2 Way Radio Site / Switching Devices That Don't Make RFI

mcnutt13579 · May 2017

I work mainly in the off-grid home market but also have 2 way customers.

I know what I like for off-grid homes but RFI is not much of a concern there. I know when I drive near a power supply room/shack my scanner often goes crazy with all the birdies/harmonics thrown by undetermined switch mode devices.

If starting from scratch, how would you build a solar off grid site to minimize RFI? Specifically it seems that the common charge controllers would be suspect to cause RFI unless proven otherwise. I like Midnite but am open to other brands. Frequency range in question is usually 150 MHz but sometimes 46 MHz.

I am thinking for compatibility purposes a -48V battery bank would be nice but do any charge controllers support positive ground?

Then use a Wilmore or other specific 2 way power converter to get +12v for radios and things.

Thoughts?

BB. · May 2017

Look for solar charge controllers (and AC inverters) that are FCC Class B (ideally, Class A is a looser standard for "commercial" devices) rated devices. Many of the cheaper brands/models do not bother with the FCC testing (and frequently can be quite RF noisy). Generally, FCC is measuring 30 MHz and above for radiated noise.

For conducted emissions, the range is 450 kHz to 30 MHz.

If you find devices that have been qualified for immunity testing--That usually also means that the device has less EMI/RF emissions (i.e., if the device is immune to electrical interference, it is also less likely to emit RF energy):

http://www.analog.com/en/analog-dialogue/articles/emc-ce-mark-iec801.html

I would run AC and DC wiring in metal conduit. Any exposed wiring should be run in parallel (or even twisted pair) to reduce "antenna effect"). Do not loop wires (+/-. Hot/Neutral, etc.) to solar array, battery bank and such. In theory, you only need to run the conduit about 10 feet out from the "noisy devices" (solar charge controller, etc.). Beyond 10', RF will not usually leak out of conduit/shielded cables.

You can use "lossie" ferrite chokes (use for RF/EMI control) for wiring to reduce common mode noise. Wrap pairs of +/- DC power cables through chokes (single + or - wire through chokes will saturate the choke core (DC current).

Power electronics and AM radio do not work well together.

https://motherboard.vice.com/en_us/article/why-electric-cars-are-ditching-am-radio

Electric cars may be energy efficient Earth-saving futuremobiles, but their rise could also have a strange unintended consequence: killing off the oldest form of radio.

Two popular electric cars, the BMW i3 and Tesla Model X, are ditching terrestrial AM radio because electromagnetic noise from the electric motor interferes with the broadcast reception, causing static, as the blog Music 3.0 recently pointed out.

Electronics have always been a source of AM radio static, and electric motors are no exception. EVs are powered by a rechargeable battery, electric motor, and a frequency converter that controls how much power the car's electrical motors put out by turning voltage on and off thousands of times a second, basically chopping up energy. This process causes electromagnetic interference that gets picked up by the radio.

You could have a 24 or 48 volt battery bank and use a MPPT type solar charge controller to down convert to a 12 volt battery bank--And avoid some of the RF nose from an AC inverter.

We have a few HAM folks here--Perhaps they can say which equipment they have found to be reasonably quiet.

-Bill

BB. · May 2017

By the way, why do you want a positive grounded battery system? It is common in telecom, but rare elsewhere. Most devices are negative ground and use ground referenced signalling.

There are a few random positive ground solar charge controllers--And you can positive ground a negative ground design charge controller--But you need level converters (or similar) for any signaling between black boxes (and fusing/circuit protections as the 'negative reference' is now "hot").

The usual reason for positive ground otherwise is for cathodic protection and not HAM (or similar) radio systems.

https://www.solar-electric.com/ae15ampsocap.html
http://www.amerescosolar.com/solar-power-cathodic-protection

-Bill

mcnutt13579 · May 2017

The reason for positive ground is just that, for telecom equipment. If we run a 48V battery bank it might as well be -48V if possible for maximum compatibility. I'm not sure how much equipment out there wants -48 and how much doesn't care about ground reference. But it is the standard.

I kind of assumed no AC inverter. I don't see much reason for one. Almost all radio gear can be sourced to run on +12VDC. I would rather not have a 12VDC battery bank though, because radios really want around 14 VDC and if they start to get into the low 12s they begin to lose their mind sometimes. Switch mode supplies 48->12V or 24->12V are readily available through radio distribution channels, though.

Just thinking through options here. Ideally I think I would like a Midnite charge controller. I like them and understand them. Just hoping they are not noisy. Looking for independent confirmation on the subject. I have many in service on off grid houses. But there are a lot of modes that need to be tested. Bulk, absorb, float, idle, day, night, various frequencies. I have learned to assume absolutely nothing when it comes to power electronics and noise.

BB. · May 2017

When I designed some 48 volt telecom equipment... The main (computer) power supplies did not care about grounding. the only thing that "needed" (not really) -48 volts was for E&M signalling--Could use a very small -48 VDC converter for that (unless you are doing a PBX type unit vs voice mail/etc.--PBX needing more power ringing POTS lines).

Depending on how much power you need to move around--I tend to like going with an AC inverter as it is much easier (and safer in some ways) to move 120 VAC 60 Hz around rather than 12-48 VDC (lower voltage, higher current, arc fault issues with DC, AC can use GFI to prevent ground fault shorts/shocks). Of course, one more converter (AC to DC==Losses and possible RF sources) for your telecom and DC powered radios.

-Bill

Estragon · May 2017

@mcnutt13579

You might want to ask about noise on the Midnight forum. I think some of the folks who work at MN are ham ops and will likely be quite fothcoming in if/how their gear interferes and how to mitigate.

mvas · May 2017

Put the charge Controller inside a wire mesh (good air-flow) Faraday Cage - grounded.
Cheap , easy & effective.

If needed, then add a Ferrite Bead / Low Pass filter to all wires emitting RFI that pass through the cage.

http://solarmusings.blogspot.com/

BB. · May 2017

Note that DC chokes (ferrites) do not, typically, handle much current (as in above circuit). (don't remember the details, but typically over a few amps is enough to saturate?).

Generally, just go for common mode chokes. Both + and - leads wound in parallel (same direction) so that the + and - currents cancel each other out.

A common mode choke will reduce "common mode RF noise"--But not differential noise. Generally, common mode noise reduction is a big help.

-Bill

BB. · May 2017

Image result for common mode dc power filter

243 × 300 - palomar-engineers.com

Dave Angelini · May 2017

This is what I see in Telcom because it is from a bankable company that a bank will put money up for operations. It can be changed from positive to negative to floating in the time it takes to remove the from cover.

mcnutt13579 · May 2017

Very little experience with Schneider electric here other than to say when we have tried them, we (or the customers) seemed to wind up sorry. I understand the bankable company bit. They seem a bit unfriendly and the products miss the mark compared to Outback and Midnite who are (or were) friendly.

Dave Angelini · May 2017

Definitely not a DIY company and they do expect the installer to be knowledgeable and to have taken the training. They are just not interested in forums or the teaching of newbies. They do cut the state of the art and have along history back to Trace of building the best or being among the best.

I like Outback also and would never use a company that did not build an entire line of Inverters and all of the rest of the equipment. To sell mixed up equipment makes to hobbyist is one thing, I can't do to the average offgrid homeowner.

They just do not have the skill or time. In my opinion the gear should be easy to use once it is properly installed.

Vic · May 2017

The following Thread ... errrrrrrrrrr, Discussion covers many of the basics, but may be a bit dated about the current state of Emission Certification for some hardware.

http://forum.solar-electric.com/discussion/4685/radio-noise-from-pv-system#latest

With MPPT CCs, the PV leads can be important to try to focus on first ... it does all depend ...

For the HF Comm gadgets here, use 240/120 VAC. For small Comm sited, perhaps using DC as the power source may work OK. Many HF Transceivers really like 13.8 VDC to meet specs (as noted by mcnutt...).

The MidNite Classic is FCC Class B.

Good Luck, Vic

2 Way Radio Site / Switching Devices That Don't Make RFI

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