Topband: CAT5 for Flag Antenna Feedline ?

[Bob K6UJ]

JC,

Thanks for the info, much appreciated.  I see that I need 
to go ahead and try CAT5 and see how it compares to coax for my flag feedline.

73,
Bob
K6UJ

On Sep 9, 2013, at 5:08 PM, JC N4IS wrote:

> 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
>