ALC Connection from Icom 735 to AL-811 Amp

[WB2WIK]

An attenuator prevents overdriving the amplifier by the exciter being "driven up against the wall". When I use a peak limiter, it IS impossible to overdrive my "ample-fire" without pushing the exciter to the limit, and I use it all the time.

Get your terms right! It's "apple fryer."

[WA7PRC]

Get your terms right! It's "apple fryer."

If things don't go right, your "apple fryer" produces "ample fire", along the lines of a Neobryllium Reszonifire (a monode device).

[KA9JLM]

Really? I always use ALC with amplifiers that have such provision. With many amp designs, it works perfectly. Maybe not in the AL-811, but then I've never had one of those. I've found the AL-80B and many other amps to work great with every rig I have and always have ALC connected.

I thought we were talking AL-811.

Do you have your 10 dB attenuator Schematic ?

It would be nice to build one that would handle 200 watts or more.

[KO6WB]

We are talking about the AL-811 and how ALC is good or bad. By comparing methods there is an aquired knowledge that can be used to make things work better.
There are amplifier manufacturers that do not include ALC such as Alpha.
An attenuators values are going to depend on the impedance they are working from and into. Usually the first resistor in the circuit takes the most power dissipation. There are programs available on the net to calculate these values for you. Here's one; http://www.microwaves101.com/encyclo...attenuator.cfm.
73
Gary

[WA7PRC]

I thought we were talking AL-811.

Do you have your 10 dB attenuator Schematic ?

It would be nice to build one that would handle 200 watts or more.

Again, an attenuator prevents overdriving the amplifier by the exciter being "driven up against the wall". By that, I mean the exciter is at the point of gain compression (the point at which the output ceases to increase and distortion begins to rise sharply). If you have a hard time maintaining the correct drive level, an audio peak limiter is the better device to use. When a peak limiter is used, it is IMPOSSIBLE to overdrive the amplifier. Broadcast stations use them to prevent overmodulation.

[WB2WIK]

An attenuator will work on all modes including CW, FM and RTTY, though.

Some amps have one built-in. The older Alphas all did. Many solid state amps using FETs do also, as they only need a small amount of power to achieve full output.

I've homebrewed lots of 50 Ohm power attenuators over the years, but nowadays surplus commercial stuff from Bird et al. are so inexpensive at the Swap Meet, it would literally be cheaper to buy one! Last Bird unit I bought was 100W CCS, 50 Ohms, 10 dB, good to 1 GHz and cost $20. It has heatsink fins; I suspect blowing air across the fins would allow 200W operation. These seem to all have N connectors, so some may need to use adapters with them.

[WA7PRC]

An attenuator will work on all modes including CW, FM and RTTY, though.

Some amps have one built-in. The older Alphas all did. Many solid state amps using FETs do also, as they only need a small amount of power to achieve full output.

I've homebrewed lots of 50 Ohm power attenuators over the years, but nowadays surplus commercial stuff from Bird et al. are so inexpensive at the Swap Meet, it would literally be cheaper to buy one! Last Bird unit I bought was 100W CCS, 50 Ohms, 10 dB, good to 1 GHz and cost $20. It has heatsink fins; I suspect blowing air across the fins would allow 200W operation. These seem to all have N connectors, so some may need to use adapters with them.

Again, an attenuator works ONLY by making the exciter work harder, up to the point where it begins to no longer be linear. For AM and SSB, this is a bad thing. For CW, FM, and RTTY, that's not nearly as much of a concern. While it has been typical of hams to run things to the ragged edge, for AM and SSB, I'd rather have overhead in the exciter. Audio peak limiters dirt cheap though cost shouldn't be the most important criteria.

Now, back to 7QP, NEQP, and INQP.

[KA9JLM]

Again, an attenuator works ONLY by making the exciter work harder, up to the point where it begins to no longer be linear. For AM and SSB, this is a bad thing. For CW, FM, and RTTY, that's not nearly as much of a concern. While it has been typical of hams to run things to the ragged edge, for AM and SSB, I'd rather have overhead in the exciter. Audio peak limiters dirt cheap though cost shouldn't be the most important criteria.

Now, back to 7QP, NEQP, and INQP.

If you select the proper attenuator value for the driver I do not see a problem.

Am I missing something ?

Different modes are going to affect the needed amount of drive and duty factor.

[WA7PRC]

If you select the proper attenuator value for the driver I do not see a problem.

Am I missing something ?

Different modes are going to affect the needed amount of drive and duty factor.

Apparently, you're not the only one missing my point. Let's turn it around.

How much attenuation do you think you need? Attenuators that would be suitable for this application are not continuously variable. You would need to design it for just enough attenuation to keep from overdriving the amplifier, with the exciter running at just below the 1 dB compression point. Not enough attenuation, and you can still overdrive the amplifier. Too much, and you can't drive it to its maximum output without undue distortion from the exciter.

That's why I say it's far easier to put an audio limiter between the microphone and transceiver. They're everywhere, and not all that expensive.