Nasty

[bristolpirates]

What you are seeing here, is the signal from a rig that's just come down the road from me, as displayed in SDR Sharp. It's obviously not an RSL, though it is on 87.7. It's relaying an automated Bulgarian station. It's in mono, no RDS. Audio distorts slightly.

The main signal is accompanied by many harmonics which spread out from 87.5 to 87.9 either side of the main signal. Compare it with the Radio 2 relays from 88.1 onwards, and you'll see what I mean.

It's at 30dB on the Tecsun when I plug the same aerial that feeds the SDR into that (not simultaneously). 30dB isn't that strong really, yet I can still hear it's 1st harmonic on 175.4MHz.

This isn't the SDR being overloaded, because there is a 25W community station which is stronger, not much further away, and that doesn't cause these harmonics.

What a mess!

[Albert H]

That's one of those nasty Chinese rigs! They're often based on the little "audio-sender" ICs that were designed for a milliwatt or two, to allow you to transmit the output of your iPod or CD player to your car radio. The Chinese thought that it would be acceptable to amplify these toy chips up to several Watts, and you've seen the results.

[bristolpirates]

Yes, this is the worst example I've seen. I've been sat right on the doorstep of some before, and never seen that cluster of harmonics around the main freq before. Strange that it's in mono though, these things are usually stereo because that's what the chip does. The audio certainly has that slight clipping sound to it that those rigs have, even though it seems it's down reasonably low.

It's switched off for the moment, so hopefully it won't be on often.

[Maximus]

Definitely looks like a Chinese rig. I'm surprised it's not in stereo though.

Used one for about a week, many years ago. Soon replaced it with a proper rig.


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[thewoodstarr]

Not nice....

[thewoodstarr]

Don't use those USB all in one so called Spectrum analyzers, cos they are rubbish. But even so, that looks like a Jammer! Fuck me. Do not use not use that mate. You will get a visit at least by your neighbors!

[thewoodstarr]

Don't use those USB all in one so called Spectrum analyzers, cos they are rubbish. But even so, that looks like a Jammer! Fuck me. someone would have got a knock at least by the neighbors!

[bristolpirates]

I don't own this thing, it's somebody just under half a mile away using it.

The next day, for some reason they'd dropped the power right down, and I could only get it with the loft aerial. The harmonics couldn't be seen/heard here then. Wasn't on this weekend at all to my knowledge, unless they've dropped the power even further.

[Maximus]

They probably blew the HVF1 output transistor.


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[bristolpirates]

This came back at the weekend. Quite a bit of adjustment going on. The signal was better than last time but quickly developed problems and faults. Bit of a long boring vid, but you can see the problems develop over the course of the day:

[bristolpirates]

God. Damn.

Two rigs now, mixing products, the lot...

[Maximus]

Either your RTL dongle is being swamped with high field strength or they’re putting out a right mess.

I’m voting for the second as my dongle works fine with a 150w rig next to it.

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[thewisepranker]

I’m voting for the second as my dongle works fine with a 150w rig next to it.

Into what, though?

[FM King]

Those SDR things are terrible when it comes to picking up crap near by, try also checking on a scanner.

[Maximus]

I’m voting for the second as my dongle works fine with a 150w rig next to it.

Into what, though?

Good point. It was going into a half wave about 15m away and the dongle didn’t have an aerial connected.


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[bristolpirates]

Either your RTL dongle is being swamped with high field strength or they’re putting out a right mess.

I’m voting for the second as my dongle works fine with a 150w rig next to it.

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Yeah, the local community station, same distance away but opposite direction, stronger signal, doesn't swamp my SDRPlay or RTL dongle. It's definitely all their mess. The sprog on 88.8 comes across on the Tecsun too for example.

[Albert H]

I've been playing with an "Ebay special" SDR. It's surprisingly good, and covers DC - Daylight (almost!). It came as a kit, with a PCB, a USB TV receiver dongle that had to be stripped apart, a couple of "F"-type sockets, a bag of components and a pre-drilled aluminium box. It took about 1½ hours to build (I could do the next one more quickly) and the results were great. With an OTG USB adaptor, it'll plug into my Android phone, and there's software for AM, FM and DAB reception. I'm not certain how well behaved it's likely to be next to a high-powered rig, but it's certainly an interesting receiver for use on those site-seeking road trips, trying to see where we can "hear" the link transmitter!

[Maximus]

It’s also worth spending an few quid extra and getting a TCXO stabilised dongle:

https://www.rtl-sdr.com/tag/tcxo/


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[bristolpirates]

I don't use a dongle anymore, although I still have one, my SDR is a little bit better. It doesn't suffer with so many images around Band 2 (although there are still plenty on other bands for some reason) and it's 12 bit so a bit more dynamic range. I've never had freq. stability problems with either the dongle or SDR.

http://www.sdrplay.com/

I travel around with my SDR and depending on location reception can be good or bad. I find most hotels have a lot of noise going on, and this causes some real problems. Better off finding a field on a hill, and hanging the aerial in a tree. Also, strong transmitters will overload it if they are within the frequency range you have selected. When I was in Bute Park in Cardiff and trying to use the dongle (not the SDRPlay at that point, hadn't worked out how to get it running on my tablet then), Wenvoe overpowered it very easily.