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Author Topic: pulse/noise on rs-35m astron on 80m  (Read 742 times)
KB3DRF
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Posts: 11




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« on: October 30, 2001, 06:43:06 PM »

I HAVE PULSE/STATIC NOISE ON 80 160 ON MY RS-35M
ASTRON POWER SUPPLY.THE SUPPLY IS A LITTLE OVER A YEAR OLD.THE NOISE STOPS WITH NOISE BLANKER ON.BUT IT IS A PAIN WITH MY 746ICOM WHEN SIGNALS ARE STRONG I GET DISTORTION(BLANKER ON) IT IS DEFINATELY THE ASTRON.I TRIED ANOTHER RECIEVER WITH NO NOISE,TURN THE SUPPLY ON AND THAT RECIEVER MAKES THE SAME NOISE. GOT A BAD POWER SUPPLY,BUT CAN I FIX IT.IS IT THE CAPACITORS IN THE BRIDGE CIRCUIT? ANY HELP WOULD BE APPRECIATED!
MATT KB3DRF      E-MAIL KB3DRF@ARRL.NET
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WB2WIK
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« Reply #1 on: October 30, 2001, 06:56:21 PM »

Holy cow, that's unusual to have noise from a linear type power supply.  There are no "capacitors in the bridge circuit" in an RS-35M...the capacitors are filter capacitors across the output of the bridge.  I suppose one could be breaking down and internally arc'ing, or something else is, to be making the noise you hear.

I'd probably send it back for warranty repair or replacement, but in lieu of that, it might be kind of fun to open it up, and (carefully!) operate it with the cover off, using a small, insulated probe "antenna" connected to an 80m receiver, to see if I could determine exactly where the noise is coming from.  The probe could be a few turns of insulated wire, twisted and connected back to the receiver RF input jack, or maybe just a nail with some shrink tubing over it to make a "point" probe.  If you try this, whatever you do, make sure it's insulated, since you could accidentally touch live wiring in the power supply.

Using such a probe to "sniff around" inside the power supply might be very revealing.

If you have an oscilloscope, that might be beneficial as you could "see" what's happening inside the power supply as you listen on 80m, to see what kind of event coincides with the noise pulses.

If the noise is more like "hash" (wideband noise that just happens to be stronger on 80m, but has no specific frequency or identifiable repitition rate), possibly the linear regulator in the power supply is unstable and oscillating.  This would be unusual, but according to Murphy, "anything's possible."

73 de Steve WB2WIK/6
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W5HTW
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« Reply #2 on: October 30, 2001, 07:09:17 PM »

Odd.

Safety First.  Think safety, then proceed.  

Make another check.  Disconnect the power supply from everything except the wall socket.  Disconnect any external ground, disconnectthe supply from any radio.  Now, using the other receiver, flip the supply on and see if the noise is there.   If need be, connect a single wire at one end only to the power supply's plus output, but be sure the other end isn't touching anything!  

Also, as still another test, disconnect the antenna from the Icom.  

Then, with the supply connected to the Icom, and the supply ON, and the Icom OFF, check with your other receiver.  Does turning the Icom on or off affect this noise you are hearing?  

Finally, move the power supply and the Icom (you don't need the antenna) to another part of the house, or out to the garage.  For an antenna, just use a 6 inch piece of wire (bare on one end) stuck into the coax jack on the back of the Icom.  

Since you say this is "on 80 meters" I have to wonder why it is not on other bands.  Or is it?  If it is the supply you should hear it on other bands, although possibly at different signal strengths, and that applies to hearing it on the other receiver as well.   Also, if it is the supply, you should be able to hear it with just a tiny wire in the antenna jack on the Icom.   You might also listen on a portable AM radio, especially a battery operated one, by holding it close to the supply, with the supply disconnected.

Several possibilities.  A ground loop springs to mind, allowing picking up something external, such as an engine in the area, or very specifically, power line noise from nearby transformers, poles, HV lines, etc., something that is traveling along the neutral line.  With the supply off, the loop is no longer in effect.  Moving the supply, or disconnecting any ground wire running to it, may point this out.  

If disconnecting any external ground doesn't help, try ADDING a ground.  Ground to the "ground' screw on the power supply and to a good station ground, NOT the ground at the three-prong AC line.  However, I'd use a DVM or VOM and measure the voltage between the power supply chassis and the ground terminal on the AC socket, first, then between the power supply chassis and your intended "station ground."  Don't measure it with your body!!  Don't touch that external ground and the chassis at the same time until you have assured yourself there is no voltage on the power supply chassis.
Not being able to hear the noise, it is difficult to diagnose, but if that is a switching supply, (I don't recall but I think it is) there may be a fault in the switching circuit.   I gave up on switching supplies and switched to standard DC supplies, eliminating those birdies.   My 35 AMP MFJ is absolutely clean and stable, regulated, and has zero birdies as there are no oscillators.  

The description is of power line noise.  If you find it IS in the supply, you will be looking for shorted bypass capacitors, first of all.  

Good luck
Ed W5HTW
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WB2WIK
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« Reply #3 on: October 31, 2001, 10:34:07 AM »

The RS35M is linear, non-switching.  I've owned several of these units, and still have three, and have never experienced any radiated or conducted noise from any of them.

But in re-reading the original question, I just have to ask: Is anything else, other than your 160/80m rig (IC746 or whatever), connected to this power supply???

WB2WIK/6
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WB6BYU
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« Reply #4 on: October 31, 2001, 11:16:47 AM »

Presuming you have followed the preceeding advice and narrowed
it down to the power supply, I can think of two possible sources of
noise:  arcing or oscillation.

Arcing could be due to dust build-up or a bad bypass capacitor
on the AC line, or fried insulation in the transformer.  In this case,
the interference would have a strong 60 Hz or 120 Hz component
synchronized to the line frequency.  (If you have access to an
oscilloscope, put it on the output of your receiver and look at the
noise spectrum.)
 
While you are at it, it wouldn't hurt to unplug the supply and give
it a thorough check-over for loose nuts/bolts/rivets or other
fasteners, particularly those holding ground lugs or otherwise
carrying electrical current.

The other possibility is that your voltage regulator is oscillating.
This can be caused by inadequate bypassing, and can cause a
number of interesting and/or puzzling effects.  Probe the transistors
and/or IC's in the regulator circuit with a scope or AC voltmeter.
In some cases, the frequency and/or amplitude of the oscillation
may be load dependent.
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NB6Z
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« Reply #5 on: October 31, 2001, 04:40:00 PM »

Mat,
This is a "shot in the dark" obviously, but here goes... The RS20 has a "crow bar" circuit built in to protect against over voltage, and I beleive the RS35 must have it also. The circuit senses voltage above 17 are so VDC and will quickly blow the fuse in order to protect your equipment. It is an active circuit and so it is just possible that it is acting up and starting to oscillate and modulate your power supply. If memory serves me, there is a seperate wire attached to the main +12VDC terminal on the inside of the box that you can simply disconnect to defeat this feature. (Hopefully you have the schematic handy...) Please let us know what you find... GL.
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KB3DRF
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« Reply #6 on: October 31, 2001, 05:22:16 PM »

THANK YOU FOR THE ADVICE,IT IS NOT A SWITCHING POWER SUPPLY. I HAVE GROUNDED TO EARTH 15 FOOT 1 INCH COOPPER PIPE ,5 FOOT  GROUNDING STRAP. I DID ALL TESTS TO MAKE SURE IT IS THE POWER SUPPLY. IT STARTS AT .3KILOHERZ  TO 5 MEGA HERZ. ON ANY RECIEVER. THANK YOU FOR THE HELP. I WILL PROBALY JUST GET A NEW ONE.
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KB3DRF
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Posts: 11




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« Reply #7 on: October 31, 2001, 05:26:36 PM »

THANK YOU FOR THE HELP, NO NOTHING ELSE IS  CONNECTED. THE NOISE IS FROM .3M TO 5M HERZ. IT IS GROUNED REAL!!!!!!! GOOD. IT IS DEFINATELY THE SUPPLY. IT IS NOT COMING IN ON THE ANTENNA.
 THANK YOU AGAIN FOR YOUR TIME AND ADVICE 73
MATT KB3DRF    KB3DRF@ARRL.NET
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KB3DRF
Member

Posts: 11




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« Reply #8 on: October 31, 2001, 05:38:12 PM »

THANK YOU FOR THE ADVICE I AM THE ORIGINAL OWNER AND HAVE ALL THE PAPPER WORK. I AM GOING TO DIS CONNECT THE CROW BAR CIRCUIT AND SEE WHAT HAPPENS(GOT TO GET A NEW SCOPE,HI HI)
 I JUST WANT TO SAY THANK YOU TO EVERY ONE WHO
RESPONDED TO MY QUESTION,THIS IS A GREAT SERVICE  TO USE WHEN YOU HAVE A QUESTION.
73 TO ALL,GOD BLESS AMERICA!!!!!!!!!!   KB3DRF
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