I run a pad between a modern transceiver and a transverter. There are two issues with this approach when applied to a Linear. 1) The excess drive power you have to dissipate as heat is considerable so you have to plan for it. 2) The loss of the pad adds directly to the receiver noise figure unless you use a separate receive antenna at the transceiver end.
I recommend that you try one of the other approaches or else go for a modest pad (say 3dB) which may not be enough given your sensitive amp. Dennis AE6C On Wed, Oct 1, 2008 at 5:06 AM, Garey Barrell <[EMAIL PROTECTED]> wrote: > John - > > There are a few ways to do this. I'm not familiar with the Acom unit, but > apparently it doesn't require much drive. > > 1. Construct a "power pad" to put between the TR-7A and the amp input. > This is probably the "best" way from a distortion standpoint, but > inconvenient unless you use the amp all the time. Running any SSB > transmitter with very low Mic Gain is not a good idea, since the S/N ratio > of the AF stages is at its' worst. > > 2. Construct a small power supply to feed a "fake" ALC signal to the ALC > input on the TR-7A and crank the voltage up to where you can run the TR-7A > Mic Gain at 10-11 O'clock and not overdrive the amp. When you want full > output from the TR-7A, just turn off the ALC voltage. > > 3. Construct your own ALC circuit in the amp using the method in the L-7 or > some other amp with similar circuit topology. > > 4. You "may" be able to turn the internal ALC pot on the TR-7A to limit > it's maximum output to a level that won't overdrive the amp. Again, no > convenient way to enable full power for stand-alone operation. > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs > <www.k4oah.com> > > > > John Stringer wrote: >> >> Way back in the 80's I used a TR7 with an L7 which ,of course, had ALC. >> Everything worked well together. >> Now, about 27 years later I have bought a nice TR7A and am trying to use >> it >> with my modern Acom 1000 linear which has no ALC provision. >> There is one problem as a result. I have to turn the drive-meaning >> microphone gain- down VERY low so the TR7 is operating long before it's >> own >> ALC kicks in. As a result there are considerable output swings to the >> linear >> which often causes it to kick out. Turning down microphone gain even >> further >> helps but then the average output is very low. >> I need to be able to operate the TR7 so it's ALC is working whilst giving >> a >> LOT lower drive. >> Any suggestions? John. GI3KDR. >> >> > > _______________________________________________ > Drakelist mailing list > [email protected] > http://mailman.zerobeat.net/mailman/listinfo/drakelist > _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
