[TenTec] Trading radios

Sun Jun 1 21:18:23 EDT 2014

Regarding coaxial cables, RF current flows on the outer skin of the center 
conductor and on the inner skin of the shield.  Thus the reason for silver 
plated center conductors and silver plated shield material.    As to coaxial 
cable radiation, this is largely dependant on the percentage of shield for 
the specific cable.  For that reason, tightly shielded application 
requirements will use double shield silver plated cables such as RG-9. 
Lines made using solid aluminum outer conductor or copper outer conductor 
are known as "hard lines" and offer theoretical 100% shielding.

<quote>
"The currents in coaxial cable flow on the outside of the center conductor 
and the inside of the outer shield."  ARRL Handbook, 2014, page 20.2.

<quote>
"Common-mode currents are conducted and induced into the outside of the 
shield of the feed line, which in turn radiates."  ARRL Handbook, 2014, page 
20.17

My earlier statement regarding using "a 1:1 common mode choke" is a 1:1 
current balun at the feed point to attain a balanced to unbalanced condition 
for a center fed dipole with a coaxial feed.  This is immediately followed 
by a common mode choke at the feed point to account for any natural 
unbalance of the installation.

With a true flat top dipole and the feed line exiting precisely at 90 
degrees from plane, there is little current induced in the coax feed. 
However, any angle departure from 90 degrees, including that of a so called 
inverted V,   is likely to have significant common mode current induced into 
the feed line.  With the proliferation of inverted V usage, largely to ease 
of installation, we see a notable increase in common mode current issues.

<quote>
" Reducing common-mode current on a feed line also reduces:
* Radiation from the feed line that can distort an antenna's radiation 
pattern
* Radiation from the feed line that can cause RFI to nearby devices
* RF current in the shack and on power line wiring
* Coupling of noise currents on the feed line to receivers and receiving 
antennas
* Coupling between different antennas via their feed lines"
ARRL Handbook, 2014, page 20-18

73
Bob, K4TAX

----- Original Message ----- 
From: "Mike Schatzberg" <cherokeehillfarm at earthlink.net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Sunday, June 01, 2014 5:13 PM
Subject: Re: [TenTec] Trading radios

> What I said was:
>
> "With good quality cable, the center conductor is not radiating.  However, 
> the shield may indeed be carrying current."
>
> I don't think you have my meaning and have taken it out of context.
>
> The percentage of braid coverage, the use of foils under the braid, double 
> braids, and aspects of the cable insulation and geometry, can be factors 
> in radiation. The common mode current can still be an issue, due to the 
> direction of the cable run and it's length with regard to frequency.
>
> If you believe that there are no differences in various types of 50 ohm 
> coax, with regard to radiation from the cable, this does not agree with my 
> experience.
>
> 73,
>
> Mike
> W2AJI
>
> Sent from my iPhone
>
>> On Jun 1, 2014, at 3:59 PM, "Rick - DJ0IP / NJ0IP" <Rick at DJ0IP.de> wrote:
>>
>> Mike is doing it CORRECTLY.
>>
>> My only comment is, the quality of the coax plays NO ROLE in this.
>> CMC flows on the outside of the coax shield so it makes no difference if 
>> you
>> are using the best or the worst coax in the world - (as far as CMC is
>> concerned; of course you should use good coax for other reasons).
>>
>> 73 - Rick, DJ0IP
>> (Nr. Frankfurt am Main)
>>
>>
>> -----Original Message-----
>> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Mike
>> Schatzberg
>> Sent: Sunday, June 01, 2014 7:39 PM
>> To: Discussion of Ten-Tec Equipment
>> Subject: Re: [TenTec] Trading radios
>>
>> In my case the RF is radiated from my Yagi and the coax shield picks up 
>> the
>> radiation between the antenna feed point and the radio.
>>
>> With good quality cable, the center conductor is not radiating.  However,
>> the shield may indeed be carrying current.
>>
>> Stations with RFI often only experience interference with their 
>> directional
>> arrays with the antenna in a certain alignment with their cable.
>>
>> I use a 1:1 current balun at my Yagi hairpin feed point, and the line
>> isolator at the input to my amplifier,  between it and the Orion II.
>>
>> Seems to work well with all the radios here.
>>
>> 73,
>>
>> Mike
>> W2AJI
>>
>> Sent from my iPhone
>>
>>> On Jun 1, 2014, at 12:42 PM,k4elo at fastmail.fm wrote:
>>>
>>> Disagree Bob.  Put the choke at the feedpoint of the antenna or your
>>> coax will be radiating rf all the way down to the rig.  If you can't
>>> move the antenna, this is the most effective rfi fix.
>>>
>>> 73
>>> Wayne
>>> K4ELO
>>>
>>>
>>>
>>>> For starters,  as to RFI issues, yes antenna to radio spacing,
>>>> increasing same, will usually improve the issue.  Be sure all equipment
>> is each
>>>> bonded to a common point such as the PS ground.   Omit the external
>>>> ground but keep 3rd pin ground intact.   Use a common mode choke on the
>>>> output of the radio.
>>>>
>>>> 73
>>>> Bob K4TAX
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>> _______________________________________________
>> TenTec mailing list
>> TenTec at contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec at contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>
> Sent from my iPhone
>
>> On Jun 1, 2014, at 3:59 PM, "Rick - DJ0IP / NJ0IP" <Rick at DJ0IP.de> wrote:
>>
>> Mike is doing it CORRECTLY.
>>
>> My only comment is, the quality of the coax plays NO ROLE in this.
>> CMC flows on the outside of the coax shield so it makes no difference if 
>> you
>> are using the best or the worst coax in the world - (as far as CMC is
>> concerned; of course you should use good coax for other reasons).
>>
>> 73 - Rick, DJ0IP
>> (Nr. Frankfurt am Main)
>>
>>
>> -----Original Message-----
>> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Mike
>> Schatzberg
>> Sent: Sunday, June 01, 2014 7:39 PM
>> To: Discussion of Ten-Tec Equipment
>> Subject: Re: [TenTec] Trading radios
>>
>> In my case the RF is radiated from my Yagi and the coax shield picks up 
>> the
>> radiation between the antenna feed point and the radio.
>>
>> With good quality cable, the center conductor is not radiating.  However,
>> the shield may indeed be carrying current.
>>
>> Stations with RFI often only experience interference with their 
>> directional
>> arrays with the antenna in a certain alignment with their cable.
>>
>> I use a 1:1 current balun at my Yagi hairpin feed point, and the line
>> isolator at the input to my amplifier,  between it and the Orion II.
>>
>> Seems to work well with all the radios here.
>>
>> 73,
>>
>> Mike
>> W2AJI
>>
>> Sent from my iPhone
>>
>>> On Jun 1, 2014, at 12:42 PM, k4elo at fastmail.fm wrote:
>>>
>>> Disagree Bob.  Put the choke at the feedpoint of the antenna or your
>>> coax will be radiating rf all the way down to the rig.  If you can't
>>> move the antenna, this is the most effective rfi fix.
>>>
>>> 73
>>> Wayne
>>> K4ELO
>>>
>>>
>>>
>>>> For starters,  as to RFI issues, yes antenna to radio spacing,
>>>> increasing same, will usually improve the issue.  Be sure all equipment
>> is each
>>>> bonded to a common point such as the PS ground.   Omit the external
>>>> ground but keep 3rd pin ground intact.   Use a common mode choke on the
>>>> output of the radio.
>>>>
>>>> 73
>>>> Bob K4TAX
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>> _______________________________________________
>> TenTec mailing list
>> TenTec at contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec at contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
> 