Andy,
Have you ever tried a near filed array ?
I think you where at the hfc ,eggham where on the Sunday morning there where
two lectures about loop type antennas, the first was quite fascinating, a
near field array, and the second was on contemporary loop arrays ...
I made a near field array based on the 'spirit' of the lecture .. and it
worked very well .. how it worked ive no idea .. but work it did .. made
from ? well
1 plastic dust bin as support ,
one standard alloy no-entry sign (round alloy)
3 feet vacuum cleaner plastic pipe (no spring) , as spiral former
1 sheet perspex as insulator
lenght of cotton covered 1.5 mm copper wire
earth tag and screw
wind wire on plastic pipe, bend into circle , place sine on top of bin ,
pespex on top of sine , place coil on plate, mount earth tap by coil end,
connect -one- side of feeder (i used 450 ribbon) to earth tag, connect
other side to -one- end of coil 'only' take feeder to tuner .. (1Kw racal
auto)
place assembly in middle of lawn ... Retire to safe distance
select frequency tx on , await atu lock, increase power to 400w carrier
and observe no flashover .. check from 1.8 > 30 mhz
find array functions on all bands .. work south coast on 1.8 mhz deep into
eu on 3.8 and mid russia on 28 mhz
Await Howells of laughter when you describe the antenna system ..
The step change to the previously published system was the concept of a
mirror .. so the coil is not counter wound .. and dose not flash over..
I keep looking for a bigger round alloy disk to try one on 500 .. i pass a
few on the way to work each day hihi
73 G ..
--------------------------------------------------
From: "Andy Talbot" <[email protected]>
Sent: Friday, December 05, 2008 7:05 PM
To: <[email protected]>
Subject: Re: LF: Re: E field active antennas
If you'd bothered to read the post, you'd have seen it was for a work
related task where we want a broad band active Rx antenna for the
whole HF band..
Can you tell me how to get any other sort of antenna that will allow
the whole HF band to be covered, in real time at high speed.?
If you can, and it works on high power Tx as well, then you've solved
the holy grail and stand to make millions of pounds!
Contrary to Mal's all pervading wisdom in all things RF related, a
long high tuned piece of wire is not the answer to all radio problems.
Oh, and a loop is no good, any directionality is a definite no-no.
If project funding permits, I may try an active horizontal loop in
addition. A 0.5m diameter loop into a broadband, balanced, common
base amplifier with Zin < 0.5ohms ought to give a reasonably flat
horizontally polarised omni directional HF band Rx coverage for
skywave signals.
Andy G4JNT
www.scrbg.org/g4jnt
2008/12/5 mal hamilton <[email protected]>:
Try a piece of wire as long and high as possible and an ATU this is
superior
to any active antenna or loop for that matter, the loop only helps in a
noisy environment, and even then not always.
G3KEV
----- Original Message ----- From: "Andy Talbot"
<[email protected]>
To: <[email protected]>
Sent: Friday, December 05, 2008 4:22 PM
Subject: LF: E field active antennas
Having just had to make an active antenna for HF (for gainful
employment-type work, not Am. radio purposes. The commercially made
one we've ordered is on five weeks delivery and it was needed before
yesterday) I was wondering about a helical element.
As the thing had to be resonably lightweight, I made the antenna
element from copper tape on 15mm plastic water pipe rather than use a
solid copper tube. Just for a bit of novelty I wound the tape in a
helix, but then started wondering if doing that would make any
difference to performance. Normally, helically winding an antenna
(rubber duck type at V/UHF) only serves to distribute loading
inductance into a short antenna to make it resonate - unlikely to
change improve the loss terms at all. But I did wonder if the added
extra inductance, or increased conductor length (not element length -
that is 1.2m) would change the performance significantly from a
straight tube.
Does anyone have any ideas - food for thought if nothing else? The
base amplifier is one I've used several times before for V/LF up to HF
based around a J310 source follower running at 20mA with bootstrapped
input followed by a 2N5109 emiter follower at Ic = 80mA. I may have
published it way-back-when in the amateur press in the 73kHz days.
Not the best design judging by some of those published in more recent
years, but did mean all the components were to hand for an instant
job.
Andy G4JNT
www.scrbg.org/g4jnt
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