[Icom] Greetings - AH4 question

Sat, 21 Sep 2002 11:42:01 -0700

Hi Brian,

Firstly,  the transceiver's internal autotuner must always be disengaged
when driving an external tuner. Cascading tuners can reflect high reactance
values back into the auto-tuner and/or LPF. As a result, dangerously high RF
voltages can appear across capacitors in these networks, leading to
component failure.

If the AH-4 is presenting a grossly mismatched load to the IC-746, there may
be a fault in the AH-4, or the AH-4 is unable to tune the antenna connected
to it. A random-length antenna connected to that type of coupler may not be
a half-wave at any operating frequency.

The AH-4, AH-3, AT-120 and similar couplers key the transceiver via a line
which causes the transceiver to put out a 10W tuning signal. As far as I
recall, the tuner will not dynamically retune if load impedance changes
whilst transmitting (I may be wrong on this). The AH-4 will not tune if the
RF input power is less than 5W.

Here is a website which may be helpful:

http://www.hamoperator.com/ah4/ah4.htm

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Note new e-mail address:
mailto:[email protected]

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Brian Carling
Sent: Saturday, September 21, 2002 11:11
To: [email protected]
Subject: [Icom] Greetings - AH4 question

Hello Icom-ites!

I am new to the list here, and have a question.

I had read some of the reviews on eHam.net where they talked about using the
AH4 tuner.

A few of the guys use them with the IC-746.

I have an IC-746 here, and got the two working together, but I have a lot of
questions.

The tuner inside the IC746 retunes every time you change bands and takes
several seconds at full power.

Does the AH4 ever get to do its "350 mW tuning?"

Also, I notice that the SWR  back to the 746 appears to usually be about 5:1
or at
best 3:1 on 30m as shown on the SWR bridge in my MFJ-949D.

Now the 746 always manages to tune out that SWR, but am I losing power
anywhere with such an arrangement?

I have more questions but will see what comments and responses this brings.

Thanks everyone.

Brian ,AF4K