Help with HF RFI

[Vic]

Hi boB,

If you are referring to the   tick  tick  tick  tice,   several times per second,  that is  the Classic itself.   We DO hear that here,  but it is much subdued,  compared to the signal level @ Justin's.

Due to voltage drop in the battery cable,  which was made longer by making 3 - 4 turns through some Mix 31 cores,  long ago,  replaced that cable with a short,  direct one with no cores.   Made a little difference in the V drop.   And the 75 M birdies now sing a bit louder   ...   but it is OK.

Will be trying to move one Classic here,  to be about four feet closer to the Classic battery breaker,   and  add a few turns of #2 Ga cable through a monster mix 31 core,  to try to get lowest V drop,  and some more suppression   ...   

73,   CU boB,   GL Justin

[justinbowser]

I have to finish up my battery cabinet before leaving back to the big city this weekend so won't be able to try any of these other tips until I get back.  Before leaving, however, if I get some time I may remove the monster toroid from the in/out wires to the Classic and use this to wrap 10-12 turns of coax through it for a common mode-choke right before the radio.

[justinbowser]

After a trip back to civilization and considerable amount of procrastination I finally moved the Samlex inverter into the battery enclosure and ran the AC wires to the breaker pane through rigid steel conduit.  I also wrapped the hot and neutral wires three turns through an oval shaped mix 43 core right after exiting the conduit.  On 40M the background noise dropped from +20 to S9 and on 20M is pretty much quiet!  I then ran my coax (right before radio) through a mix 31 toroid about 12 wraps in hopes of choking down some of the Classic noise but struck out on that account.  It's looking like I might have to live with the 25 KHz interval "howl" coming from the CC whiole operting in the cabin.  On a brighter note I have finally hooked up the 9 "old" Renogy 100 W panels to the barn through our original 40 A MPPT CC, AGM batteries, and inverter so will try moving the radio out there to see what the change will be.

[boB]

+20 to S9 is certainly better.   I have to live with S8 S9 ALL the time with NO relief from my neighborhood noise.  We had an outage recently when there was a large fire nearby.  The background noise was S ZERO !  (12V battery)  After the power came back on and the noise came back up, I turned off the power to my house.  Still S8-S9 so it isn't me.
This is 40 meters also.  20 meters is better and 80 meters is totally unusable for me except in the mobile now.

An interesting fact about multiple wraps of wire on the toroids is that too many turns can start giving you more noise because of the capacitance from the start to finish of the turns of wire so keep that in mind.

You can also add common mode capacitors to help the noise.  This would be small capacitors from negative and positive to ground on say, the external world side of the toroid.

Can also add caps to the Classic side.  Ideally, two toroids in seires with one differential cap between plus and minus and two caps from minus and plus to ground should give an extra drop in noise, hopefully.

Not easy stuff unfortunately !

[justinbowser]

Bob - Your location sounds like mine in Texas.  I have a power line running about 10' behind my shop which is where my radio is at.  The noise is pretty miserable...

Instead of winding the CC output wires around a toroid coil, and possibly introducing capacitance, would running the + and - lines straight through a few of the "oval" shaped cores do anything?  When I wound the output wires three turns through the toroid it didn't seem to make any difference.

[boB]

Yes, running the wires through a ferrite tube will work also.

If running those wires around the toroid a few times is not doing ANYTHING then the problem may not be what we are thinking.

Maybe there is a differential signal somehow allowing the interfering ?

How about the battery temp sensor wire ?   Or the Ethernet cable ?   Could the issue be those ?

Have you tried removing the Classic from the metal backplate if it is on one ?

Might try those things.  If there are only the 4 wires coming into the wiring compartment (battery and PV) then it's gotta be coming through those except for the chassis iteslf.

[justinbowser]

Bob - Right now the only wires going into the CC are WB Jr wire, PV in, and the output to the battery bank.  The Classic SL did not come with a battery temp sensor so that has never been hooked up.  I had a cable attached to the serial port for monitoring the CC but I have removed that as well.  CC is mounted to the interior OSB wall in the cabin.  If you can tell me what value caps to scrounge and where to put 'em I'll give that a try.  Would it be like an .oo1 uf ceramic cap from each DC cable to earth ground?

Thanks for the help.

[boB]

Yes !  0.001 uF  is perfect !

Might put a small ferrite on the WB Jr. purple wire next to the Classic as well if possible. 

[justinbowser]

Will do that tomorrow.

[justinbowser]

Bob,

I put the WB Jr. wire three wraps around a clip-on ferrite with no change.  So, I got really drastic and moved the radio out to the barn which is about 50' from the cabin and the Classic noise is just as bad as it was inside the cabin.  The barn runs on it's own system, batteries, panels, CC, inverter, etc.  I then shut off the breakers in the MN Combiner box and the noise went away so I am pretty sure that this interference is radiated.  I have not tried the caps yet but will order some.

[boB]

OK, so it sounds like the interference is coming from the solar panel array.

Might try some differential filtering.   I will have to look into that.

Are your PV wires from Classic to the PV array either twisted, close together or in conduit ?

boB

[justinbowser]

My array is 3x3 with each string running into the combiner box with 10 Ga stranded.  8 ga stranded goes from the combiner box underground through 3/4" (I think) PVC conduit into the cabin where it goes up the wall into the CC.  Wires were straight pulled through conduit with no twists.

I currently have no ground on the panels.

As an aside the system that powers my barn is a cheapo Chinese inverter, Chinese CC, etc.  It is quiet as a mouse!  Very discouraging...

[justinbowser]

Bob - My capacitors got here today and wanted to double-check placement.  I will remove the MNGP from the CC and attach one .001 uf cap between all 4 wires and ground, 4 capacitors total correct?

[EequalsIR]

Wow!  Glad to find that others are grappling with this issue!  To date my solution has been to turn off the breaker to the solar panels, turn off the inverter (the PWR for my rig is a dedicated battery bank), and turn off any other circuit causing RFI.  Of course, the Classic is the biggest offender.  This is a pretty radical solution, but it works.

When I'm operating I'm typically doing weak signal work such as SOTA chasing and can't tolerate any RFI.  Sometimes the Classic's birdies are far enough away from my operating frequency to allow me to leave the Classic on, but I usually don't want to risk it.

I haven't finalized my Classic installation yet and am planning to experiment with Amidon's Ferrite Toroidal Cores.  To start with, I'm planning to try 75 Material (suppresses 200 kHz - 30 MHz) beads and #43 beads (suppresses 25 MHz to 300 MHz).  Instead of doing several turns (because of capacitance issues), I'll try to get beads that just fit over the wire and run as many of the longest beads they have (1.25") as I can, possibly through the conduit if I have to.  I'm hoping to avoid using caps as that can get messy and takes up space, especially for 4ga wire.

Of course, different cap values suppress different ranges of frequency; capacitors are self-resonant at a certain frequency.  For thorough bypassing, often different cap values are used in parallel.  10µF would attenuate audio frequencies,  0.1, 0.01 and 0.001µF higher frequencies.  My 1986 ARRL Handbook has a chapter entitled "Radio Design Technique and Language" that covers bypassing and RF leakage well.  If desperate enough, you can alternate between a bead and caps, in series until you've killed all the RFI (and then put the Classic and all this filtering in a Faraday cage -- help!  ).  Sounds like work.

(I'm adding more here:)  Probably the most robust way of suppressing the RF coming from the Classic:

• Enclose the Classic in an RF-tight enclosure
  
• Provide adequate venting and airflow
• Bypass each cable exiting the enclosure appropriately for the signal with ferrite beads and/or caps using chassis-mounted feed-through caps where possible.
• For the connections from the solar panels and battery, create a series of RF-tight sub-enclosures attached to the Classic enclosure with feed-through caps between them.
• In each enclosure, run the line through a ferrite bead or two and bypass with caps.
• Keep adding these sub-enclosures in series until the RFI is adequately suppressed.
• Finally exit these lines through chassis-mount feed-through caps.
• You'll have to anticipate having limited access to the controls and display. Perhaps you could provide a RF-tight door for this area of the classic.  Remote control would make this easier.

In the past, the ARRL Handbook provided great construction techniques for this type of project; the current ones probably do as well.

It would be nice if Midnite or a third-party could create an enclosure like this (or a limited-emissions version of the Classic) for RF-sensitive environments.  The problem is the limited market.  It would certainly worth the money.

73 everyone!
E=IR

[mike90045]

The metal honeycomb air filters are going to be pricey.   You might be able to heat sink the classic to the metal case and use the case as part of the heat sink.  How often do your fans run ?


https://www.pcmag.com/how-to/how-to-make-your-own-faraday-cage
https://mdcreekmore.com/make-a-faraday-cage/