Re: [IRCA] Cable connectors

[Nick Hall-Patch <nhp@xxxxxxxx>]

I believe that Gordon's low capacitance cable might also have been needed to reduce the capacitance seen at the output of his FET loop amplifier, otherwise it would be more prone to oscillate.   

My old NRC antenna reference manual, says that the feedline was used to eliminate "vertical effect".  I wonder if twinax or something like it would worked similarly?   The amplifier was meant to be attached to the balanced input of an R390A,  so it was important that one side of the balanced feedline didn't see more "vertical effect" than the other.   

Nick




At 00:11 9/7/2010, you wrote:

>---- Russ Edmunds <wb2bjh@xxxxxxxxx> wrote: 
>> I seem to recall that 'back in the day', Gordon Nelson was concerned about keeping the feedlines from his loops as short as practical for the application. Realizing that his recommended feedline was car radio cable with the original center conductor removed and replaced by insulated #22 or so ( with the braid soldered together on each line about every foot ) I wonder if it is in fact possible to get what you're aiming for. 
>> 
>> I don't recall the specific electrical and/or magnetic characteristics of that type of feedline vs. coax, but perhaps that too has some relevance here in that he eliminated using coax for a specific reason, which alas I also don't recall.
>> 
>> Russ Edmunds
>
>The only thing I can think of would be to lower the capacitance (per foot) of
>the cable itself. This is the reason that type of cable was spec'ed for
>car radios which had a compression trimmer that had to be peaked (at 1400 kc)
>for the specific car whip being used. Now that I think about it, real commercial
>grade coax contains spacers to keep the center conductor equidistant from
>all parts of the shield. Running in your own #22 wire for the center conductor
>after removing the original wire (I guess it was too flimsy) would lead to the
>wire being adjacent to the shield almost everywhere. Not sure how important
>that would be. I did that once, 40 years ago, but forget the details.
>
>- Bob
>
>
>
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*****************************
Nick Hall-Patch
Victoria, BC
Canada 

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