[ICOM] AT500 problem on 18 and 24 Mhz

[Bert Almemo]

Hi Adam and Frank,

Thanks for reply and suggestions. After having a look inside I realize that
there is no connection between ANT1 and ANT2, That means that the Windom
antenna was never connected when I switched to 18 and 24 Mhz. I worked on
the yagi with bad results!

 So how do I get the windom on ANT2 connected to the switch position 21 and
28? Is it as simple as just putting in a jumper from ANT1 to ANT2 or...?
Probably not as the yagi and the windom work on the same bands between 14
and 28 Mhz. This is confusing?????? I guess it's a problem because I have 2
antennas sometimes resonant on the same band. I probably need an external
antenna switch. Strange design of a tuner!!

Any suggestions are highly appreciated. Thanks.

73 Bert, VE3OBU



-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Adam Farson
Sent: Saturday, January 07, 2006 2:06 PM
To: 'ICOM Reflector'
Subject: RE: [ICOM] AT500 problem on 18 and 24 Mhz

Hi Bert,

The Icom 0 ~ 8V band-selection voltage is ambiguous. 18 and 21 MHz share one
voltage value; 24 and 28 MHz share another. As a result, the AT-500, AT-100
and AT-150 share preset positions for 18/21 MHz and 24/28 MHz respectively.

A good way around this is to calibrate the AT-500 with a 50-ohm resistive
load on 21.2 MHz, and adjust the preset pots until the 4 LED's are dark.
Then, calibrate in the same way on 28.5 MHz.  Check on 18.11 and 24.93 MHz
to verify that the tuner matches the dummy load at these frequencies,

Check again with the antenna on 21.2 and 28.5 MHz; the reflectometer in the
tuner will detect any reflected power, and cause the tuner to re-match.
(This assumes that antenna SWR < 3:1 at these frequencies).

Now, when you select 18 or 24 MHz, the tuner should match the antenna
(again, assuming VSWR < 3:1). You may need to recalibrate the presets with
the antenna if the AT-500 capacitors are too far out of range when you
change bands, or recalibrate on a lower 15m and/or 10m frequency with the
dummy load.

An alternative is to start by calibrating the AT-500 in midband on 18 and 24
MHz with the dummy load. 

Cheers for now, 73,
Adam VA7OJ/AB4OJ




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