Re: Topband: RG-179 Coax

[Richard (Rick) Karlquist]

On 2/14/2020 1:04 PM, Jim Brown wrote:

On 2/14/2020 11:40 AM, Fred Moeves wrote:

Can you figure out impedance of coax with a device like the Rig Expert?


Yes, if it's a model that can be calibrated, and if the calibration is 
properly done, and if it's a model that can export measurements to a 
computer. Calibration requires of Standard Short, Open, and Load parts. 
Once you've calibrated, sweep a length of the coax with the far end open 
and again with it shorted. Export the data to a computer, then import it 
into AC6LA's free ZPlots Excel spreadsheet and follow his instructions. 
For the measurements, the coax must be connected at precisely the same 
point as where the calibration was done.


Before attempting this, study parts of the manual for the equipment that 
talks about the "measurement plane."


73, Jim K9YC



This is the "hard" way to measure Zo.  Been there, done that.

The easy way is to attach a small 100 ohm (non-wire-wound) pot to one 
end of the coax and attach the other end of the coax to any old 
impedance meter.  Even an MFJ-259 will work.  Now adjust the pot until 
you see a constant impedance across all frequencies.  Don't worry about 
what the impedance meter says this impedance is.  Instead, measure the 
DC resistance of the pot.  More accurate.  Foolproof.


Rick N6RK
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Re: Topband: RG-179 Coax

[Jim Brown]

On 2/14/2020 12:59 PM, CUTTER DAVID wrote:
However, in my experience cmc causes erroneous swr readings on antenna 
analysers I have used.  I would say it's almost useless to measure swr 
until cmc is eliminated.


The proper location for the first common mode choke is at the feedpoint. 
When it is inserted, it 1) adds to the length of the line; and 2) 
isolates the feedline from the antenna so that it cannot detune the 
antenna; and 3) may shift the APPARENT resonance of the antenna by 
virtue of this isolation, AND by whatever impedance transformation along 
the feedline that occurs by the addition of the choke.


This is all predicted by the fundamentals of how transmission lines 
work. Consider any real antenna -- it's feedpoint Z will be affected by 
height, surrounding objects, etc., AND will be different at every 
frequency. VERY few antennas have a feedpoint Z that is precisely equal 
to the feedline Zo over the range of operating frequencies (i.e., the 
width of a band), so any change made to the feedline can change the 
apparent resonance.


Take the simple example of a dipole resonant on the band. It's feedpoint 
Z at resonance will vary depending on its height above ground, soil 
conductivity, and surrounding objects. Specifically, the soil acts as a 
passive element of the antenna -- the reflection from it changes the 
feedpoint Z just like any other passive element, and HOW it changes it 
depends on the strength of the reflection and the phase shift 
corresponding to 2X the antenna's height. There are plots in ON4UN's 
"Low Band DXing" that show how feedpoint Z oscillates around its nominal 
value with height for certain ground conductivity values, and modeling 
software like NEC can predict it. In general, dipoles that are 
electrically low tend to be a better match to 50 ohm feedline, while 
those that are electrically high tend closer to 75 ohm coax. My high 
dipoles (hung at about 40m high from tall trees) for 80 and 40M measure 
in the range of 85 ohms at resonance. The measurement is done with a 
vector analyzer in the shack and exported to SimSmith, where the 
electrical length of the feedline is subtracted from the measured data. 
The feedline length is obtained by a TDR.


Similarly, feedpoint Z of vertical antennas will be affected by the 
radial/counterpoise system, ground losses, and surrounding objects.


73, Jim K9YC
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Re: Topband: RG-179 Coax

[Jim Brown]

On 2/14/2020 11:40 AM, Fred Moeves wrote:

Can you figure out impedance of coax with a device like the Rig Expert?


Yes, if it's a model that can be calibrated, and if the calibration is 
properly done, and if it's a model that can export measurements to a 
computer. Calibration requires of Standard Short, Open, and Load parts. 
Once you've calibrated, sweep a length of the coax with the far end open 
and again with it shorted. Export the data to a computer, then import it 
into AC6LA's free ZPlots Excel spreadsheet and follow his instructions. 
For the measurements, the coax must be connected at precisely the same 
point as where the calibration was done.


Before attempting this, study parts of the manual for the equipment that 
talks about the "measurement plane."


73, Jim K9YC


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Re: Topband: RG-179 Coax

[Fred Moeves]

Jim,

That's what I thought.

Can you figure out impedance of coax with a device like the Rig Expert?

Also I was only sending the info to somewhat confirm it's 75 ohm cable 
because it's not marked.


I was not saying that it's a good or effective choke because the SWR was 
good.


Thank You

Fred KB4QZH


On 2/14/2020 2:02 PM, Jim Brown wrote:

On 2/14/2020 9:11 AM, Fred Moeves wrote:
I put 75 resistor and 50 ohm dummy load on each choke and scanned it 
with the Rig Expert 230 zoom and it seems fine.


Common mode chokes do not affect SWR, and measuring SWR tells nothing 
about their effectiveness. See http://k9yc.com/2018Cookbook.pdf


73, Jim K9YC

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Re: Topband: RG-179 Coax

[Jim Brown]

On 2/14/2020 9:11 AM, Fred Moeves wrote:
I put 75 resistor and 50 ohm dummy load  on each choke and scanned it 
with the Rig Expert 230 zoom and it seems fine.


Common mode chokes do not affect SWR, and measuring SWR tells nothing 
about their effectiveness. See http://k9yc.com/2018Cookbook.pdf


73, Jim K9YC

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Re: Topband: RG-179 Coax

[Fred Moeves]

Mike,

I bought some from this Link 
 
.


It seems ok to me.

No markings on it and the guy could use a lesson on how to coil wire.


I put 75 resistor and 50 ohm dummy load  on each choke and scanned it 
with the Rig Expert 230 zoom and it seems fine.


I scanned it from 100khz to 10mhz ... SWR was 1:00 to 1:35... and on a 
50 ohm dummy it was 1:12 to 1:35.


Not really sure if that tells anything but there it is.

I have nothing to measure L or C.

I did try shorting one end of the coax then scanned it with the 230 zoom 
read L and C and then calculate the impedance but didn't look right.


Bad math on my part I'm sure.

I also bought these connectors and the worked just fine...Link 



And Link 2 




I have made four on these chokes now all test the same.

I have one in service and waiting for the rain to stop to install the 
other ones.



I am replacing old chokes that work but take up to much room...I'm sure 
I will see no change when I do this.


The old chokes were made from old Commscope RG 59 with 4" cores..works 
but too big...


Also I can send you a piece if you want to see it or. better yet how 
much do you need?


I think I used 5.5 feet for each choke.

73

Fred KB4QZH


On 2/13/2020 6:31 PM, W0MU Mike Fatchett wrote:
I am looking for a good source for RG-179 coax to build some RX 
antennas.  I tried an Ebay seller and got rg58!!


W0MU
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Re: Topband: RG-179 Coax

[Ham Hicks]

The Amphenol 21-579 I mentioned earlier is very flexible.
KB4BR

-Original Message-
From: Topband [mailto:topband-bounces+ham306=bellsouth@contesting.com] On 
Behalf Of W0MU Mike Fatchett
Sent: Friday, February 14, 2020 2:40 AM
To: Andreas Junge 
Cc: 160 
Subject: Re: Topband: RG-179 Coax

I am making some receive antennas and the coax will be for the choke that goes 
through a torriod.  The cores I have would not take rg6. This is from the YCCC 
receive antenna array.

W0MU

On 2/13/2020 5:55 PM, Andreas Junge wrote:
> Mike,
>
> What’s wrong with RG6? Or the DX Engineering version of it:
>
> https://www.dxengineering.com/search/department/cable-and-connectors/p
> roduct-line/dx-engineering-f6-75-ohm-bulk-coaxial-cable?autoview=SKU
> eyword=rg6=BestKeywordMatch=Ascending
>
> $0.30/foot
>
> Plenty good for RX antenna use.
>
> 73, Andreas, N6NU
>
>> On Feb 13, 2020, at 3:31 PM, W0MU Mike Fatchett > <mailto:w...@w0mu.com>> wrote:
>>
>> I am looking for a good source for RG-179 coax to build some RX 
>> antennas.  I tried an Ebay seller and got rg58!!
>>
>> W0MU
>> _
>> Searchable Archives: http://www.contesting.com/_topband - Topband 
>> Reflector
>

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Re: Topband: RG-179 Coax

[Thomas]

Hi Jim,

I use Belden 9221 miniature 75-Ohm coax for my receive antenna chokes. It is 
very flexible making it easy to wind over the torroid core. I recently bought 
100' of 9221 on ebay for a very reasonable price. It is readily available there 
and seems to do the job.

Thomas - ac7a

> On February 14, 2020 at 4:56 AM Jim Brown  mailto:j...@audiosystemsgroup.com > wrote:
> 
> 
> On 2/13/2020 11:40 PM, W0MU Mike Fatchett wrote:
> 
> > > I am making some receive antennas and the coax will be for the 
> choke
> > that goes through a torriod.
> > 
> > > As Mike understands, RG6 doesn't work. See pages 3 of
> http://k9yc.com/2018Cookbook.pdf
> 
> 73, Jim K9YC
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> Reflector
> 
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Re: Topband: RG-179 Coax

[Jim Brown]

On 2/13/2020 11:40 PM, W0MU Mike Fatchett wrote:
I am making some receive antennas and the coax will be for the choke 
that goes through a torriod.


As Mike understands, RG6 doesn't work. See pages 3 of 
http://k9yc.com/2018Cookbook.pdf


73, Jim K9YC
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Re: Topband: RG-179 Coax

[W0MU Mike Fatchett]

I am making some receive antennas and the coax will be for the choke 
that goes through a torriod.  The cores I have would not take rg6. This 
is from the YCCC receive antenna array.


W0MU

On 2/13/2020 5:55 PM, Andreas Junge wrote:

Mike,

What’s wrong with RG6? Or the DX Engineering version of it:

https://www.dxengineering.com/search/department/cable-and-connectors/product-line/dx-engineering-f6-75-ohm-bulk-coaxial-cable?autoview=SKU=rg6=BestKeywordMatch=Ascending

$0.30/foot

Plenty good for RX antenna use.

73, Andreas, N6NU

On Feb 13, 2020, at 3:31 PM, W0MU Mike Fatchett > wrote:


I am looking for a good source for RG-179 coax to build some RX 
antennas.  I tried an Ebay seller and got rg58!!


W0MU
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Re: Topband: RG-179 Coax

[Jorge Diez - CX6VM]

you ccan try CommScope F660BEF on eBay, les than 0.10/ft

Was recommended here before

73,
Jorge
CX6VM/CW5W

El jue., 13 feb. 2020 a las 21:55, Andreas Junge ()
escribió:

> Mike,
>
> What’s wrong with RG6? Or the DX Engineering version of it:
>
>
> https://www.dxengineering.com/search/department/cable-and-connectors/product-line/dx-engineering-f6-75-ohm-bulk-coaxial-cable?autoview=SKU=rg6=BestKeywordMatch=Ascending
> <
> https://www.dxengineering.com/search/department/cable-and-connectors/product-line/dx-engineering-f6-75-ohm-bulk-coaxial-cable?autoview=SKU=rg6=BestKeywordMatch=Ascending
> >
>
> $0.30/foot
>
> Plenty good for RX antenna use.
>
> 73, Andreas, N6NU
>
> > On Feb 13, 2020, at 3:31 PM, W0MU Mike Fatchett  wrote:
> >
> > I am looking for a good source for RG-179 coax to build some RX
> antennas.  I tried an Ebay seller and got rg58!!
> >
> > W0MU
> > _
> > Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
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> Reflector
>


-- 
73,
Jorge
CX6VM/CW5W
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Re: Topband: RG-179 Coax

[Andreas Junge]

Mike,

What’s wrong with RG6? Or the DX Engineering version of it:

https://www.dxengineering.com/search/department/cable-and-connectors/product-line/dx-engineering-f6-75-ohm-bulk-coaxial-cable?autoview=SKU=rg6=BestKeywordMatch=Ascending
 


$0.30/foot 

Plenty good for RX antenna use. 

73, Andreas, N6NU

> On Feb 13, 2020, at 3:31 PM, W0MU Mike Fatchett  wrote:
> 
> I am looking for a good source for RG-179 coax to build some RX antennas.  I 
> tried an Ebay seller and got rg58!!
> 
> W0MU
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Re: Topband: RG-179 Coax

[Fred Moeves]

Mike,

I bought some from ebay and also some connectors.

I made several chokes and some RX switching parts.

I'm out now and don't have access to my PC.

The cable seemed fine.

I'll put the info on here in tomorrow.


Fred KB4QZH

On 2/13/2020 6:31 PM, W0MU Mike Fatchett wrote:
I am looking for a good source for RG-179 coax to build some RX 
antennas.  I tried an Ebay seller and got rg58!!


W0MU
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Re: Topband: RG-179 Coax

[Richard (Rick) Karlquist]

This is actually an excellent price.
The "usual suspects" like DigiKey and Pasternack
get quite a bit more.  The cheapest miniature coax
is RG174 (polyethylene) and even that is not so
cheap, at least at the vendors above.

Rick N6RK

On 2/13/2020 4:21 PM, Roy Morgan wrote:

Or
The RF connection
.56/ foot
$45.00 100 feet
Reconnection.com

(That is 75 ohm Teflon coax)

Roy Morgan
K1LKY Western Mass


On Feb 13, 2020, at 6:32 PM, W0MU Mike Fatchett  wrote:

I am looking for a good source for RG-179 coax to build some RX antennas.  I 
tried an Ebay seller and got rg58!!

W0MU
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Re: Topband: RG-179 Coax

[Roy Morgan]

Or 
The RF connection
.56/ foot
$45.00 100 feet
Reconnection.com

(That is 75 ohm Teflon coax)

Roy Morgan
K1LKY Western Mass

> On Feb 13, 2020, at 6:32 PM, W0MU Mike Fatchett  wrote:
> 
> I am looking for a good source for RG-179 coax to build some RX antennas.  I 
> tried an Ebay seller and got rg58!!
> 
> W0MU
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Re: Topband: RG-179 Coax

[Roy Morgan]

Do web search for:

The Wireman



Roy Morgan
K1LKY Western Mass

> On Feb 13, 2020, at 6:32 PM, W0MU Mike Fatchett  wrote:
> 
> I am looking for a good source for RG-179 coax to build some RX antennas.  I 
> tried an Ebay seller and got rg58!!
> 
> W0MU
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Topband: RG-179 Coax

[W0MU Mike Fatchett]

I am looking for a good source for RG-179 coax to build some RX 
antennas.  I tried an Ebay seller and got rg58!!


W0MU
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