RF in PSU

[XXL]

Can’t stop Rf getting into the switch mode power supply’s from eBay. Iv even tried a meanwell one and still doing the same thing. Starts buzzing and puts out limited current. Iv got a ferrite on the positive line coming from the psu. Is there anything else I can do ?

[LeeCavanagh]

It could be rf coming back down your coax if you are not using a balun, what power you running out your PA?

[XXL]

Im using a balun but I think it’s slightly off. It was for a different frequency around 99. Was getting 4w back at 150w

[LeeCavanagh]

I have re read your message , and the fact the power supply itself starts buzzing and you don’t get the correct volts out sounds like you have an under rated supply

150w shouldn’t really cause big issues , besides a balun if it was shear rf overload causing your buzz you could try an emi filter inline the 240v

What exciter are you using ??
What spec is your supply ?
What power does the 150w require?

[XXL]

Ok basically, it’s one of these from eBay.
https://www.ebay.co.uk/itm/165836880625

And the power supply is 600w 24v

[LeeCavanagh]

Hmm, what you described sure sounds like the psu is not rated to the recommended spec
“ Recommend 24V 15A power supply”

Some eBay sellers are a bit liberal with their ratings ,

Difficult to say what your issue is without being there, but you could use a multi meter to see what amps it’s drawing from the unit. Those psu usually have a fan in them, is that coming on? And is the buzz definitely the unit and not a hum on your transmitted signal (your post could be taken a couple of ways).

You mentioned you also had a mean well, you could out both together to double your max amps (if you wanted to try)

[rigmo]

Can’t stop Rf getting into the switch mode power supply’s from eBay. Iv even tried a meanwell one and still doing the same thing. Starts buzzing and puts out limited current. Iv got a ferrite on the positive line coming from the psu. Is there anything else I can do ?

These power supplies do not support the declared loads. always buy a power supply with at least 30% to 40% more power than needed. if even then you have problems with RF, you need to upgrade the filtration inside the device or install an external one at the input. every further consumer on the stake itself has additional filtering LC filters...

[rigmo]

Ok basically, it’s one of these from eBay.
https://www.ebay.co.uk/itm/165836880625

And the power supply is 600w 24v

it is certainly a low efficiency system, let's count about 65% of the entire system.
if we take everything into account, you need a 360-400W power supply

[XXL]

That’s what I don’t get. I’m using a 600w supply

[LeeCavanagh]

I have used this brand and like them
TT Electronics PDF-800-24 Enclosed Power Supply 24V DC 33A 792W

[Albert H]

Bitter experience with cheap Chinese SMPSUs tells me that they're always a false economy! Most of them are designed to drive low voltage LED lighting, and as such are not expecting to be in an environment with lots of RF floating about. RF gets into everything - particularly when it's unexpected - the inputs to the regulator and control ICs are never RF-filtered, and those chips are usually very susceptible to upset by high RF levels. For example: a voltage-sensing input can "see" the DC it's meant to be measuring plus a contribution by the RF that gets rectified inside the IC, and gives the control network inside the IC completely false information.....

I've had those "cheap" supplies just shut down completely when there's RF around, or their output voltage becomes effectively unregulated, leading to the destruction of expensive semiconductors due to over-voltage....

There's a further, more subtle problem with SMPSUs used in transmitters - these PSUs usually work by rectifying the mains then chopping the resultant DC voltage with a crude transistor oscillator to feed pulses at a couple of hundred kilohertz to a physically small, lightweight, high frequency transformer.... The output of the PSU will ALWAYS have some amount of switching ripple on it, and unless the constructor is very careful to filter off the HF ripple, it will end up mixing with the RF carrier, producing spurs at the switching frequency either side of the carrier. Worse, there will be a series of spurs either side of the carrier at multiples of the switching frequency....

Broadcast Warehouse always had problems of this sort with their single-box, at-frequency excited, higher power transmitters. Their >100W, boxes were all rejected by the FCC for approval because the the SMPSU artefacts they spewed. Those rigs were so dirty that BW didn't even try to get any European approvals at first, until they identified an SMPSU that didn't freak out with RF around..... The power supplies they used were most certainly NOT "LED Lighting Supplies"! Also, their "at-frequency" rigs ALWAYS hummed because of RF feedback - on their later versions the hum was reduced, but it was always there!

Most high quality rigs (like most of mine) use the conventional transformer, bridge rectifier, smoothing and analogue regulation approach. Often the PSU is much bigger and heavier than the rig itself, but you can be absolutely sure that there won't be any nasty surprises!

[radium98]

Most high quality rigs (like most of mine) use the conventional transformer, bridge rectifier, smoothing and analogue regulation approach. Often the PSU is much bigger and heavier than the rig itself, but you can be absolutely sure that there won't be any nasty surprises!

i do like that

[Albert H]

Radium - it's the right way to do it! Most higher quality transmitter designs use traditional power supplies. The downside is that bigger mains transformers and smoothing capacitors (in particular) are getting expensive. However, sometimes a little lateral thinking can get good results:

Some years ago, I built a whole run of transmitters into Car Battery Charger boxes. These metal-boxed Chargers (from Halfords for ~£10 each) had a mains transformer with a secondary winding that gave ~12.5 VAC at up to ~7 Amps. These - when full-wave rectified and smoothed - gave 16V DC at up to 6 Amps easily. This supply would power a 70 Watt rig with ease, and I found a large supply of 45 Watt 12.5V BLW60C transistors for not much money. I developed a push-push amplifier that would lope along virtually cold at around 70 Watts output. There was plenty of room inside the box for an exciter in a tinplate box and the 2-stage PA. I had a ready supply of heatsink extrusion, and could cut out a heatsink that would cover almost the whole of the front face of the box, and cover up the hole where the ammeter had been! I built loads of those little 70 Watt rigs with shiny chromed handles on top! My local Halfords couldn't understand why I wanted lots of those battery chargers!