AH4 tuner in the middle of an offset fed dipole
Allan Jeal
even arguments ....
Is it likely to damage an Icom AH4 auto antenna tuner if the "antenna"
terminal is attached to one leg of a V (resonant at 14Mhz) and the earth
terminal is connected to the other leg of the V (resonant at 7Mhz) without
any additional grounding. Is there any reason to swap the legs around.
Assume 100 watts max. It would be helpful if any opinions came from those
who are familiar with the internals of the AH4. It would also be helpful if
any repondents understood that others could have a differing opinion. de
VK2DQC, Allan. tnx
Bob Miller
If you do a Google search for the AH-4 -- there used to be someone
with a page that showed it hooked up to a dipole, using the ground lug
for one of the dipole elements.
bob
k5qwg
Cecil Moore
Is it a 48 ft. dipole off-center-fed 16 ft. from the end?
If so, what do you seek to gain by off-center-feeding it?
--
73, Cecil http://www.qsl.net/w5dxp
Bruce in Alaska
Bob Miller <NOS...@neosoft.com> wrote:
I have used similar setups in commercial service all over alaska.
We used SEA1612B Autotuners feeding twin Morad 2600 Loaded whips
in a dipole configuration. The only caviate that I would put out
is, that you might think about decoupling the Coax Feedline and
Power Leads by wrapping them in bifilar fashion on a suitable
torriod core. The above systems are still in use 15 years later,
and doing just fine on frequencies from 2.0 Mhz all the way up to
26 Mhz. the other thng that you must figure on, it that these type
of antenna tuners can't tune the 1/2 Wave Resonante Frequency of the
connected antenna. So, one must carefully consider just where the
1/2 Wavelength Resonance Point is, and place it in a portion of the
spectrum that your not going to want to transmit.
Bruce in alaska (AL7AQ)
--
add a <2> before @
Allan Jeal
exciting New Year riding around on your magnificent Harley)
The reasons for the particular configuration that I am playing with were
originally clear but have become a little fuzzy over time. My aims are to
make an antenna that is 1) transportable 2) light weight 3) ground
independant 4) to be erected on a caravan in various caravan parks without
upsetting everybody 5) quick to set up and pull down 6) gives me a few bands
to play with 7) possibly even work to some degree !
After trying verticals, loops and dipoles I was ready to give up. Then I
remembered a thing called a Vipole that was lying on the garage rafters. I
paid hundreds of dollars for it but I could never make it work. It is a V
with two lightweight fiberglass whips that each have an inductance coil half
way along their length. They are marked 7Mhz (12' roughly) and 14Mhz (9'6"
roughly). (((The original design stipulated that the whips feed into a Balun
and then an UnUn transformer, and then use coax down to the rig))).
Anyway, I guessed that I could use the two lightweight whips - still in a
Vee configuration. I decided to dump the Balun and the transformer and
replace them with an auto tuner that I had lying around. So, now I have the
first five criteria - all I have to do is make it ring on a few bands
without smoke signals. So far it appears to receive well but I have serious
doubts about its radiation properties (if any) - time will tell.
Allan
"Cecil Moore" <myc...@arrl.net> wrote in message
news:Wybtf.38937$dO2...@newssvr29.news.prodigy.net...
Allan Jeal
glad that you made the point -
> of antenna tuners can't tune the 1/2 Wave Resonante Frequency of the
> connected antenna. So, one must carefully consider just where the
> 1/2 Wavelength Resonance Point is, and place it in a portion of the
> spectrum that your not going to want to transmit.
I beleive that this same note is made in the AH4 documentation, thanks for
the reminder, I'll look back at this. I'll also consider your thoughts re
decoupling. And thanks for the tip on the Google search. I have actually
tried the search on Google but may have been too quick to give up. Will do
it again.
Cheers and have a great New Year
Allan
"Bruce in Alaska" <bru...@btpost.net> wrote in message
news:bruceg-E1B2D9....@netnews.worldnet.att.net...
Owen Duffy
<allan...@hotmail.com> wrote:
...
>Is it likely to damage an Icom AH4 auto antenna tuner if the "antenna"
>terminal is attached to one leg of a V (resonant at 14Mhz) and the earth
>terminal is connected to the other leg of the V (resonant at 7Mhz) without
>any additional grounding. Is there any reason to swap the legs around.
What you intend doing will connect the "ground" rail of you tuner to
one side of the antenna, and unless you take other steps, the "ground"
rail of the tuner will be connected to the radio chassis via the coax
outer and the control cable. Perhaps the radio will be connected to
ground directly or indirectly.
This is not a lot different to feeding a dipole without a balun
(whether by coax or open wire line).
You might be concerned about whether the likely RF common mode
currents will disrupt or damage the control interface at the radio or
tuner.
There have been lots of reports of people doing what you propose, some
choke common mode currents below the tuner, sometimes with separate
chokes on the coax and control cable, some choke common mode currents
above the tuner, sometimes providing a local ground to the tuner, and
some do nothing.
I favour a choke above the ground mounted tuner, and a local ground on
the tuner to help to reduce the rf currents flowing on the coax and
control cables into the shack. I have done this with open wire feed
above the tuner to the dipole feedpoint and it worked fine without
noticeable "RF in the shack" problems.
I note that SGC is now producing an auto-tuner with balanced output,
but have no experience of its performance.
The main issue that I see with these tuners is the difficulty of
diagnosing faults and identifying faulty components for replacement,
and it makes me think twice about investing in them.
Owen
--
Cecil Moore
> After trying verticals, loops and dipoles I was ready to give up. Then I
> remembered a thing called a Vipole that was lying on the garage rafters. I
> paid hundreds of dollars for it but I could never make it work. It is a V
> with two lightweight fiberglass whips that each have an inductance coil half
> way along their length. They are marked 7Mhz (12' roughly) and 14Mhz (9'6"
> roughly). (((The original design stipulated that the whips feed into a Balun
> and then an UnUn transformer, and then use coax down to the rig))).
OK, I think I've got it. Although the autotuner will probably
tune the system, the 20m element will probably be an inadequate
counterpoise on 40m and the 40m element may develop a lossy
self-resonance below 14 MHz. A 40 ft. dipole with the tuner
in the middle would probably outperform what you have in mind.
But that's just my opinion which is what you asked for. Don't
let me discourage you from experimenting.
Allan Jeal
would outperform it - but I have to keep it within the criteria:
1) transportable 2) light weight 3) ground independant 4) to be erected on a
caravan in various caravan parks without upsetting everybody 5) quick to set
up and pull down 6) gives me a few bands to play with 7) possibly even work
I will take Owen Duffy's advice to reduce RF getting back to "the caravan
shack", then continue to experiment. At this stage it seems to receive very
well, but waiting to get answers to my CQDX.
73 de VK2DQC "portable anywhere in Aus."
"Cecil Moore" <myc...@arrl.net> wrote in message
news:TQmtf.40378$7h7....@newssvr21.news.prodigy.com...
Allan Jeal
VK2DQC
"Bruce in Alaska" <bru...@btpost.net> wrote in message
news:bruceg-E1B2D9....@netnews.worldnet.att.net...