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Latest Buxton 2021 New date, now 30th July - 1st August
Call Sign : 26-CT-4145 Posts : 90 Times Thanked : 1 Join date : 2021-06-03 QTH or Location : Chatham, Kent Equipment Used : Includes :- AT-878UV, FT474Gx, AT-5555N, FT-818, DNT M40 (RT Factory, Manpack config), Midland Portapack, IC-211E, TS700G, TS2400, MAXCOM 16E, unbranded 40 channel Japanese 49 & 2.4Ghz transceivers (supposedly Uniden, but unlikely) Age : 52
Subject: Quickly improving any detachable HH antenna . Tue Jun 15, 2021 7:38 pm
The biggest cause of reduced efficiency on HH antennas and ditto for fully shoulder or backpack manpacks is your usually electrically long and physically short necessary evil antenna and you.
The antenna itself has a dual issue, as do you - whilst a swop of a less restrictive antenna is the easy but not always practical fix, irrespective of how you handle that half of the equation, people fail to tackle the other half effectively.
Because of how we use such gear, we are a capacitive and inductive influence on the antenna's radiation pattern and a cause of some desensitization. In fact, our close vicinity makes us both inductive grounding and inductive part of the driven element in one fell swoop.
So the easy answer is to offset the antenna so it's portable enough for mobile use yet body influence free. If you've ever looked at a proper manpack antenna kit, it contains at least one or two non-conductive spacer sections and often at least a semi-dog leg example. There will be some conductive examples as well.
Taking note of that, often the missing bits of an incomplete ex-military kit are those offset pieces.
So have a look at photos of such kit, if you can't get to look at an example first hand and the rest will make sense :-
All you are really aiming for, irrespective of antenna type used, is to offset the position of the antenna vs you. Now a bit of repositioning at arms length tells you that moving the radio (as it's effectively a chassis ground radial) half an arms length above and away can make a huge difference vs desense and ultimately will reduce how much RF you actually absorb.
So, having experimented, go cut some plastic/polymer tubing to create the offsets pairing you figured out. Now you can find, since the offset is very short usually, that a socket on the uppermost end of offset to mate with antenna, feeding a coax run inside the tubing to another connector to suit the radio's ant socket is an adequate and tidy way to bond your offsetted antenna and it's loss factor should be far lower that caused by the original near-field proximity setup.
Having got it sorted, then find a way to structurally support the offset (so prevent any further undue socket strain) and it's job done.
It's how I use, pedestrian mobile, my FT and handhelds, so I know it's making a difference.