When referring to 90 degrees I assume you mean perpendicular to the dipole wire
eh? Which means that an Inverted-V should always have a choke at the feed
point?
Eric
W9WLW
Sent from my iPhone
> On Jun 1, 2014, at 4:12 PM, "Rick - DJ0IP / NJ0IP" <Rick@DJ0IP.de> wrote:
>
> Jim, in my opinion it is not necessary.
> Until last summer I would have agreed with you.
>
> After spending about 200 hours in the field measuring this stuff, I did not
> find enough cmc on the coax of a dipole, "IF AND ONLY IF" the coax runs 90
> degrees away from the antenna, to bother worrying about. You need no choke
> or balun.
>
> As soon as you begin to bend the coax and run it at a less than 90 degree
> angle, the picture changes.
> Then you should place "something" at the feedpoint.
>
> At the feedpoint, I tried several different kinds of baluns and a simple 1:1
> Guanella choke.
> It made no noticeable difference what was at the feedpint, as long as you
> used something.
> I have EXACT MEASURED DATA for all of this.
>
> ALL tests were made running 100w from a Ten-Tec Eagle into the antenna
> system.
>
> However, I would ALWAYS recommend placing a cmc choke at the house before
> the feedline enters the shack.
>
> If the feedline is very long, then as Jim recommends in his "RFI Ham", I
> would insert one or more cmc chokes in the coax along the long run.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Jim Brown
> Sent: Sunday, June 01, 2014 8:21 PM
> To: tentec@contesting.com
> Subject: Re: [TenTec] Trading radios
>
>> On 6/1/2014 11:01 AM, Bob McGraw - K4TAX wrote:
>> If one chooses to use only one Common Mode Choke or Line Isolator,
>> best first placed at the radio.
>
> No, the first choke should be at the antenna feedpoint. W2AJI is exactly
> right. A choke at the radio would only matter if the shield of coax
> connector was not bonded to the chassis. So far, I've not seen a transceiver
> where this mistake was made.
>
> Now, an additional choke either at the radio or at some intermediate point
> on the line CAN be useful to the extent that it functions as an "egg
> insulator" for the common mode current induced on the line by a nearby
> vertical antenna, which makes it a parasitic element of that other antenna,
> modifying its pattern.
>
> And there ain't no such thing as a 1:1 common mode choke. A common mode
> choke is a straight through section of transmission line wound around a
> ferrite core. No transformer action. No turns ratio.
>
> In every radio I've looked at, the bodies are buried in the unbonded
> unbalanced jacks, not on the output SO239.
>
> 73, Jim K9YC
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|