[Icom] Greetings - AH4 question

[Brian Carling]

Well since this is the only comment on that web site about using the AH4 wth an 
IC746 I am not helped at all!

>>AH-4 Frequently Asked Questions (FAQ)

Please address all additions or corrections to K9EQ.

Q: When is the AH-4 in bypass mode? Is it in bypass mode when the power is off?

A: While it is possible to receive when the power to the AH-4 is off, the AH-4 is not 
directly connected to the antenna. It is necessary to have the power on to bypass 
through the AH-4 from the rig to the antenna. You can bypass by turning power 
off and on (without tuning) or by using the UNTUNE feature either on the Universal 
Interface or on the Icom radio. Because of the critical timing it is probably not 
possible to untune when using a manual push button.

Q: How long can you make the control cable between the radio and the AH-4?

A: I have run up to 60 meters (200 feet) of rotor control cable with no problems.

Q: What limits the length of the control cable?

A: Two factors. The IR drop (resistance) of the wire can limit the amount of power 
available to the AH-4. Plan on the AH-4 consuming one amp and requiring a 
minimum of 10.5 volts. The second factor is more difficult to determine. The AH-4 
communicates with the radio via two control lines. If these lines become too long 
and have too much coupling between the other lines, the rise time of the signal will 
not be sufficiently fast.

Q: How does the AH-4 differ from the AH-3?

A: The wiring is identical and I assume that the AH-3 will work where ever the AH-
4 will and visa versa. I did notice, however, that the 706 MKIIG implements some 
special circuitry just for the AH-3. It is not clear to me why this is done. The main 
difference from the user's point of view is that the AH-3 is specified to operate on 
160 meters, while the AH-4 eliminates 160 and includes 6.

Q: Can you use the AH-4 on 160 meters?

A: Yes and no. I do it with a "large" antenna. It will only cover a portion of the 160 
band or none at all depending upon the characteristics of the antenna. My 21 
meter flat top and the AH-4 cover the entire 160 meter band.

Q: I was wondering if there is a way to use it in Amtor/Pactor-II with a PTC-II 
controlling my IC-746 in Scan mode. Of course, the AH-4 would have to be in By-
Pass mode during Scan and ready to be tuned on the first TX on air pulse. Can 
this be done?

A: The AH-4 automatically drops out of tune mode when the radio changes bands. 
The trick is to get it to tune when you first transmit. This is an option on the 706 
and I assume other Icom radios. Simply select "PTT TUNE" from the initial set 
mode items. That way the AH-4 will tune the first time you transmit on a band. I 
have found that my AH-4 will generally cover the entire band and does not need to 
retune once it has tuned. This may vary with a different antenna.


It seems like no one knows much about the AH4.
I don't know if it's tuning at all, since ther eis no indication in the shack.

It plugs right into the back of the IC746 with a connector that is the same as on the 
IC-706.

Since two or three other fellows in the eHam.net reviews mention using it with the 
746, I assumed that SOMEONE knows what they are doing (he he!)

I will try to e-mail those guys if no one here knows what specifically should be 
done.

By the way, I am using buried coax as a lead in, and since the AH4 IS clearly 
doing SOMETHING that helps the tuning I don't see what I would do differently.

There is only one TUNE button on the 746. It keys the internal tuner.

How would i get it to only key the AH4 as you have suggested?