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Silver rod (what is the best antenna system option, isolate mast or not?)

Posted: 23 May 2020, 12:19
by InTheClouds
To the antenna experts....I have a silver rod which I can put on aluminium poles 3 - 6 of them, no radials and from today onwards an ugly balun (RG-213 6 turns 4inch pipe). As a "best I can do" situation should I isolate the silver rod from the mast or leave it non isolated from the mast? Just wondering what the most likely best scenario would be. Thanks

I cannot have any ground planes as they are impractical.

Re: Silver rod (what is the best antenna system option, isolate mast or not?)

Posted: 23 May 2020, 15:40
by Mudslinger
From what I gather an end fed antenna is only half an antenna and that to work correctly they need a counterpoise. That is either the mounting pole or the coax.

Personally I never bother to insulate and I have not had any issues.

Re: Silver rod (what is the best antenna system option, isolate mast or not?)

Posted: 23 May 2020, 16:48
by wa10
Good question, do you know anybody good with EZNEC that could model it for you ?

generally speaking you can't properly isolate an end-fed without giving it somewhere for return currents to flow,
you could make a proper isolator as long as you like, make the whole mast fiberglass then wind your choke, at the antenna,

that won't work, the current must return on something in order to have current entering the radiator,

currents inside coax are always equal magnitude & opposite phase whatever enters the radiator must return in equal measure on something, nothing you do can change that,

if all you have is coax with a choke the choke won't work as it should, voltage rises & equal current flows keeping Kirchhoff happy,

but you do have something that will carry return currents on that antenna, the bracket,
if everything else was isolated or not there in the first place it would have to flow on the bracket,

some say a 1/2wave end-fed is so high end impedance that little current flows & a very short radial is all that's needed,
i don't think that's true with fat pipe radiators or thick wires in radomes, if it was true nobody would have cmc issues with no radial end-feds,

i think it may be difficult to choke the coax off effectively with only the bracket for return currents, its worth a try, a choke won't hurt unless your unlucky & resonate the coax outer braid with it,

so your left with mast & coax. which would you least like to be radiating & picking up noise if you have to make a choice ?

if it was me id find a way to have small radials & isolate the antenna choke coax,

failing that let the mast do its thing & choke the coax, but if it runs down the mast it can couple back in bypassing the choke,

or just hope you pick a lucky length mast & coax length, people don't realise they have a problem unless its biting them in tha ass or lips.

Re: Silver rod (what is the best antenna system option, isolate mast or not?)

Posted: 23 May 2020, 20:35
by InTheClouds
Thanks, small radials may be a possibility, just not in the tree. They actually ship with very small radials as you can see in my avatar. However even those won't work in a tree they just stop the antenna going through the branches. I only put it up temporary and I have decided I am knocking it on the head until I can do static mobile now because my noise floor is terrible, it makes it pointless just to barely hear someone 5 miles up the road. I may be able to make some thick copper wire radials and just raise them up when out.

Re: Silver rod (what is the best antenna system option, isolate mast or not?)

Posted: 23 May 2020, 21:09
by The Collector
Try isolating any mast or bracket you have then if you've got a load of local noise and try it first with it totally isolated. If that doesn't help then you may be stuffed. It may be that you've also got some PLT issues that are driving up the white noise and general mush.

Before giving up though you can try using the 3 bolt-holes from your little ground-plane legs, bolt on 3 lengths of 9ft long, insulated wire, so they simply hang down like jellyfish tentacles. Tape the ends in case they make contact with anynpole you're using. The wire shouldn't get stuck in the branches as you raise the aerial up in the tree. If you can splay the wires out at an angle afterwards then even better, but I appreciate you may not be able to climb up that far.

I'm no expert and sometimes I think you have to just "suck it and see" with regards to aerial set-ups.

Re: Silver rod (what is the best antenna system option, isolate mast or not?)

Posted: 24 May 2020, 10:35
by InTheClouds
More food for thought thanks. The noise floor I believe anyway is not antenna self noise, silver rods are pretty quiet usually less so than an I-Max/Antron in my experiences. It is domestically generated I am sure. I don't suppose I am in the minority either, urban dwellers are often plagued by it. The garden tree is impossible to get any type of GP on there without more hassle than it is worth. Lost count of the times I have tried and just had terrible flickering noise S7+.

Re: Silver rod (what is the best antenna system option, isolate mast or not?)

Posted: 25 May 2020, 09:48
by wa10
something to consider is a gainmaster or T2LT for ease of isolating without radials, not sure how a dipole will perform stuck in a tree though,

one of my locals just converted a sirio 827 into a 1/2wave dipole, he's well travelled down the a99/imax/sirio gpe & 827 road & homebrew 5/8 with full size radials no radial 1/2 & 5/8waves,

theres was no conventional style cb antenna that he has not used & made his own version of, apart from an antenna that cb advertising claim has the lowest gain of them all,

He hates radials because birds **** from there on his house & path,

after some discussion about noise cmc & isolation without radials he took a hacksaw to the 827 radiator & converted it into a 1/2wave aluminium T2LT,

at the same tip height it performs at least as well as when it was dressed as a 5/8wave howling bird toilet & less noise than no radial end-feds for his situation,

you could make a coax T2LT to experiment with noise & leave it in the tree with a connector down where you can reach to hook up your coax,
costs next to nothing to try & less visible than a tube, if it works for you convert the silver rod into a dipole,

hope you get something you can use, noise is very frustrating.