Topband: CAT5 for Flag Antenna Feedline ?

[JC N4IS]

Bob

Here the missing part of my original post to motivate you to try a single
twisted pair.

See bellow Ilian's comments about the performance of the RX antenna. Illian
was not detuning his TX antenna.

Regards
JC
N4IS

hi Jose
 
[12:02:50 PM] Ilian: My log is already uploaded on LoTW and ClubLog
 
[12:03:23 PM] Ilian: 1394 QSO on 160m
 
[12:04:15 PM] Ilian: more than 1200 QSOs after RX antenna installing
 
[12:05:02 PM] Ilian: about 150 QSOs without RX antenna for more than 2
months on the air
 
[12:05:57 PM] Ilian: 1200 QSOs made with RX antenna for 1 month and 10 days
 
[12:06:49 PM] Ilian: 68 DXCC worked on 160m during the all operation
 
[12:07:49 PM] Ilian: about 40 countries worked after RX antenna installing
within 1 month and 10 days
 
[12:09:49 PM] Ilian: 3865 QSOs on 80m during the all operation, about 2500
worked after RX antenna installing
 
[12:10:24 PM] Ilian: 112 DXCC worked on 80m for whole period
 
[12:11:54 PM] Ilian: about 50 new DXCC worked after RX antenna installing
for a month and 10 days
 
[12:13:36 PM] Ilian: http://t6lg.com/?page_id=221
 
[12:14:05 PM] Ilian: you can see all statistics here
 
[12:15:57 PM] Ilian: Thank you, Jose!

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Bob K6UJ
Sent: Monday, September 09, 2013 10:20 AM
To: topband List List
Subject: Re: Topband: CAT5 for Flag Antenna Feedline ?

Jim,

Your hams guide to RFI is my bible for mitigating RFI issues.  My feedline
chokes are all designed from this great article.  I probably have optimized
my feedline to the flag in regards to common mode noise but after reading
the post I was curious about CAT5.  Before possibly wasting my time
experimenting with CAT5 for feeding my flag I wanted to learn more about it.
Below is a paragraph from the Topband reflector  thread titled "high
performance receive antenna at T6LG" that sparked my interest.  They were
discussing the delta shaped flag they used which was used  before on the
FO0AAA dxpedition.  

Bob
K6UJ

The parts for the antenna was very simple, a 9"1 balun and a 910 ohms
resistor, and a 100 to 75 ohms BALUN to feed the preamp. The key component
here was the CAT 5 single twisted pair to feed the flag antenna without any
common mode noise pickup (it is necessary to strip the CAT5 and separate
each of the 4 pairs), a coax cable won't work in high noise environment,
even with a killer choke the ground does not help to stop the common node
noise. That was not the first time a twisted pair saved the day, two years
ago  I suggested Rolf PY1RO a similar antenna fed with twisted pair that
worked very well, bringing the noise to zero in a s9+20 noise environment.

On Sep 8, 2013, at 11:12 PM, Jim Brown wrote:

> On 9/8/2013 10:30 PM, Bob K6UJ wrote:
>> I got the impression from the post
>> that CAT5 is immune to common mode noise.
> 
> I've not heard that, nor can I think of a theoretical basis for saying so.
CAT5 is very good twisted pair, with a high twist ratio, Zo = 100 ohms, and
its loss is low enough to make it work fine on 160M.  The primary advantage
of twisted pair is that it rejects DIFFERENTIAL mode noise. Rejection is
greatest when both ends of the line are balanced.
> 
> One possible source of your confusion may be reading, but not fully
understanding, my work, and Neil Muncy's work, on SCIN, whereby certain
deficiencies in the construction of a cable shield convert common mode
current to a differential voltage on the signal pair. I have on several
occasions observed that high quality unshielded twisted pair, like CAT5/6/7,
would have much better noise rejection than that sort of cable.  Read about
it in several tech papers and tutorials on my website. No need to burden the
list with it.
> 
> 73, Jim K9YC
> 
> _________________
> Topband Reflector

_________________
Topband Reflector