[Icom] AH-4 malfunctioning...

Tue, 11 Jun 2002 12:39:03 -0400

George,

The thing is...  It worked FINE, till.... he got water into the tuner..

Jerry
W3CDE

-----Original Message-----
From: George, W5YR [mailto:[email protected]]
Sent: Tuesday, June 11, 2002 11:42 AM
To: [email protected]
Subject: Re: [Icom] AH-4 malfunctioning...

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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