[Elecraft] Noise from KAT500?

[G4GNX]

FWIW I had this issue with an IC7100/MFJ 1500W tuner.

I was finding sprogs in the 40 metre band and they were changing frequency (moving round the band) when I changed the tuning frequency, which I put down to different relays being deployed, varying the load.
I replaced the PSU and all returned to normal.

I also have an AOC monitor that chucks noise over several HF bands on my K3S, due to an errant PSU. I don’t use it very often and not in the shack any more.

I run my K3S and ancillaries (including the KAT500) from a 60 amp (continuous rating) variable voltage SMPSU which is capable of 100 Amps for short periods. It’s well built and very quiet. That PSU has been in use for many years with no hint of trouble. I also use them on Theatre Organ consoles for the stops. There can be upwards of 400 stop magnets requiring 500mA each, usually for <50mS, so theoretically 200A could be drawn and on the odd occasion (usually under test) that a General Cancel is required for all tabs (stops) those PSUs just take it in their stride, and there’s been no QRM noticed on any nearby radio.

SMPSUs are absolutely fine if you choose carefully - the bigger the better. Wall warts are just a recipe for trouble. The only ones I use these days were supplied by Yaesu, rated at 12V 1A and they’re quiet across all loads I’ve presented them with.

Pleased that you’ve cured your issue.

73,
Alan - G4GNX
South Coast UK
Elecraft K4D / KPA500 / KAT500 / IC-9700




> On 3 Dec 2023, at 01:48, W2HX <w2hx at w2hx.com> wrote:
> 
> Mike, K8CN wins the cigar!
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> 
> 
> The issue is the power supply ☹ I took some spectrum analyzer plots to 7 MHz and you can see what I saw. The set up is spectrum analyzer -> KAT500 -> Dummy Load. First picture are two "max hold" traces superimposed where the problem can be seen.
> 
> https://w2hx.com/x/Elecraft/KAT500/Noise-Issue/KAT500-AC-Power.png
> 
> The "lower" trace is what I saw with the kat500 in bypass. The "top" trace is with the kat500 inline (auto or manual).
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> 
> 
> I then replaced the wall-wart power supply with a 12V battery. And this is what I saw for BOTH bypass and inline. Clearly the problem.
> 
> https://w2hx.com/x/Elecraft/KAT500/Noise-Issue/KAT500-battery.png
> 
> using a battery, the noise is about -80 dBm. Using the wall-wart, in some cases the noise is as high as -60 dBm
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> 
> 
> My task now is to either leave it on battery or preferably, find a low noise PS.
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> 
> Thanks everyone for the ideas.
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> 
> 73 Eugene W2HX
>