I have an FT-101E that's been recapped, aligned, and has a strong set of tubes that have been neutralized and put out full output on all bands. Everything is operational except for a pronounced hum on transmit. I was hoping for some insight on how I should proceed in tracking down the source or likely culprits. Any troubleshooting approach would be greatly appreciated! It is still present if the mic is unplugged and the mox is keyed on the front of the radio. All of the boards were pulled and reseated with no change. Thank you in advance!
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Ft-101e transmit hum
- Thread starter Champo
- Start date
Unfortunately I'm not sure if it's 60 or 120 hz but mic gain had no affect on strength, prevalence or pitch. I don't believe the carrier affected it either but I'll need to confirm that with someone on air. I have a video that was taken on air by someone for me but it won't allow me to attach it. I have a scope available so if you have a location to test in order to confirm I can do that. Thanks.
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If you have a radio that receives FM on hand, tune it to the frequency where the Yaesu transmits and see if the hum is louder when FM is selected than it is when receiving AM.
This would point to the VFO and/or crystal oscillators if the hum is really FM. And if it's louder on AM, this is not the culprit.
73
This would point to the VFO and/or crystal oscillators if the hum is really FM. And if it's louder on AM, this is not the culprit.
73
I can definitely do that. I have an FT-891 sitting next to it. I'll report back.
If it's on FM it is faint or non existent. It seems to be more pronounced on AM. The general description consensus is that it sounds like I have a fan running in the background or buzzing while transmitting. I know it's not a result of the mic picking up background noise though because it occurs if no mic is plugged in at all. There is the factory cooling fan installed on the radio so I'm not sure if that's bleeding in somewhere or if it's completely unrelated. It is also worse on the stock Yaesu hand mic than it is on the Silver Eagle D104 or with no mic. I'm not sure why that is.
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Does the mike gain knob eliminate the hum altogether turned all the way down?
Didn't think to ask. If not, this points downstream from the mike gain control.
73
Didn't think to ask. If not, this points downstream from the mike gain control.
73
Killing the mic gain kills the hum from what I recall. I didn't do that last night when I checked but I'm pretty sure that was the result when I was checking on air with help from another. I probably should have mentioned that. I'll reconfirm but I'm confident this is the case.
I think I've isolated the problem to the external fan on the heat pump unit....or it's at least 1 potential cause. The radio ran fine for several hours tonight. It then experienced the hum during transmit. It seemed to coincide with the external heat pump kicking on. I'll need to explore this more. It was only momentarily though (60 seconds) tonight and then it was gone. It wasn't for a prolonged period of time like the other night. I also didn't pay much attention to external causes the other night since it did it from the get go. Nonetheless it was clearly heard during the conversation I was having tonight. I'm not sure if it's the only cause or one of many that the radios susceptible to. Presuming that it is indeed external, and not some intermittent internal issue, is it likely interference coming in on the AC line or external RF? If it is the AC line would a ferrite bead be of any help or something like the Isobar Tripp Lite to isolate the radio enough to potentially reduce it? Any and all solutions would be greatly appreciated.
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Hmm. Don't quite know what a heat pump could do to the AC power feeding the radio, but what other link between them is there?
The only connection that comes to mind would be to the power factor. Assuming the heat pump uses DC motors, it will have large rectifier bridge circuits being fed straight from the AC line. This tends to distort the current draw on that circuit, adding harmonic frequencies to the line.
Industrial equipment like that is supposed to have "PFC", or power factor correction circuits to reduce this distortion. Don't know about the Heat pump in that department, either. For that matter, I don't know what kind of unintentional trouble it can cause for other devices on the same AC service.
Definitely the first time hearing of this connection.
73
The only connection that comes to mind would be to the power factor. Assuming the heat pump uses DC motors, it will have large rectifier bridge circuits being fed straight from the AC line. This tends to distort the current draw on that circuit, adding harmonic frequencies to the line.
Industrial equipment like that is supposed to have "PFC", or power factor correction circuits to reduce this distortion. Don't know about the Heat pump in that department, either. For that matter, I don't know what kind of unintentional trouble it can cause for other devices on the same AC service.
Definitely the first time hearing of this connection.
73
It could still be simple coincidence. Why I experienced no issue last night except for that momentary interference as opposed to the other night when it was prolonged I don't know. I'm not going to rule the radio out as the cause yet but it looks more likely to be external to the radio. Far from a guarantee though. Unfortunately without it doing it it makes it difficult to troubleshoot. I'll need to wait until it occurs again and then see if anything, heat pump or other, is running at the time. If something is I'll kill it and see if it corrects it. If not I'll try the FM test. Another suggestion I received was to connect my scope up to a nearby radio to see what it is receiving on the scope when the FT-101E is transmitting to see if it's 60Hz vs 120Hz. If this second strategy isn't worth while please let me know. I appreciate all of the help.