ALC Overrun


Algenon M0JIO
 

Hi Microwave Group 

I’m new to the forum and looking for some advice on what I believe is called ALC Overrun. I am looking at purchasing an SG Labs 1296 transverter to get started on 23cms. All the advice is to use an IF radio with a max output power of 5W. I would like to use my Icom-7100 with the power turned down to 5W as the IF radio but I understand that some radios can momentarily output more power than set  thus damaging the transverter. Does the group have experience of this combo and/or is there a way for me to detect if the radio does output momentarily in excess of the set power. I have basic test equipment: dummy load, power meter, 50Mhz scope which I suspect will not detect any blip. 


Andy G4JNT
 

Use a 50 ohm resistor as a load and connect a diode detector across it.  A 1N914 etc will suffice  .   Transmit from your rig into that and use the scope to monitor the diode voltage.   That should show any ALC overshoot.



On Thu, 8 Apr 2021 at 09:48, Algenon <alg_edwards@...> wrote:
Hi Microwave Group 

I’m new to the forum and looking for some advice on what I believe is called ALC Overrun. I am looking at purchasing an SG Labs 1296 transverter to get started on 23cms. All the advice is to use an IF radio with a max output power of 5W. I would like to use my Icom-7100 with the power turned down to 5W as the IF radio but I understand that some radios can momentarily output more power than set  thus damaging the transverter. Does the group have experience of this combo and/or is there a way for me to detect if the radio does output momentarily in excess of the set power. I have basic test equipment: dummy load, power meter, 50Mhz scope which I suspect will not detect any blip. 


Greg - ZL3IX
 

Damage to the transverter isn't the only problem with using a rig with the ALC working very hard. You need to get someone to check your signal for splatter, or better still use a spectrum analyser if you have one. Making a fast-acting ALC that doesn't cause splatter (spectral regrowth) is not an easy design task and many commercial manufacturers don't succeed in that goal.


Algenon M0JIO
 

This is the circuit I used and the trace is attached below. 


I couldn’t see any overshoot and the height of the waveform corresponds to the 5W of power the radio was set to. My conclusion is that the IC-7100 does not produce excessive ALC Overshoot.