compiled by William Eric McFadden

Each author retains copyright.

From Brian, KV9X on Jan 29, 1996

Have had alot of fun today finishing my qrp+ mic project. This mic is made from the Radio Shack "PC MOUNT" electret mic, an old shoe, and a dental floss container (empty).

The shoe is used for a chunk of rubber off the sole. The mic is placed in a hole in the rubber chunk. The rubber chunk is glued inside of the floss container.

I cut a slit in the floss container and mounted a switch from the junkbox there. I took the long skinny part from a pen cap and cut it to fit onto the switch to for the part you click with your hand. (I used glue to secure everything). I wired it all to a mic chord and closed the top of the floss container. Cute. As a final touch, I cut the velcro from the old shoe and put the matching (hooks) side onto the shelf above the QRP+. First contact with Floss Mic was Hank, N7GGC, in Kirkland, WA. He said that this mic sounded almost as good as the converted Icom Speaker/Mic I borrowed from my IC 2AT and rewired the week of FD.

From Larry East on 21 Aug 1995

First, some thoughts on the problem of low SSB power output from the QRP-PLUS. I believe there are three issues to address:

1. The effect of the Plus's low microphone input impedance;

2. The effect of the Plus's ALC circuit on SSB output;

3. The problem of trying to measure SSB power output.

The microphone input impedance is determined by the 500 Ohm gain pot and is low enough to "load" HI-Z microphones (crystal, ceramic, etc.) to the point that there may not be enough output to properly drive the rig. The Plus is designed to work with electret mics which can work into a low impedance. Low-Z dynamic mics might also work, but I haven't tried one. To use a hi-Z mic, you might try putting a simple emitter (or drain) follower in the microphone. Using a PNP transistor (or P channel FET), you could probably make use of the "bias" voltage intended for an electret microphone as the power source, with the 4.7K series resistor in the Plus acting as the emitter (or drain) resistor. I haven't tried that either, but if you do and it works, remember where you heard it first!

Now for the ALC; this is intended, as stated in the manual, to insure that the final FET remains in its linear range during SSB operation by limiting the peak output power to a preset value. Unfortunately, the ALC level is not adjustable, and normal component tolerances probably result in SSB output varying by ~10% or more from rig to rig. In my case, using an electret mic, I get about 5W PEP output on some bands, and about 4W on others. Probably a useful mod would be to make the ALC level adjustable and, perhaps, frequency compensated?). Using a 'scope and two-tone oscillator, one could then set it to give the maximum power output commensurate with linear operation.

I would NOT suggest disabling the ALC altogether; not only does it keep you from driving the final too hard, but it also reduces the effects of mic gain, mic position and speech level on the audio output; in a sense, it is a simple speech processor. I saw a post where the comment was made "...there is no ALC on CW, so why have it on SSB?" The answer is that we don't care about linear operation on CW -- remember the days of Class C amplifiers? (Whoops! showing my age...)

I believe that some of the "low output problems" may be due to measuring SSB output on a normal Wattmeter, which essentially measures "average power". Lots of folks expect such meters to indicate the "peak power" in voice peaks, but it don't work that way. For 5W PEP (Peak Envelope Power) output, a "normal" wattmeter will probably show something between 1 and 2W, depending on characteristics of the meter and the speaker's voice. If you have an Oak Hills WM-1 (or similar) Wattmeter, it can be fairly easily modified to indicate PEP; see the December '94 issue of QRPp and January '95 issue of QRP Quarterly for two variations of the mod (the one in the Quarterly is probably the best -- not bragging since I wrote 'em both!).

From Jerry Parker, WA6OWR, on 24 Aug 1997

When I disposed of my Kenwood Twins and replaced them with my QRP+ I found that I needed to hook up a mic so I could make the schedule on SSB.

Well, it was not as easy as I thought. I tried several different electrets. Some from Radio Shack, some I had on hand and some out of cordless phones. Even tried a hand mic from a HT as suggested by the manufacturer.

No matter what I did, my friends always claimed the audio sounded bad, not like myself etc.

I then grabbed my old Sure 444 and hooked it up setting the switching up as with the electrets. I experimented with a DC blocking capacitor in series with the mic lead until the rig sounded good into a dummy load on another receiver.

Next time I checked into my weekend schedule all my friends commented on how nice it was to have me up on my Kenwood Twins again. Of course I brought them up to date.

Here is how I wired the mic:

		mic hot_____33 uf________Tip
		             cap

		   PTT___________________Ring


		Ground___________________Sleeve
	

You should be able to use your favorite old handmic too using this scheme.

From Paul Erickson, VE7CQK, on 24 Aug 97

Just a word of caution on those playing with mic's for their qrp+'s. Make sure any "bad audio" reports you get are due to the mic and not the power supply. I found that in the process of playing with various supplies that they could have profound effects on the ssb quality, and the culpret was rf filtering. I would always test a new mike with a battery first. Then see if there is a difference with the other supply. I use a RS element in the mic case that came with mine, and reports seem fine.

On 2 October, 2004, Michael Pupeza, VE3EQP, wrote that he uses an MFJ-285W; it plugs right into his upgraded QRP+.