass
guess) as to whether coax length makes a difference in power out.

Randy

W4CPT

 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo
Sent: Saturday, August 25, 2007 12:30 AM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] Duplexers

 

> When you put the Bird between the TX and the duplexer, you 
> have changed the
> length of the jumper cable, which upset the tuning. 

Adding a wattmeter or any other length of cable between the transmitter and
the duplexer Tx input port has no effect on the tuning of the duplexer. It
may change the load Z the transmitter sees, which may make the transmitter
happier (or sadder) depending on the resulting Z, but in no way does it
alter the tuning of the duplexer itself. 

Adding or removing cable lengths between the transmitter and duplexer also
does not change the VSWR as seen by the transmitter (minimal cable loss
effects notwithstanding)-. 

--- Jeff

-
Jeff DePolo - HYPERLINK "mailto:jd1%40broadsci.com"[EMAIL PROTECTED]
Broadcast Sciences LLC, Valley Forge PA
v: 610.917.3000
f: 610.917.3030

 


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AM
 

[Repeater-Builder] Re: subaudibe tones..

[Mark]

I do remember that the Icom 02AT had subaudiable tone as an encode 
(TX) function over 20 years ago.  As to the repeaters, it has and 
continues to be an owner option in most areas of the US.  I don't 
there is a real date as to when it was introduced in repeaters.

Mark KS4VT

--- In Repeater-Builder@yahoogroups.com, "larry allen" <[EMAIL PROTECTED]> 
wrote:
>
> Does anyone know when subaudabe tones were introduced into ham radio 
> repeaters.. or more specifically when they became standard in ham 
radio 
> sets?
> Larry ve3fxq
>

Re: Re: Re: RE: [Repeater-Builder] Re: Duplexers

[Jesse Lloyd]

The whole problem here is the comparison between high impedance twin lead
and low impedance coax.  Is the difference of impedance really coax
attenuation?  If you kept I equal between twin lead and coax who would win?
Also impedance shouldn't change because of frequency (with the exception of
extreme situations).  Its not C which defines the impedance of a cable its
RLC and Shunt conductance.

Skin effect has attenuation which increases with the square root of the
frequency, so at higher frequencies it becomes less.  Dielectric loss is
directly proportional to frequency as you go up in frequency at some point
it becomes the major factor of coax loss.  Dielectric loss is because of the
capacitor in the cable, not the capacitance.  All capacitors have loss, this
is the dielectric loss.  It has to do with the dielectric material in the
cable, air being one of the best.

Jesse


On 8/27/07, Ralph Mowery <[EMAIL PROTECTED]> wrote:
>
>
> --- Ron Wright <[EMAIL PROTECTED] > wrote:
>
> > Jesse,
> >
> > Then why do twin feeders have much less loss than
> > coax??? Skin affect is even more of a factor there
> > due to the differences in the area of the outer
> > shield in coax vs the twin feeders wire.
> >
> > Maybe it is because of the larger C coupling in the
> > coax due to the larger surface area of the shield.
> > Coax has a lower R even with skin effect than twin
> > line feeders.
> >
> > Skin affect is a factor, but a small one compared to
> > the LC factor.
> >
> > 73, ron, n9ee/r
> >
>
> It is not open wire or coax that determins the power
> loss. It is the impedance of the line and the size of
> the conductors for frequencies up to 1000 Mhz or so.
>
> To transfer 1000 watts of power , the voltage will be
> higher and the current lower in most prectical open
> wire lines. That is because the impedance will be
> around 300 to 600 ohms. Coax is usually 50 or 70
> ohms. To get 1000 watts of power through that
> impedance line it requires less voltage and more
> current.
>
> This is the principal of regular 60 hz power line
> transmission. Up the voltage to a few hundred
> thousand volts and the current will go down. This
> lowers the losses.
>
> I don't care to take time to do the calculations, but
> if you take some small guage wire (say # 20) and
> space it close to make about 200 ohms line and figuer
> the loss, it may be higher than some 1 inch or even
> 1/2 inch hardline.
>
> At frequencies below around 1000 Mhz the major loss is
> the IsqR loss in all lines. Radiation is a very small
> part. In coax there is a point in which the current
> on the shield is not flowing but jumping from point to
> point where the shield wires cross. This causes some
> resistance. That is partly why the foil shielded coax
> and hardline is lower in loss than regular coax.
>
> __
> Be a better Heartthrob. Get better relationship answers from someone who
> knows. Yahoo! Answers - Check it out.
> http://answers.yahoo.com/dir/?link=list&sid=396545433
>  
>

Re: [Repeater-Builder] Duplexers

[Jesse Lloyd]

The length of coax doesn't effect impedance.  Trimming the coax effects what
is read on the VSWR meter because what is actually happening is that there
is an interference pattern created when you have a mismatch on the end of
feedline.  This pattern is sinusoidal and changes in voltage and current
along the line, in 1/2 wave periods.  You will find max voltage peaks and
min voltage peaks.  Also current will go up and down too.  When you are
using a VSWR meter you are measuring voltage, if you move the meter to a
different spot on the cable, the voltage is different, therefor it gives you
a different reading.

Now if you put a voltage null at your transmitter, what would happen?
Normally with high SWR your transmitter will get hot because its dissipating
the reflected power into its heatsink.  If you put it at a voltage null, I
would suspect that the SWR would not get dissipated by the transmitter as
much as if you put it at a voltage peak.  The standing waves are still
there, there is still a mismatch, you will get the same power out, but its
just not going to hurt your transmitter as much because of the heat.

The only time coax length makes a difference to power out is if your using
it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
ohm cable put it on the end of 50 ohm cable you will get a match with a
112.5 ohm load.

You make an interesting point though, why does the cabling of duplexer's
need to be a certain length.  I would suspect that its because they are
looped and make an inductor. This then is part of the LC filtering, and
changing the length effects L.  But I could be wrong on that.

Jesse

On 8/27/07, R. K. Brumback <[EMAIL PROTECTED]> wrote:
>
>I have heard this point argued for years. "Does trimming the coax
> affect the SWR?"  If the length of coax has an affect on impedance, then how
> could it not affect power out? We strive to maintain 50 ohms at the tail of
> all devices to match the end load. GE puts matching networks in their Mastr
> II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
> started trimming the coax down and watched the impedance change
> significantly with each cut. Duplexers come with precise lengths of cabling.
>  I have heard that trimming coax only fools the meter. Not being an engineer
> with millions worth of equipment I can only make a SWAG (scientific wild ass
> guess) as to whether coax length makes a difference in power out.
>
> Randy
>
> W4CPT
>
>
>
> -Original Message-
> *From:* Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED]
> ups.com] *On Behalf Of *Jeff DePolo
> *Sent:* Saturday, August 25, 2007 12:30 AM
> *To:* Repeater-Builder@yahoogroups.com
> *Subject:* RE: [Repeater-Builder] Duplexers
>
>
>
> > When you put the Bird between the TX and the duplexer, you
> > have changed the
> > length of the jumper cable, which upset the tuning.
>
> Adding a wattmeter or any other length of cable between the transmitter
> and
> the duplexer Tx input port has no effect on the tuning of the duplexer. It
> may change the load Z the transmitter sees, which may make the transmitter
> happier (or sadder) depending on the resulting Z, but in no way does it
> alter the tuning of the duplexer itself.
>
> Adding or removing cable lengths between the transmitter and duplexer also
> does not change the VSWR as seen by the transmitter (minimal cable loss
> effects notwithstanding).
>
> --- Jeff
>
> -
> Jeff DePolo - [EMAIL PROTECTED] 
> Broadcast Sciences LLC, Valley Forge PA
> v: 610.917.3000
> f: 610.917.3030
>
>
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.484 / Virus Database: 269.12.6 - Release Date: 8/24/2007
> 12:00 AM
>
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.484 / Virus Database: 269.12.6 - Release Date: 8/24/2007
> 12:00 AM
>
>  
>

RE: [Repeater-Builder] Duplexers

[n9wys]

One can also use 1/4- and 1/2- λ stubs of coaxial cable of the same
impedance as matching networks in conjunction with a "Tee" connector.
"Shorting" or "Opening" the end of the matching stub also makes a
difference, based upon the length being employed.

I believe that VSWR is *one* reason that cabling on a duplexer must be a
function of length, based upon a fraction of the characteristic frequency.
But not being a "duplexer person" I'm not all that familiar with the precise
engineering behind their interconnecting cabling.

Mark - N9WYS


From: Repeater-Builder@yahoogroups.com On Behalf Of Jesse Lloyd

--- snip ---

The only time coax length makes a difference to power out is if your using
it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
ohm cable put it on the end of 50 ohm cable you will get a match with a
112.5 ohm load.

You make an interesting point though, why does the cabling of duplexer's
need to be a certain length.  I would suspect that its because they are
looped and make an inductor. This then is part of the LC filtering, and
changing the length effects L.  But I could be wrong on that. 

Jesse

On 8/27/07, R. K. Brumback wrote:
I have heard this point argued for years. "Does trimming the coax affect the
SWR?"  If the length of coax has an affect on impedance, then how could it
not affect power out? We strive to maintain 50 ohms at the tail of all
devices to match the end load. GE puts matching networks in their Mastr
II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
started trimming the coax down and watched the impedance change
significantly with each cut. Duplexers come with precise lengths of cabling.
 I have heard that trimming coax only fools the meter. Not being an engineer
with millions worth of equipment I can only make a SWAG (scientific wild ass
guess) as to whether coax length makes a difference in power out.
Randy
W4CPT
 





 
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[Repeater-Builder] Re: subaudibe tones..

[skipp025]

Many of the early repeaters were placed on the air by people working 
in two-way radio shops using surplus commercial radio equipment. One 
of our local long time legacy repeaters started life as a surplus 
Motorola Research Line tube unit. Sub Tone or CTCSS operation was 
added later with a bolt on chassis using the famous long copper tone 
reeds. I would guess that era to be sometime between 1965 and 1975 
when 2m repeaters first caught on (became popular) with the general 
ham public.  

Ham Radio Ops started adding ctcss when repeater problems required 
restricted operation. 

There are/were a number of after market ctcss generators... just
thinking back about some of those boat anchor add-on tone boxes 
that were bigger than some of the current radios you now operate. 

The 555 timer chip solved a lot of the ctcss generator cost problems 
and we cranked out these "hummers" en masse. Three or four wires 
in the right place and we were off and running. A copy of that 
original 1970's circuit is on the sonic page. 

http://www.radiowrench.com/sonic/so02148.html 

After a decade or more of do-it yourself ctcss encoder installs, 
the Amateur Radio Market started placing single tone ctcss encoders 
into radios in the late 70's early mid 80's. 

Early Heathkit & KDK units come to mind as radios sold with one or 
more available ctcss tone frequencies available. 

Mid 1980's saw the migration toward multi or front panel selectable 
ctcss operation with less quirky designs and controls. Some time 
along the mid 80's hams also started using DCS (digital ctcss) in 
specialized aps. 

Many of the rural parts of the US don't use constant CTCSS repeater 
control. CTCSS operation is pretty much a must have in most Metro 
Areas. 

So... now ya know. 

cheers, 
s. 



> "larry allen" <[EMAIL PROTECTED]> wrote:
> Does anyone know when subaudabe tones were introduced into ham radio 
> repeaters.. or more specifically when they became standard in ham 
> radio sets?
> Larry ve3fxq

Re: [Repeater-Builder] Re: subaudibe tones..

[JOHN MACKEY]

The Icom 02AT was either the first, or nearly the first, to offer built in
programmable CTCSS.

-- Original Message --
Received: Mon, 27 Aug 2007 11:16:29 AM CDT
From: "Mark" <[EMAIL PROTECTED]>
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Re: subaudibe tones..

> I do remember that the Icom 02AT had subaudiable tone as an encode 
> (TX) function over 20 years ago.  As to the repeaters, it has and 
> continues to be an owner option in most areas of the US.  I don't 
> there is a real date as to when it was introduced in repeaters.
> 
> Mark KS4VT
> 
> --- In Repeater-Builder@yahoogroups.com, "larry allen" <[EMAIL PROTECTED]> 
> wrote:
> >
> > Does anyone know when subaudabe tones were introduced into ham radio 
> > repeaters.. or more specifically when they became standard in ham 
> radio 
> > sets?
> > Larry ve3fxq
> >
> 
> 
> 

RE: [Repeater-Builder] Duplexers

[R. K. Brumback]

Quote from Jesse: “When you are using a VSWR meter you are measuring
voltage, if you move the meter to a different spot on the cable, the voltage
is different, therefore it gives you a different reading.”

 

This now makes more sense to me as I once saw a feed line demonstration with
voltage and current sleds showing the difference at different points along
the line. At some places the voltage was null (as with any sine wave). I
don’t see how this could happen at the antenna port of a transmitter unless
it was microwave as the cabling from the tuner to the output connector is
not near ½ wave.  Also to Alan, I appreciate your sympathy for us “little
people” but I do find this very interesting. And as you can see, the experts
sometimes need a tune up.

Randy

W4CPT

 

-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Jesse Lloyd
Sent: Monday, August 27, 2007 12:48 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] Duplexers

 

The length of coax doesn't effect impedance.  Trimming the coax effects what
is read on the VSWR meter because what is actually happening is that there
is an interference pattern created when you have a mismatch on the end of
feedline.  This pattern is sinusoidal and changes in voltage and current
along the line, in 1/2 wave periods.  You will find max voltage peaks and
min voltage peaks.  Also current will go up and down too.  When you are
using a VSWR meter you are measuring voltage, if you move the meter to a
different spot on the cable, the voltage is different, therefor it gives you
a different reading. 

Now if you put a voltage null at your transmitter, what would happen?
Normally with high SWR your transmitter will get hot because its dissipating
the reflected power into its heatsink.  If you put it at a voltage null, I
would suspect that the SWR would not get dissipated by the transmitter as
much as if you put it at a voltage peak.  The standing waves are still
there, there is still a mismatch, you will get the same power out, but its
just not going to hurt your transmitter as much because of the heat. 

The only time coax length makes a difference to power out is if your using
it in a matching stub, or a matching section ie. if you take 1/4 wave of 75
ohm cable put it on the end of 50 ohm cable you will get a match with a
112.5 ohm load.

You make an interesting point though, why does the cabling of duplexer's
need to be a certain length.  I would suspect that its because they are
looped and make an inductor. This then is part of the LC filtering, and
changing the length effects L.  But I could be wrong on that. 

Jesse

On 8/27/07, R. K. Brumback mailto:[EMAIL PROTECTED]"[EMAIL PROTECTED]> wrote:

I have heard this point argued for years. "Does trimming the coax affect the
SWR?"  If the length of coax has an affect on impedance, then how could it
not affect power out? We strive to maintain 50 ohms at the tail of all
devices to match the end load. GE puts matching networks in their Mastr
II's. I have taken a MFJ-259 and soldered a PL259 only at one end and then
started trimming the coax down and watched the impedance change
significantly with each cut. Duplexers come with precise lengths of cabling.
I have heard that trimming coax only fools the meter. Not being an engineer
with millions worth of equipment I can only make a SWAG (scientific wild ass
guess) as to whether coax length makes a difference in power out.

Randy

W4CPT

 

-Original Message-
From: HYPERLINK
"mailto:Repeater-Builder@yahoogroups.com"[EMAIL PROTECTED]
[mailto:HYPERLINK "mailto:Repeater-"; [EMAIL PROTECTED] HYPERLINK
"http://ups.com"; \nups.com] On Behalf Of Jeff DePolo
Sent: Saturday, August 25, 2007 12:30 AM
To: HYPERLINK
"mailto:Repeater-Builder@yahoogroups.com"[EMAIL PROTECTED]
Subject: RE: [Repeater-Builder] Duplexers

 

> When you put the Bird between the TX and the duplexer, you 
> have changed the
> length of the jumper cable, which upset the tuning. 

Adding a wattmeter or any other length of cable between the transmitter and
the duplexer Tx input port has no effect on the tuning of the duplexer. It
may change the load Z the transmitter sees, which may make the transmitter
happier (or sadder) depending on the resulting Z, but in no way does it
alter the tuning of the duplexer itself. 

Adding or removing cable lengths between the transmitter and duplexer also
does not change the VSWR as seen by the transmitter (minimal cable loss
effects notwithstanding)-. 

--- Jeff

-
Jeff DePolo - HYPERLINK "mailto:jd1%40broadsci.com"; [EMAIL PROTECTED]
Broadcast Sciences LLC, Valley Forge PA
v: 610.917.3000
f: 610.917.3030

 

No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.5.484 / Virus Database: 269.12.6 - Release Date: 8/24/2007 12:00
AM

 

No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.484 / Virus Database

Re: [Repeater-Builder] Re: subaudibe tones..

[Ken Arck]

At 10:27 AM 8/27/2007, you wrote:

>dded later with a bolt on chassis using the famous long copper tone
>reeds. I would guess that era to be sometime between 1965 and 1975
>when 2m repeaters first caught on (became popular) with the general
>ham public.