[Icom] AH-4 malfunctioning...

[Demetre Koumanakos]

Hi George,

Thanks for the reply, all about the antenna ground I'm aware of, but 
there was no real direct ground installed before we moved in our 
house and there is no way I can install an ideal ground at this point.
I'm located in the northern subburbs of Athens at the foothills of 
mount Penteli where the soil is far from ideal for a good ground.

The tuner itself has not been damaged by water and has been working
efficiently for 3 years now. There are other vertical antennas near
by (about 10 meters away) but in general the setup hasn't changed 
ever since the tuner was installed.

A rotatable loop has been on the drawing board for some time now, 
I'll most probably complete and install this summer. I suppose due to 
the fact that it doesn't require a ground and the 2db gain (over a 
dipole) it will outperform the vertical.

Anyway thanks for your help, BTW Athens has changed a great deal 
since 1952 (I was -10 years old at the time hihi) and will be a good 
visit in 2004 with the Olympics.

73
Demetre - SV1ENS


> Demetre, I would be inclined to suspect the integrity of your
> "ground" connection. The clue is that you describe a "direct
> ground connection about 10-15 meters from the ground  . . ." Any
> conductor of that length is far from a direct connection at r-f.
> It has an impedance which varies with frequency and its effect
> will depend upon the nature of the "ground" connection you have to
> Mother Earth.
> 
> You describe an antenna element some 33 ft long connected to
> "ground" via another wire about 35 feet long. At the feedpoint of
> the antenna system you have your AH-4 connected to the driven
> vertical antenna element and to the other feedpoint which is the
> wire to "ground" plus the several radials on the roof.
> 
> If I am visualizing this system properly, it seems to me that the
> wire from the feedpoint to earth ground is (a) probably
> contributing little if any useful radiation but still is carrying
> r-f current, and thus radiating, on some bands which can be a
> source of RFI, etc. While this power is being radiated, it is not
> being radiated from the "antenna" which is your goal.
> 
> That wire is just as much as part of your antenna system, at least
> on certain bands, as the radials and the vertical element. The
> presence of the radials helps to collect return current in the
> vicinity of the feedpoint but does not prevent some current flow
> in the wire to "ground."
> 
> I keep using "ground" because unless your have an absolutely solid
> r-f connection to Mother Earth, which is very difficult to obtain,
> there is no telling what the impedance to actual ground of the
> wire - viewed at the feedpoint - really looks like on the various
> bands. It is almost a certainty that it is non-zero and that some
> current flows in the wire on some or all bands, just as current
> flows in the radials on the roof.
> 
> If the connection were valid, on any frequency where the wire is
> an odd multiple of a quarter-wavelength, it presents a high
> impedance at the feedpoint and is effectively disconnected and
> "not there." Conversely, where it is an even multiple of a
> quarter-wavelength it effectively places earth ground at the
> feedpoint, a condition which I gather you are attempting to obtain
> on all bands and may have achieved on some. However, note that the
> effect of the wire is highly dependent upon frequency. Unless you
> happen to be operating on a frequency where the wire is series
> resonant - the odd quarter-wavelength condition - then it presents
> a complex impedance and offers another path for r-f current.
> 
> Bottom line: I suspect that the variability of your tuning, etc.
> is being caused by varying integrity of your "ground" wire
> connection and possibly other aspects of the wire's surroundings.
> I would strongly suggest that you disconnect that wire from the
> feedpoint, remove it completely if possible, and reevaluate the
> operation and performance of your system to determine if that
> indeed is the culprit. Just disconnecting it is not enough since
> it would otherwise still be in the immediate induction field of
> the antenna and be coupled as part of the system.
> 
> A fact to remember: there are no switches on antennas or wires in
> the immediate vicinity of an antenna. Just because they are not
> electrically connected does not mean that they are not present and
> having an effect. For example, consider the parasitic elements in
> a Yagi array . . .
> 
> You may have installed the wire originally to provide a ground
> path for possible lightning strikes, etc. or you may have intended
> to make a "ground" connection for the tuner. I seriously doubt
> that a single wire of that length would afford much if any
> lightnihg protection, especially if it terminates in a
> questionable connection to Mother Earth. A single ground rod
> driven into the soil will be almost totally ineffective either as
> a lightning protection measure or as a means for providing an r-f
> "ground" connection.
> 
> I hope that you can find the cause of your intermittent operation
> quickly and easily. I would certainly start by disconnecting and
> preferably removing the wire from the feedpoint to the "ground"
> connection. While a loop might provide better operation for you,
> especially if its use requires removing your "ground" wire, I
> suspect that you can continue using the vertical by taking only
> that simple step.
> 
> Good luck!
> 
> BTW, I operated SV0WB from the Tamion Building in Athens in 1952
> while in Greece as a Tech Rep for RCA . . .
> 
> 73/72/oo, George W5YR - the Yellow Rose of Texas
> Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
> Amateur Radio W5YR, in the 56th year and it just keeps getting
> better! QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
> I-LINK 11735 Icom IC-756PRO #02121  Kachina 505 DSP  #91900556 
> Icom IC-765 #02437
> 
> 
> Demetre Koumanakos wrote:
>> 
>> Hi Clete,and all who replied...
>> 
>> My AH-4 tunes a vertical element (10 meters long) with a direct
>> ground connection (about 10-11 meters from the ground) and a
>> number of 5 and 10 meter long radials randomly laid down on the
>> roof of my house.
>> Up to about a week ago the tuner tuned from 3.5 to 50 Mc with no
>> problems, this past Sunday it refused to tune anywhere but 14 Mc.
>> Yesterday on my bench it seemed to work fine tuning all bands
>> again, once on the roof it lost 80m again.
>> I can probably live without 80m but not knowing what the heck
>> makes it malfunction is driving me crazy...
>> 
>> For some time now I've been thinking of replacing the vertical
>> element with a rotatable large loop verticly polarized for 40m.
>> in theory the AH-4 can tune this arangement also.

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