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G0FTD > ANTENA 27.12.04 08:44l 123 Lines 4713 Bytes #999 (0) @ WW
BID : 7C9102G0FTD
Read: DG8DG DG5YM OE5AKM GUEST DL1NT
Subj: 80-6m indoor loop (revised)
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<7M3TJZ<ON4HU<ON0BEL<GB7CIP<
GB7SXE
Sent: 041226/1215Z @:GB7SXE.#38.GBR.EU #:17346 [Hastings] FBB7.00i $:7C9102G0FT
From: G0FTD@GB7SXE.#38.GBR.EU
To : ANTENA@WW
[Text slightly revising to clarify a few points]
[Text may be reproduced on any website or bbs]
A Simple 80m to 6m loop antenna that works DX (Slightly revised vesion).
Here is a brief description of my simple antenna which is in my bedroom
shack !
A 2.4mý wire quad loop is literally "drawing board pinned" to the brick
wall. The ATU is a T-Match that I've had for nearly 25 years and there is
nothing special about it at all except that it does use a roller coaster
inductance which can help minimise losses. The exact size of the loop is
not critical. I suggest a minimum of 2.4m each side to perhaps 3.2m.
The 1:1 balun was made from some scrap enamelled copper wire (18SWG) and
a 3 inch piece of ferrite rod stolen from a dead broadcast receiver. The
balun is shown as B1 in the diagram. It is fitted into my ATU so that
there
is NO coaxial interconnecting feeds.
This is important.Under NO circumstances should the interconnections be
made by lengths of coax.
On 24.9Mhz/28MHz you either operate the antenna as:
A normal quad loop with no inductance (short it out) or with the
inductance
in line which makes the radiation pattern swing around.
The 100æH air wound inductance is used on 24.9Mhz and 28MHz to swing the
radiation pattern around by 90ø however the polarisation will change from
horizontal to vertical.
On all other bands there is no use for the inductor, just short it out or
you can utilise it for impedance matching if you find your ATU is running
out of steam on some bands.
The antenna can be run without a balun but I have found that on certain
frequencies the transmitter sees conductors within the shack wiring and
surrounding cabling and induces imbalance which can effect performance.
It's easy to check for this problem,just try tuning the antenna whilst
touching the radio casing or atu casing and see if the SWR changes or if
your getting RF burns from your equipment. Any evidence of such problem
mean you really ought to use a balun.
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³ 100 æH ³
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³ 2.4mý square loop ³
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________________||_____________________________________________
\ \\ || \\\ bedroom floor upstairs \\ \\ \
||
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50ê COAX
Using totally indoor antennas has been a bit of a hobby horse of mine and
I've played with loops for some years now. This is just another variation
of a few I have been trying.
Losses through brick walls don't appear to be very great. In fact hardly
worth mentioning on HF. I tend to use QRP these days, it helps keep TVI
away as well as providing a challenge.
On 80m my best DX has been UZ7HO (I used 25 watts), inter europe on 40m
(10 watts),numerous european and Russian QSO's on 30m CW with 3 watts plus
South Africa,USA,VE and Brasil on the HF DX band using around 15 watts
SSB.
On 6m during the sporadic E season I can easily work around Europe with
3 watts CW and SSB.
Although I have experimented with the antenna on 160m I have yet to be
satisfied with the performance although it can make a few QSO's on
groundwave for about 30 miles.
If anyone has a way of improving 160m performance I'd be grateful ;-)
For me the advantage of this simple loop system means that it's CHEAP !
No expensive vacuum variable capacitors or heavy duty construction with
copper pipes.
I can work the DX without even having an outside antenna, with low power
and enjoy my hobby everyday.
There is NO excuse for complaining that you don't have space for an
antenna. The possinilitoes of young hams still at home can play on HF -6m,
apartment and flat dwellers, those without a garden or simply anyone
looking for a challenge.
So get cracking..
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ 73 - Andy ³
³ G0FTD ³
³ Whitstable, Kent ³
³ Winpack-AGW ³
³ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³
³ ³ Û ³ ³
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