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eHam Forums => RFI / EMI => Topic started by: VE3TMT on September 09, 2015, 08:12:40 PM



Title: RFI from Astron VS-35M Power Supply
Post by: VE3TMT on September 09, 2015, 08:12:40 PM
Approximately every 60Hz across the HF bands I am getting about S-3 of noise. I disconnected the Astron and ran the radio of a 12V battery. The noise is gone. I read that some Astron models have a connection from the (-) terminal to chassis ground and this can introduce 60Hz hum and interference. Anyone have any experience with this?

Max


Title: RE: RFI from Astron VS-35M Power Supply
Post by: WB4SPT on September 10, 2015, 05:48:27 AM
That's a linear supply with a 5mV spec output.  Do you have an oscilloscope?


Title: RE: RFI from Astron VS-35M Power Supply
Post by: VE3TMT on September 10, 2015, 05:55:46 AM
Sorry, no scope here.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: WB4SPT on September 10, 2015, 06:54:34 AM
In lieu of a scope, AC or RF millivoltmeter;  I'd try a .01 to .1uF cap between - and +.   If not solved, try a direct connection from - to frame. 


Title: RE: RFI from Astron VS-35M Power Supply
Post by: WA2ISE on September 10, 2015, 08:43:31 AM
Small caps (like 0.1uF ceramic) across each rectifier diode may help.  Either the diodes are ringing, producing RF upon each power cycle peak, or external RF is getting modulated by the diodes turning on and off at the 60Hz rate.  The RF signal strength getting varied when the diodes being on vs being off. 


Title: RE: RFI from Astron VS-35M Power Supply
Post by: WB4SPT on September 10, 2015, 10:19:38 AM
Small caps (like 0.1uF ceramic) across each rectifier diode may help.  Either the diodes are ringing, producing RF upon each power cycle peak, or external RF is getting modulated by the diodes turning on and off at the 60Hz rate.  The RF signal strength getting varied when the diodes being on vs being off. 

good input,  If Max is willing to go inside the unit, this is best.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: VE3TMT on September 10, 2015, 10:22:53 AM
No problem,

Ordering parts this afternoon.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: AC7CW on September 10, 2015, 11:52:58 AM
The power supply has to be using full wave rectification of the mains after a stepdown transformer. That should produce noise at 120hz spacing. If something is happening only every other half cycle it's a problem in the diode bridge perhaps. With an O'scope you could sort that out in a minute.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: WB4SPT on September 10, 2015, 02:15:27 PM
I think the premise here is that there is a diode, one of the high power rectifiers, causing RF hash.  In common topographies, only half the diodes are conducting at a time, thus the 60Hz, not 120Hz.  But, I gotta say it's odd for a rectifier system to produce enough energy at HF.  At 14 MHz this is the 233,333 harmonic... Most all of us are using AC to DC supplies without ever seeing this issue.  
Now, I have seen bench top linear supplies oscillate, due to control loop issues.
Maybe Max has a diode with a bad wirebond and its sparking ???


Title: RE: RFI from Astron VS-35M Power Supply
Post by: AA4PB on September 10, 2015, 03:11:20 PM
Reverse biased diodes are often used as RF noise generators although the output is really small and needs to be amplified to be useful. It could be an issue with the diodes so a bypass capacitor may help. You could also bypass the electrolytics with disk caps and/or the +/- output terminals to keep the noise from following the DC power wiring.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: KZ1X on September 11, 2015, 06:01:45 AM
"Approximately every 60Hz across the HF bands I am getting about S-3 of noise."

How are you seeing every 60 Hz?  May I assume you are tuning and watching the S meter?
Or do you have a panadapter?  In what mode are you listening?

"I disconnected the Astron and ran the radio of a 12V battery. "

Terrific technique.

Many of the responders here are making the assumption that the power supply is creating the noise you are experiencing.
I feel a more likely mechanism is that the linear Astron is simply coupling to the radio a noise that's on your AC power line already.
To test this theory, please use a switching type power supply and see what happens.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: VE3TMT on September 11, 2015, 06:06:43 AM
"Approximately every 60Hz across the HF bands I am getting about S-3 of noise."

How are you seeing every 60 Hz?  May I assume you are tuning and watching the S meter?
Or do you have a panadapter?  In what mode are you listening?

Correct, I am using a panadapter display. 14.090, 14.150, 14.210, 14.270, 14.330 etc all the same buzz and viewable on the panadapter. Monitoring on USB.

The Astron is the only supply I have other than the battery so I am unable to test on a switching type power supply.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: AA4PB on September 11, 2015, 06:18:56 AM
Run off battery. Connect a piece of wire into the antenna jack. Move the wire close to electrical power wiring, lamp cords, etc. and see if you detect the same noise. It's a good point that the RFI could be on the power line and coupled through the power supply to the radio.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: AJ4EV on September 11, 2015, 06:25:03 AM
You are seeing the noise every 60 KHZ not 60 HZ

73 de Terry
AJ4EV


Title: RE: RFI from Astron VS-35M Power Supply
Post by: VE3TMT on September 11, 2015, 06:26:15 AM
Yeah, sorry meant every 60 KHZ

I've been reading where 60 Khz RFI is routinely caused by wifi routers, or the cheap DC adapters that power them. I'll check out my wifi system over the weekend.


Title: RE: RFI from Astron VS-35M Power Supply
Post by: N5EG on September 11, 2015, 09:27:44 AM
This doesn't 'smell' at all like a problem with the Astron supply.
Without knowing the details we can speculate that there is 60 KHz-rate
noise on your AC power lines, and using the Astron merely provides an
ingress route for that noise to your radio from the AC power lines.

There's a couple of ways to check this:

1. Turn off all the breakers in your house except the one feeding the Astron
and see if the 60-KHz stuff is still there. If it's gone, you know that something
in your house is injecting it onto your AC power lines.

2. If that doesn't work, the noise source might be on the same breaker as the Astron.
Try using a long extension cord to plug the Astron into a outlet controlled by a
different breaker, and turn off all breakers except that new one.

3. If neither of those work, wrap the AC power cord of the Astron through a ferrite
common mode choke (Mix 31) several turns.  For the duration of this test make sure
there are no sneak paths to ground from your transceiver (which could short out the
ferrite choke), but only the path to ground through the power supply / ferrite choke.

If any of these steps succeed, you know it's not the power supply but something else
on your AC line.  60 KHz is a very common switching power supply frequency, and the
identifiable clump on the panadaptor suggest this.


-- Tom, N5EG





Title: RE: RFI from Astron VS-35M Power Supply
Post by: WA2ISE on September 11, 2015, 09:58:32 AM
I have a Samlex switching power supply that emitted crud every 60Khz or so, found this mod quieted it down: http://www.qsl.net/gm3woj/sec1223mod.htm (http://www.qsl.net/gm3woj/sec1223mod.htm)

But IIRC yours is a linear supply, but maybe the LM723 is misbehaving.