Icom ALC Overshoot

[VK2NB]

Hi to the forum

I am looking at purchasing a 1296MHz transverter to operate on that band, I have a Icom 7000 and 7100 radios that I have had for some time and used as both base and mobile with no problems. The transverter requires a 144MHz if and the Icom radios will accommodate that requirement
These radio have been used without a linear, and I have herd about the Icom overshoot issue but to be honest never worried about it.
My question is, will this be a potential problem when using these radios with a transverter? I can wind the power right down but the transverter will only accept a maximum of 2 watts.

I am after opinions  as I dont want to over drive the transverter and damage it, I would be operating  both fm and ssb.

Thanks in advance

Nigel VK2NB

[VK4ADC]

I run transverters on my IC-706 series transceiver and have turned the output power back using the RF Power adjustment and haven't (yet) damaged any of my transverters.  My preferred method for power control - and used extensively by me in the past - has been to put an external negative voltage on the ALC connector pin and use a potentiometer (/trimpot) to set the actual applied voltage.  The required voltage for my radio has been about -3V so a zero to -5V is supply adequate.

The setup process is to set the RF Power to say 2-3 watts without the ALC connection in place, then connect the negative ALC control voltage and adjust the RF power to 1.5-2 watts.  (Ideally you set it to -5V first and reduce the voltage and see the output power rise to 2W.) That means the external voltage actually controls the output power regardless of whether you remember to reduce the RF Power setting next time around and whether ALC overshoot or undershoot actually occurs.

You can get the negative voltage from the likes of an ICL7660 voltage generator IC plus a few extra components (a 5V 3-terminal 100mA (or more) regulator plus a few electrolytic capacitors  and a trimpot to set the output voltage) but here is the key point : the negative voltage generator is powered the whole time, both on transmit and receive, and connected to the ALC control pin the whole time. 

Have fun on 1296 !!

[VK2NB]

Hi Doug

Thanks for that feedback I have looked up various informational re the voltage generator ic and will go from there.

73
Nigle VK2NB

[VK6RO]

VK2NB.. were you VK6NB  and a member of HARG a few years ago?

I think you were involved in data cabling etc when in perth?
vk6ro