RF Pro-1B Issue Developing

mbott

Greetings, I'm using the Pixel RF Pro-1B mag loop antenna with my KiwiSDR and my other radios. It has helped me fight off the local noise that I'm attempting to deal with, but last night for the second time I observed something I cannot explain. As the evening wore on here, the MW portion of the coverage seemed to disappear from the Kiwi and every other receiver attached to the RF Pro-1B. It's as if I had engaged the PAR Electronics BCST-HPF high pass filter. But I hadn't. This morning, all appears "normal". When this occurred previously, I swapped out the RF Pro-1B for my Wellbrook ALA1530LNP NA for a bit. I've not observed anything like it with the Wellbrook. Since the Wellbrook is a part of my "portable ops kit", I'd rather not need it for the Kiwi and others. Has anyone had a similliar experience with the RF Pro-1B?

Thanks!

--
Mike

WA2ZKD

That's what I run and I suspect you've been whacked by some close by MWBC station shifting to the night-time mandated pattern. I have several very high level MW stations near me, the Pixel shrugs them off and I filter downstream

WA2ZKD

this is close to you, but seems too low in power https://transition.fcc.gov/fcc-bin/amq?list=0&facid=22341

mbott

James, thank for the reply. Discovered just after noon local that the MW band was gone again. So for now, I've pulled the RF Pro-1B in favor of the Wellbrook and I'll keep a closer eye on things for a bit. I'll also pull the RF Pro-1B apart to look for signs of any moisture or other internal damage that may be at the root of this. As I said above, since the Wellbrook is a part of my "portable ops kit", I'd rather not keep it on the pole, but this may also provide the opportunity to get a W6LVP loop as a Wellbrook replacement.

--
Mike

WA2ZKD

If there's a diurnal pattern to the problem, that points to an external issue. My Pixel is used here http://www.wa2zkd.net:8073

mbott

Not sure if there is a pattern or not. I'll check it over after talking to the good people at DXEngineering in the next couple of days. A new preamp is $180 which is cheaper than the W6LVP I had in mind.

--
Mike

mbott

I broke down and ordered the replacement preamp.

--
Mike

mbott

The replacement arrived yesterday, and the observed drop outs of MW have not reappeared.

--
Mike

sesykes71

Is the preamp potted? Maybe you can find out what the problem is.

mbott

I think half the worlds supply of silicone was used to seal every seam and screw.

--
Mike

G8JNJ

>
>I think half the worlds supply of silicone was used to seal every seam and screw.
>

So the magic smoke is probably still contained within :-)

At least you can unpick silicone, go on you know you want to do it, and we all want to see what's inside :-)

Regards,

Martin - G8JNJ

mbott

Appears I was just being a bit too cautious opening the preamp. I'll have to back away from "half the worlds silicone" just a bit.

--
Mike

G8JNJ

OK, well that looks like it could be fixed :-)

Bit of low pass filtering then into a balun followed by 2 x Norton input stage (Q1/2) followed by what seems like a fairly standard push pull broadband amplifier with the transistors hidden under the tabbed heatsinks.

I'm sure I've seen a circuit of the Pixel RF Pro-1B somewhere on the web, but can I find it now........

Regards,

Martin - G8JNJ

mbott

"I'm sure I've seen a circuit of the Pixel RF Pro-1B somewhere on the web, but can I find it now........"

Been looking also.

--
Mike

WA2ZKD

It's a Jack Smith design...

KA7U

I'm curious why it needs a follow up amplifier. The Norton front end should have provided sufficient gain for a receiver. I built a couple of these, https://easyeda.com/doxnairobi/Norton-2N5109-LNA , and the gain was more than sufficient. I found attenuation was needed. Maybe The Pixel amp uses lower gain to improve IMD and noise and then ups the signal with a low gain output amp? The heat sinks would suggest power out though. I'm curious.
Ron
KA7U

Powernumpty

As the owner of a few things that have got hot over time I'm going to nominate the transistor on the back of the top heat sink, I'd look at the clearance around C20 too in case it is shorting when things get warm...

Also the goop around the left connector is not complete but the box is sealed with silicon so may have drawing moisture as the temperature cycles.

sesykes71

Jack Smith told me that it has more gain than any of his other amplifiers. Remember it is a shielded mobius loop which has lower gain. I would power it up with small signal on the input and measure the output while tapping on the components and or heating/cooling them to see if you can cause the failure.