Signal at 22.73 MHz?

[Mikebits]

I was trying to track down some source of noise on my very old HP721A power supply. I noticed some RF signals on my DC output around 22 MHz.
Do you know what this frequency is used for. From a frequency alloc chart it say aeronautical. I am surprised aircraft would use such a low freq, does anyone have more info. Here are some scope screen shots:

 

[bountyhunter]

If it's a switcher, it could be ringing from the magnetics when the switch turns off.

 

[Mikebits]

If it's a switcher, it could be ringing from the magnetics when the switch turns off.

The supply is a linear and this signal is clearly an amplitude modulated signal. It is not originating from my equipment.

 

[JimB]

From a frequency alloc chart it say aeronautical. I am surprised aircraft would use such a low freq, does anyone have more info.

Normal aircraft comms is in the VHF range 110 to 135 MHz (ish), but for ocean crossings they use HF when they are out of VHF range.

Cribbed from this document:


We have this list of HF frequencies used for North Atlantic crossings:

However, looking at your scope traces I am not convinced that what you are seeing is Amplitude Modulated voice transmissions.

Also, I nearly forgot, but on HF, aircraft use SSB not AM.

JimB

 

[Mikebits]

I don't think it is voice transmission either as the modulation rate looks to be around ~1-2 Mhz.

I suppose it could be SSB, it would look similar to AM wouldn't it?

 

[JimB]

I suppose it could be SSB, it would look similar to AM wouldn't it?

Yes, except that in the absence of a modulating signal there is no carrier.

I don't think it is voice transmission either as the modulation rate looks to be around ~1-2 Mhz.

That is what I thought looking at your screen shots.

Do you see this signal with just a piece of wire connected to the scope?

JimB

 

[MikeMl]

Hearing a harmonic of a switcher on 22.730MHz. Most audible as a buzz when using AM detection. It is so incoherent that CW,USB or LSB just cause an increase in the background noise.

The HF propagation has been bad recently, so not hearing any DX above ~17m (18.1MHz).

Likely local in your area..., and I doubt you are hearing the same signal I am....

 

[bountyhunter]

The supply is a linear and this signal is clearly an amplitude modulated signal. It is not originating from my equipment.

Your statement said:

"I was trying to track down some source of noise on my very old HP721A power supply."

Which sounded like you thought it was coming from the power supply.

In my career, I have seen many signals like that and the first thing I do is turn off the power to my circuits.... if the "noise" is still there, it's pickup from external sources.

The output of a power supply has a fairly high impedance to signals in that frequency range so it is possible that the signal is being picked up by external leads.

 

[Mikebits]

Your statement said:

"I was trying to track down some source of noise on my very old HP721A power supply."

Which sounded like you thought it was coming from the power supply.

In my career, I have seen many signals like that and the first thing I do is turn off the power to my circuits.... if the "noise" is still there, it's pickup from external sources.

The output of a power supply has a fairly high impedance to signals in that frequency range so it is possible that the signal is being picked up by external leads.

Sorry I guess I worded things a bit off. The noise I was tracking down was of a different nature, and I just happened upon the 22MHz signal. It is not present all the time. It comes and goes.

 

[Mikebits]

Hearing a harmonic of a switcher on 22.730MHz. Most audible as a buzz when using AM detection. It is so incoherent that CW,USB or LSB just cause an increase in the background noise.

The HF propagation has been bad recently, so not hearing any DX above ~17m (18.1MHz).

Likely local in your area..., and I doubt you are hearing the same signal I am....

I wish I had one of the SDR dongles right about now. I been toying with getting one just for giggles.

 

[MikeMl]

I have a re-purposed TV dongle, an RFSpace SDR-iq, and an Airspy SDR receivers. I am using SDR# and SpectraVue with all three. There are reviews of all three at eHam.com

If I was buying one today, I would likely get one of these.

 

[Mikebits]

Thanks Mike, the specs on that one are impressive. 12 bit AtoD, 5th order filter, and the BW is amazing. Boy things sure have changed since I got into this business. Kinda makes me feel old