ATU and Long Wire
Leigh Preece
I'm close to getting my UK RAE Morse ticket and have a Trio TS520 HF radio
(80 to 10m) but a very small garden - 60ft long but 15ft wide.
I currently use a random length long wire for a HF receiver but obviously
want something better when I get up and running with the HF TX.
Two questions:
1 - would a MFJ 16010 ATU and a long wire ran around the perimeter of the
garden work - upto about 75 ft in length ?
2 - Does a half size G5RV and balun (to make the full size equivalent) need
an ATU as it claims to work 80 to 10metres ? The MFJ 16010 says it only
works with random wire but I notice from reading on the WWW, that the G5RV
has an impedance of 50 ohms.
Would option No. 1 be a good way to start or could someone advise of a
better ATU that would work with either random wire or 50 ohm feeders ?
Many thanks in advance - replies email or to the group to get a good set of
post for others to see.
Leigh.....
M1CZK, UK.
--
Leigh M. Preece, Media and Communications Centre, Keele Univ. Staffs. UK
WARNING: My ONLY reply address is: le...@media.keele.ac.uk
Peter O. Brackett
I agree with Reg. The inverted L antenna is great for small gardens.
I used one successfully for several years from a small lot in an "no
antenna" neitghbourhood in South East Florida. It was essentially invisible
to the neighbours!
I ran the veritcal leg of the L up a tree trunk [actually hung from a
branch] and the horizontal top leg over to another tree. I simply cut the
length to fit the space, I never did know how long it was! I used a small
diameter wire which was essentially invisible to the neighbours.
As Reg points out however, to get out a good signal, an efficient ground is
essential!
I used an MFJ antenna tuner to load up the antenna. It seemed to load up
well on 4 bands. Even though my inverted L loaded up fine at first using
the antenna tuner with just a waterpipe ground plus a single ground rod, no
one could hear me well! I was about to give up on this antenna, and hamming
from that location for that matter.
But, I persisted.
And so . . .I supplemented my waterpipe ground with several 1/4 wave
counterpoises. What I did was cut [in my case three], 1/4 wave lengths of
enameled wire one each for each of the bands that I was interested in.
[e.g. one each for 40 m, 30 m, and 20 m.] and with them all soldered
together at the ground feedpoint of the invereted L, I simply strung these
out in the garden in whatever geometric pattern seemed to fit the lot and
obstacles. [i.e. along the foundation of the house, along the fence line,
etc.] None of the three counterpoises was straight, and they were only
hidden underground [by about 1/2 inch] where they crossed the open garden
lawn. Actually I installed these 1/4 wave counterpoises at different times
several weeks apart as I increased my operations from a single band over to
several bands.
With these counterpoises in use, the antenna not only loaded up just fine,
but also apparently radiated well. About 50 countries heard me 59 with that
antenna!
This is all just to take note of Reg's idea that the inverted L is great,
but . . . you might have to fool around a bit to get a halfway efficient
ground system.
Peter AB4BC
Reg Edwards wrote in message <01bea9aa$c3e43540$f3cbac3e@default>...
>Dear Leigh,
>
>For starters, just get the feel of things with an
>inverted-L antenna which fits comfortably into your back
>garden, fed against your cold water pipe + mains power
>earth + anything else which might provide a low impedance
>to ground. One earth rod is useless !
>
>The TS520 internal ATU (a pi-match network) will cater for
>a range of antenna input impedances. Cleanse your mind of
>such nonsensical 'old wive tales' as SWR. Tune up for
>minimum-dip on the anode current meter according to the
>operating manual and away you go.
>
>The odd tapped coil or variable capacitor in series with
>the antenna wire may be occasionally useful.
>
>Believe me, you will learn far more, in a few days, with
>this simple set-up than you will with 12 months messing
>about with over-rated G5RV's and very low, very lossy
>horizontal loops. Make your mind a complete blank about
>such things as 1/2-size G5RV's. Mr Varney will agree. You
>have been reading the wrong magazines.
>
>THEN, and ONLY THEN, being much wiser, you can start
>thinking about an antenna to suit your favourite band(s)
>which will fit into the space available.
>
>By the way - the most important back-garden
>characteristic of an aerial is its height, not shape.
>--
>******************************
>Reg, G4FGQ For free software go to:-
>http://www.btinternet.com/~g4fgq.regp
>
>******************************
>
>Leigh Preece <le...@media.media.keele.ac.uk> wrote in
>article <7ijrcp$r82$2...@cfs2.kis.keele.ac.uk>...
Reg Edwards
Alurk50
>With these counterpoises in use, the antenna not only loaded up just fine,
>but also apparently radiated well. About 50 countries heard me 59 with that
>antenna!
>
Good Answers Peter!
I'm loading up a dipole fed with 450 wire thru a MFJ tuner and it works
great.....but....I've heard much about the counterpoise thing and I'll be
adding one here too! However...feeding a dipole creates it own counterpoise.
Al KB1LI
Roy Lewallen
Roy Lewallen, W7EL
Robert Lay (W9DMK)
...snip
>I currently use a random length long wire for a HF receiver but obviously
>want something better when I get up and running with the HF TX.
Absolutely.
>1 - would a MFJ 16010 ATU and a long wire ran around the perimeter of the
>garden work - upto about 75 ft in length ?
I do not have a model 16010, but I am reading the specifications from
MFJ's catalog, and I assume from everything presented there, that it
is an "L" section matching device or "ATU", capable of either step up
or step down of impedance when properly used. From what I can see on
the illustration it uses a tapped inductor (left hand dial) and a
variable capacitor (Right Hand dial)
Based on that, I would say that it will give satisfactory results in
comparison with any number of more complex tuners, provided you are
willing to live with some lack of flexibility in comparison with a
full "T" matching section with its two capacitors. You will also need
some means of detecting a proper match. so we have to assume that you
have an RF Bridge or an SWR meter to use in conjunction with the "ATU"
Now we get to the issue of the antenna itself. I do NOT recommend a
long wire for two reasons.
1) it will require an equal amount of effort, if not more, in
establishing a good RF ground - either through an elaborate
counterpoise system or a combination of earth rod and buried radials.
2) it is unlikely to be as efficient as a dipole.
Since your garden has a perimeter of almost 150 feet, rather than run
the wire around as a long wire, make it into a loop, and make feed it
as a balanced antenna. Use 450 ohm ladder line from the feed point to
the tuner and install a balun at the tuner to transform from the
balanced line to a short piece of coax. Hang the balun outside the
dwelling, and run the short coax into the dwelling to the ham shack
and to the tuner. You can now tune for a match to 50 ohms on
practically any frequency that you choose between 1.8 MHz and 30 MHz.
>2 - Does a half size G5RV and balun (to make the full size equivalent) need
>an ATU as it claims to work 80 to 10metres ?
There is no such thing as a half size G5RV. Any length of "G5RV" that
is not per his original dimensions is simply a center fed Zepp. There
is also no way to use a G5RV over any significant range of frequencies
without an ATU - except perhaps on 20 meters. It does cover a
significant portion of 20 meters without an ATU, depending upon your
criteria for allowable SWR.
>The MFJ 16010 says it only
>works with random wire but I notice from reading on the WWW, that the G5RV
>has an impedance of 50 ohms.
On your first point - MFJ's wording should not be taken so
restrictively. The ad says "using a random wire and ...". That does
NOT exclude coax, etc. It only excludes a balanced feed line, because
they did not include a balun in the ATU. If you want to use a coax fed
dipole - no problem. If you want to add the balun and feed with ladder
line - no problem. In fact, that's what I recommend.
On your second point, that the G5RV has an impedance of 50 ohms -
that's rubbish. Whoever told you that is not to be trusted. There is
probably a single frequency (somewhere in the 20 meter band, where it
MAY approach something very close to 50 + j0 ohms, but that's a far
cry from saying that it "has an impedance of 50 ohms.