[NJARC] Antenna Feedline question

[Al Klase]

Hi Scott,

With vintage gear having pi-network outputs, the difference between  
50-ohm and 75-ohm loads should be entirely trivial.  I'd go ahead and 
build the antenna with the RG-6 because it's cheap, low-loss, and 
available.  I'd use F-connectors on the cable and adapters to connect to 
whatever else.

RG-6 might not support the HT-41, but worry about that later.

I hope the trapped design is worth the effort.  The traps themselves 
could prove problematic at high power levels.  You'll need good 
high-voltage caps in them.  There a lot of simpler ways to skin this 
particular cat, especially if you have an antenna tuner.

Good luck,
Al



Scott Roberts wrote:
> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Gentlemen(and ladies), I direct your attention to the ARRL 2008 "Handbook for Radio Communications", page 22.19
>
> I am currently building the W8NX Multiband, Coax-Trap Dipole"  for 10, 15, 20, 40 & 80M, as this seems to be one which will work for my needs, given the limited (attic) space available, and no trees nearby. I have most of the parts together, and am finishing building the traps.
>
> My question is about the feedline- My Hallicrafters equipment is specifying RG-8, and 50 ohm output: the antenna specs call for 75 ohm through a balun.
>
> I am planning to use a coiled coax balun, (P.21.16, Tab. 21.4) going in, but am still not sure what cable I can use. I was planning to use Radio Shack RG-8 (13AWG Type CL2 E111378A RS#278-1312) which I have a reasonable amount of for this exercise.
>
>  My other options would be RG-6(I don't have the spec# handy) CATV wire for the aerial drops(I have almost a full spool of this stuff in storage, complete with support wire attached) which has dual shielding & is also gel filled(for moisture prevention), or Radio Shack RG-58 coax.
>
> I think the RG-8 would be ok, as that is what the equipment calls for-
> What would I be suffering should I use that? The RG-6 seems to have the 75ohm the antenna calls for, however...
>
> I am going to get back to the build and set-up, but am hoping someone can help with this question. I am trying to get the antenna in this weekend, since I have had time to concentrate on radio stuff for a change, and want to get the HF gear ready to go! My max power available (once I find tubes for the HT-41) will be 1500w, although the HT-37 is 300 without it.
>
> As a side note, I built the simple groundplane(for 2M & 70CM) from pages 22.56 & 22.57, and it seems to work quite nicely. :)
>
> Thanks!
> Scott
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/