Help with HF RFI

[EequalsIR]

Hi Mike,

You're right.  A Faraday cage is overkill for HF RFI.  The wavelengths for HF are just too long, the shortest being 10 meters.  Even 2m probably wouldn't be a problem, if you made the whole enclosure with perforated metal, like is used with tube transmitters.  Maybe something like https://media.digikey.com/pdf/Data%20Sheets/LMB%20Heeger%20PDFs/PERF-135.pdf.  I haven't checked around much yet as I was going to try stringing beads first.

E=IR

[Vic]

Eequals,

The Ckassic's metal case is an effective  shield  for Radiated  emissions.

In general,  the largest emissions in the HF  frequency range,  are conducted (and then Radiated) on the cables that connect to  the  Classic.

Common-Mode chokes are usually the best bang for the  buck/effort.  Depending on your  frequencies of  interest,  choosing snap-on or toroidal cores,  often,   Mix  31 for good  coverage in the  HF range,  is a  good place  to start.   Place these chokes on all cables that are connected to the Classic,  or other MPPT CCs.  Generally   multiple turns of each cable  through the cores will improve the attenuation,    to  a  point.    Three,  four or,  even  five turns is worth trying.   For toroids,   if possible one can try to spread these multiple turns of cable around the core.  Bi,  or Trifilar  windings of multiple cables  is  best (IMO).

It seems,  that the cables connecting to  the PVs have the largest emissions,   so choking those first is a  good place to  start.

Metallic conduit (EMT is  usually fine0,  containing all of  the cables connected to the Classic,   but  separate conduit runs for the PVs,  battery,  and even  control (BTS, Aux, etc) separate from the  former  two.

Our power room is a Faraday shield  --  a seagoing Cargo Container  --  but this has little effect on the emissions that are  Conducted,   and then,   Radiated,  when they exit the container.   FCC Part 15,  Class B emissions tests for Line Conducted emissions,  begin at  30.00 MHz,   so the entire LF,   MF,  and HF frequencies are not measured,   and therefore,   usually NOT suppressed in devices,  like CCs,  which are not connected to  the AC Mains.

Place the CM  chokes as close  to the  emission  source (the Classic,  in this case),   as possible,   ideally in a metal box,  with continuous EMT grounds,  connecting the box and the EMT for the input,  and output).   Am getting a bit  redundant,   have mentioned this quite  a few times before.

Try to separate the antennas from the PVs,  and power electronics,  as far as possible   ...    and so on,  and on ...   Distribute AC power underground,  and use metal conduit,  where these cables exit  the ground,  etc.

Inverters,   of course,  can have their own emissions.

FWIW,  73  GL,   Vic

[EequalsIR]

Thanks Vic,

Yes, I've been reviewing Tobit's thread regarding his Kid as well as this thread.  Also K9YC's RFI article is very helpful.  Just turning off the PV breaker seems the easy way out.    Like Tobit I also use a 7300 with the same results, but I'm also getting the same signals on other radios, shortwave and 2M, all powered by internal batteries.  I've found your posts to be very helpful.

The problem with SOTA is that most activators are on mountains when the sun in shining. 

E=IR

[boB]

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?

Yes

TO ground.  Chassis  which should be grounded.

[EequalsIR]

Hi Vic,

The Ckassic's metal case is an effective  shield  for Radiated  emissions.

There are four 1 3/8" holes at the bottom of the Classic; there is also the display.  If I were designing an effective RF shield, I wouldn't include holes of this size. (BTW, does the screen metal in the included screen/plugs for these holes go all the way through the rubber or plastic to touch the chassis to effectively create a shield?  I don't have one in front of me.)  Regarding the display:  is there a ground plane in one of the layers of the PC board behind the display that would effectively function as an RF shield?

Perhaps you meant that the RF being transmitted off the antenna power leads is so strong that the RF coming from the case is inconsequential.

I didn't realize that FCC Part 15,  Class B emissions tests for Line Conducted emissions starts outside the HF band.  Gracious!

E=IR

[EequalsIR]

Hi boB,

I hear you're on the design team!  I miss those days.  Regarding the caps, what is the maximum capacitance that the input and output lines can handle?  What about going as high as 0.01 or even 0.1µF (I'm not really referring to bypassing, but rather the stability of the internal circuitry)?

73,
E=IR

[Vic]

Hi Eequals..,

Just my opinion:
Shielding of the Classic,  to the first order of things,  might  help reduce Radiated  Emissions.    One  would expect,   that,  essentially all of the emissions in the HF (and lower frequencies),  are  line Conducted.   Meaning,  that your first efforts would be toward choking,  and  perhaps  LC filtering of the DC cables connecting to the Classic.

Shielding and individual capacitors,  might be expected to have some effect on very high HF frequencies,  and above.

The Classic's case is probably a fairly good shield for Radiated emissions.   It could be made a bit better (finger-stock,  or grounding fingers,  etc),   but why not try chokes on the DC leads first,   metal conduit,  moving antennas,  et cetera,  if your   primary interests are in the HF range?

EDIT, to add:  In fairness to the FCC  and Part 15,  for unintentional radiators,  it is stated,  somewhere,  that these devices "shall not (or similar wording)  cause  Harmful Interference".   This can be  an ambiguous situation, and could even require a  Court to make  that  determination.

AND,  also   should say,  that I expect that  MidNite Solar complies with  Part  15 (as I  understand it),   as there is no prescribed method  and interface to measure Conducted emissions, below 30.00 MHz,   and no Limits specified (as far  as   I know)<.

FWIW,   IMO,  and so on,      73,  Vic

[EequalsIR]

Very good, Vic.  I'm definitely not starting with a box and feed-through caps!  My first approach has been the off switch. 

boB,

I've been thinking about the implications of running the bypass caps to earth ground.  The idea behind the UL's requirements is that no current normally flows on the earth-ground conductor, which is what GFCI detects.  Would bypassing affect the Classic's GFCI functionality?  What's the current threshold? I guess I could look that up.

Bypassing to ground is common with RF equipment.  Depending on the length of the ground wire or strap to the ground rod assembly, certain wavelengths will present an infinite impedance at the equipment being bypassed.  With broad-spectrum emissions like this, certainly some wavelengths will not be suppressed.  The MFJ-931 Artificial Ground comes to mind, but that only addresses a narrow range at a time (depending on the Q). Of course, you could use a wide strap for your ground to lower the Q, but that would involve some effort with a typical structure.  You'd have to be aware of the single point ground requirement to avoid ground loops.

I have more questions, but they'll have to wait.  Isn't RF fun?

Cheers and 73!
E=IR

[boB]

There shouldn't be any limit to the size of cap you could use there but anything large wouldn't help at RF frequencies I don't think.  So no need for big C.

For charge controllers there is no FCC line test below 30 MHz.  This is because it does not connect to the AC line.

But you and I know that below 30MHz is really more important !  I still want to keep things good but it is difficult.

Will help the best as I can !

Where/when did you do design work ?

73

[justinbowser]

Bob - I have not had time to add the caps to the CC, busy winterizing cabin's water systems and back and forth between TX and OK.  Any further messing around on my part will probably not happen until spring.  On my last trip up there (last week) I took an old "antique" 30 MHz scope up and left it so I will try to use that to poke around on stuff to see what I can see.

With the CC interference being just as loud after moving the rig to the "barn" I'm pretty sure the RFI is being radiated from the actual panels.  The fact that my level of interference increased dramatically after switching from the MFJ-2240 portable dipole to the dual band inverted Vee.  The MFJ was in effect 30' completely away from the panels while the inverted Vee (although higher at the apex) has ends that are closer to the panels.  Relocating the antenna would be a last resort for me but may come to that.

I thought it was going to be so nice to have an almost non-existent noise floor being off-grid out in the middle of nowhere!   

[justinbowser]

Oh, Eequals, welcome to the thread - as they say, "misery loves company!"  I was starting to think I was the only one having grief with this!

[ClassicCrazy]

I found that the HF full wave loop antenna I put up cut down on the received noise from my inverter. It is fed with ladder line to 1 to 1 and 4 to 1 baluns to coax into hamshack.

Larry

[justinbowser]

I'm going back up to the cabin in a couple of weeks to take care of a few more winterizing things.  I think I'm going to look for a place to relocate my antenna to to get it further from the array and maybe have a chance to put the scope on the DC lines at the CC and at the combiner box.

[justinbowser]

Made it up to the cabin and had time to put a scope on the DC Output lines.  The attached CC Out pos scope traces are on the +24V line going to the battery bank and the PV IN Pos trace is the pos line in from the PV array.  Things are a bit overcast today so the Classic is not working very hard.  A lot of ringing going on and this same pattern is on the PV input lines as well.  Horizontal scale 5 usec/div and vertical set to AC at .1 V w/ 10:1 probe which makes the noise right at 4V peak to peak on the CC + out and about 5 V on the PV + in.

I forgot my .01 uf capacitors so I will have to wait until next trip to try them out on both PV IN and OUT lines.  I suppose that having 5V of noise on the array could be my RFI problem?

[justinbowser]

Here is the PV in trace...