Who makes these?

[Shedbuilt]

There's been a lot of talk about the SRF261, which seem to have appeared cheaply, from a number of sources. The package, power, and voltage look similar. A bit of a stab in the dark, but could be....

[Shedbuilt]

Agreed on the comments about gate voltage. 1) Yes, the original (assuming it was one of the LM2596s), would have been the adjustable (ADJ). I'd only ever dealt with the adjustable ones before - didn't know there were fixed voltage versions. Easy to say with hindsight, but in cases like this, especially if you're changing for an unknown regulator, try to find a way to disconnect the output before turning it on, then switch it on, and make sure the voltage is sane, before connecting to anything sensitive. Also agree that using a variable supply to test (after changing the FET if it's definitely blown), and starting off at 0, is a reasonable alternative approach.

[mixfm]

bin it, sprog box

[XXL]

bin it, sprog box

Did you buy one of these ? Yes they do sprog but not much. Can only hear it right next to the tx site. Luckily there was nothing on the frequencies it was sprogging on.

[King Croccy]

bin it, sprog box

Did you buy one of these ? Yes they do sprog but not much. Can only hear it right next to the tx site. Luckily there was nothing on the frequencies it was sprogging on.

I've seen them on Aliexpress, is that the 120w or 200w?

I've only ever seen the 60w and 150w Chinese transmitters up close. Harmonically they were fairly clean however if you dropped the power (both were variable), all these spurs started coming out of the noise floor (in band) till it was a dirty piece of crap!

Is it not possible to mod the board to take a different mosfet? I doubt the Chinese will tell you the part they are using. The design is very similar to those "180w kits" that you used to be able to get on Ebay. Although the mosfets they used were not great (mrf186 inefficient, mrf9180 unreliable), it might get you out of jail and back on air.

[BlackBeard]

Hi I have one of these china 200w fm transmitters but the regulator is popped from accidentally connecting the polarity the wrong way round. Can anyone confirm what voltage it could be ?

30E93493-4C08-4623-AA46-CEA047676C79.jpeg

Saw those on Aliexpress as well. Just out of curiosity, is it powered by one of those all-in-one BH/BA/Quintic-chips? Or does it have a real VCO/PLL or DDS? Does it have a MPX input?

Did you check the harmonics, XXL?

[XXL]

I haven’t looked into the circuit much, and it’s under a metal screen soldered to the board. I didn’t check the harmonics but at the transmission site I can get it on several other frequencies around the broadcast frequency, but they don’t go far, maybe 200m and they’re gone.

[BlackBeard]

I haven’t looked into the circuit much, and it’s under a metal screen soldered to the board. I didn’t check the harmonics but at the transmission site I can get it on several other frequencies around the broadcast frequency, but they don’t go far, maybe 200m and they’re gone.

XXL, I have good news for you. I asked the seller "TZT Direct Official Store" the following question about the transmitter you're fixing:

Friend, how is the RF-signal generated? Does it use an IC-chip like BH1415F or QN8066? Or does it use a DDS chip? Does it have a MPX-input? Can I use RDS on this transmitter?

He replied: 1418 chip, no MPX input, can be modified

I suppose the tx is using one of the BH1418xx-chips. Or is there another chip called "1418"? Dunno how clean it is and how exactly the RDS "can be modified". Maybe the IC is only used for stereo encoding (which would be better) but I suppose that it's used for everything - at least it would make sense concerning the spurs.

[XXL]

Really ? When I asked them they wouldn't give me any info at all. And I have successfully got RDS to work with this. I had to remove a few caps or resistors (can’t remember) from the audio input path.

[XXL]

Also you need a seriously beefy power supply to run these. 600w wasn’t enough. I had to use 1000w supply.

[BlackBeard]

Really ? When I asked them they wouldn't give me any info at all. And I have successfully got RDS to work with this. I had to remove a few caps or resistors (can’t remember) from the audio input path.

Interesting. Can you send a photo of the RDS-mod?

It's a pity that those modules are still quite expensive - 405€ on Ali/385€ on Ebay incl. shipping - otherwise I'd get one to play around with. If you add the cost for a PSU + case, it'd be about 500€ in total. For that money you can almost build a solid 300w rig with pre-made components from Dutchrfshop, Amateurradioshop and an exciter from JPL995 - without the need to solder anything critical. The chinese module's price compared to it's benefit kinda makes it obsolete.

You said that you got it on your table for a repair job, right?

[XXL]

yeh but if you purchase a built rig from anyone its always going to be at a labour cost and inflated price.