On the bench:
2012-Jan-05 - Poor Audio
I have been receiving some poor audio reports from the homebrew radio. Sometimes people say it sounds a bit muffled, sometimes they tell me it sounds like RF on the signal. It's hard to test. The radio sounds fine when I monitor it across the room on another receiver. It also looks fine in a classic two tone test.
There are a few possibilities:
- It's possible that it only happens when I over drive it (shouting my callsign into the microphone in the heat of a pileup for example). I can test that using a seperate receiver and perhaps by monitoring the transmitted audio
- It could be filtering of the audio caused by the RF filter that I have on the mic input. I have a 1mH choke and a 0.01uF capacitor. That seems unlikely though, but its easy to test.
- Maybe the inexpensive fist mic produces poor audio or is damaged in some way. I can try antother microphone to test that.
- Perhaps its an issue with the amplifier and not with the radio.
So I intend to find out. I don't want a poor signal on the air.
Enter Comments Here:
Comments on this post
| On: 04/22/12 7:07 BillH@testequip.com said: |
| I had the same problem with my EB104/\"kit\" The mic gain on the amp is critical.
To set up the audio try this:
Using an oscilloscope probe or with a wire lead, lay the wire near the amp and
set the variable display on the scope to a full display with a CW key down. Then
using your mic on SSB observe the waveform when transmitting normally. Reduce
the mic gain until the waveform is not flattopping. My EB104 was flattopping at
above 30% of the range of the mic gain setting.
I have been having trouble blowing out transistors also, so my amp is on hold
till I get some circuits to control finished I also built the control board in
the ARRL Handbook for the SS amp, Using the PCB they used, and also trying some
other methods. I still need to build a power sensor. I am using water cooling
for the amp.
Bill Hedrick |
