HT-44 noise on SSB
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What is the position of your MIC GAIN?
Walt Cates, WD0GOF
?
From: [email protected] <[email protected]> on behalf of Floyd - K8AC <floydsense@...>
Sent: Saturday, May 11, 2024 10:06 AM To: [email protected] <[email protected]> Subject: Re: [HallicraftersRadios] HT-44 noise on SSB ?
No luck with rivet investigation.? I've done a couple of things that have made noticable improvement, but not solved the problem entirely.? I used this method of measurement to observe the effect of changes I've made:? LSB mode, mic gain fully clockwise,
operation switch set to MOX, ground the PTT line at mic jack (no mic connected).? Before any changes, this resulted in an RF output of 12 watts on the external wattmeter (feeding a dummy load).? That's with the carrier null adjusted for minimum carrier level.??
The first change was to replace the original two coax lines running from the mic amplifier stages to the mic gain control on the front panel.? The original lines were tightly laced into the wire harness running along the right edge of the chassis (as seen from bottom with front panel facing you).? The result of this change was a reduction in the RF output from 12 watts to 8 watts.? The new coax runs are separated from the wire harness as much as possible.? Zip tying them together makes the run stiff enough that it stays in place pretty well. After reading about a similar problem in a different make of transmitter, I examined the routing of the AC wiring from the rear panel connector to the on/off switch.? Once again, the AC carrying wires were laced into the large wiring harness that's routed close to the high gain mic stages.? I replaced that arrangement with a new twisted pair running directly from the rear panel connector to the on/off switch.? This time when I tested the output level, it was only 4 watts.?? At this point, I'm wondering what the observed RF output level might be of other HT-44s, with the mic disconnected, but the mic gain turned up all the way.? Other HT-44 owners - please comment on what you see on your transmitter.?? 73, Floyd |
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Ok I re-read your email again.
You are most likely over driving the mic amps.
To properly measure the noise level:
1, Inject a 5mv RMS signal into the mic input.
2, Turn the mic gain to minimum.
3, Key up in ssb.
4, Advance the mic gain until you reach saturation and back off about 5%.
5, Unkey, disconnect the audio, and put a 600ohm resistor from the mic audio input pin to gnd.
7, Key up and make the noise measurement.
Walt Cates, WD0GOF
?
From: [email protected] <[email protected]> on behalf of Floyd - K8AC <floydsense@...>
Sent: Saturday, May 11, 2024 10:06 AM To: [email protected] <[email protected]> Subject: Re: [HallicraftersRadios] HT-44 noise on SSB ?
No luck with rivet investigation.? I've done a couple of things that have made noticable improvement, but not solved the problem entirely.? I used this method of measurement to observe the effect of changes I've made:? LSB mode, mic gain fully clockwise,
operation switch set to MOX, ground the PTT line at mic jack (no mic connected).? Before any changes, this resulted in an RF output of 12 watts on the external wattmeter (feeding a dummy load).? That's with the carrier null adjusted for minimum carrier level.??
The first change was to replace the original two coax lines running from the mic amplifier stages to the mic gain control on the front panel.? The original lines were tightly laced into the wire harness running along the right edge of the chassis (as seen from bottom with front panel facing you).? The result of this change was a reduction in the RF output from 12 watts to 8 watts.? The new coax runs are separated from the wire harness as much as possible.? Zip tying them together makes the run stiff enough that it stays in place pretty well. After reading about a similar problem in a different make of transmitter, I examined the routing of the AC wiring from the rear panel connector to the on/off switch.? Once again, the AC carrying wires were laced into the large wiring harness that's routed close to the high gain mic stages.? I replaced that arrangement with a new twisted pair running directly from the rear panel connector to the on/off switch.? This time when I tested the output level, it was only 4 watts.?? At this point, I'm wondering what the observed RF output level might be of other HT-44s, with the mic disconnected, but the mic gain turned up all the way.? Other HT-44 owners - please comment on what you see on your transmitter.?? 73, Floyd |
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Walt - I will do what you suggest.? Interesting.? But - the noise is there WITH NO AUDIO INPUT AT ALL.? Unplug the mic, key the PTT and turn up the mic gain.? Noise begins at very low mic gain setting.? With mic gain all the way clockwise, the noise is strong enough to produce 4 watts of RF output.
Floyd |
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When you unplug the mic you remove the load from the front end of the mic amp chain. When you turn the mic gain to max all the noise in the unloaded first mic amp is fed to the second mic amp. The normal range for the mic gain is 2-4 for a crystal mic and
3-5 for a dynamic?mic. Amplified mics should not be used on the 44 or any of the SR series.
Walt Cates, WD0GOF
?
From: [email protected] <[email protected]> on behalf of Floyd - K8AC <floydsense@...>
Sent: Saturday, May 11, 2024 1:33 PM To: [email protected] <[email protected]> Subject: Re: [HallicraftersRadios] HT-44 noise on SSB ?
Walt - I will do what you suggest.? Interesting.? But - the noise is there WITH NO AUDIO INPUT AT ALL.? Unplug the mic, key the PTT and turn up the mic gain.? Noise begins at very low mic gain setting.? With mic gain all the way clockwise, the noise is
strong enough to produce 4 watts of RF output.
Floyd |
waltcates
Floyd - K8AC