[Icom] AH-4 malfunctioning...

Wed, 12 Jun 2002 02:21:47 -0400 (EDT)

Hi Jerry,

Actually it worked fine for 3 years, and I *never* got water
in to the tuner...

73

> 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.
> ----
> Your Moderator: Dick Flanagan W6OLD, [email protected]
> Icom FAQ: http://www.qsl.net/icom/

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