Messages

421

The RF Workbench / Re: Class D output match

« on: October 08, 2019, 0002 UTC »

If the efficiency stays the same, then most likely we are dealing with either output transformer saturation, or more realistically not enough dead time in the PA drive phases causing shoot-through (overlap).  The output miller capacity canl cause the drive waveforms to stretch on turnoff, causing overlap and loss of efficiency.

As far as AM stereo is concerned, the exciter provides phase modulated RF to the transmitter (or PA) and an envelope signal.  The transmitter combines the two to produce an C-QUAM signal.  This is the way AM stations have been doing it for 30 or more years.  You can also use this method to produce other signals, such as DRM, SSB, etc.

+-RH

422

The RF Workbench / Re: Stretchyman 40w GaN TX is sick

« on: October 07, 2019, 2334 UTC »

I have a cheap-o PS I got from amazon. Its really stable and has its own variable fan. Says it can do up to 15A.

I don't understand why so many people buy those unbranded Chinese power supplies. I've seen many of those malfunction.
I could understand if the price was significantly cheaper, but IT IS NOT.

You can get a good quality meanwell of that power level for $30
$19 vs $30 bucks isn't a big deal.

https://www.trcelectronics.com/View/Mean-Well/LRS-350-24.shtml

Once you get into the higher wattages, then it makes sense. For those higher powers, eltek flatpacks, and Chinese Velikas are good.
https://www.aliexpress.com/item/32835899833.html

Sorry to get off topic. I'm done.

Agreed.  Mean Well is as bottom of the barrel as I'll go.

+-RH

423

The RF Workbench / Re: IXYS-RF better than GaN?

« on: October 07, 2019, 2331 UTC »

Both datasheets date to 2009 and use conventional mosfet technology.  All the places I checked list them as obsolete or NLA.  At close to 2000pF, they will be hard to drive, and at only 8A of continuous drain current output power capability will be limited.  Modern SiC devices are much better in almost all of the above metrics, and are available from a multitude of vendors at low cost.

+-RH

424

The RF Workbench / Re: Stretchyman 40w GaN TX is sick

« on: October 04, 2019, 1818 UTC »

 ...and I've got my own conspiracy theories about you and your extraordinary repair policy, so there.   

Here's a nice video of the method I used to test the mosfet with my multimeter:
https://www.youtube.com/watch?v=tL7bQuJaXKA


Gotta love (not) the stand w trump and epoch times ads you get when you click that link.   

~

Serves you right for not running adblock

425

Huh? / Re: If anyone is looking for a radio show idea...

« on: October 04, 2019, 0554 UTC »

Facebook.

+-RH

426

The RF Workbench / Re: Stretchyman 40w GaN TX is sick

« on: October 03, 2019, 2126 UTC »

These modern transmitters have a lot in common with switching supplies...both operate in switch mode (class D or E) and the waveforms feeding the power devices have to be right or the smoke comes out.  I too spent a few years working on SMPS's exclusively and the first thing you did before bringing up the mains was testing the drive waveforms.  If they don't look right, your mosfets won't last long.

I understand the frustration, but you need the have the tools and know-how to work on these things.  Its not like the tube days when you could swap a tube or two and see what happens.  More often than not in solid state, you're greeted with pops, bangs, and puffs of smoke.

+-RH

427

For Sale / Wanted / Barter / Re: Wanted TPA3116D2 Amplifiers

« on: September 30, 2019, 1829 UTC »

Your first mistake was designing something around a third party board from the orient...  One-off are the way those folks roll, usually around someone else' design.  At this point your choices are either drill new holes in the case to accept a different board, or roll your own and move on.

Simple!

+-RH

428

For Sale / Wanted / Barter / Re: Wanted TPA3116D2 Amplifiers

« on: September 30, 2019, 0636 UTC »

Why don't you just roll your own?  A slack handful of parts and the IC is all you need.  The datasheet provides the application circuit.  You would even build it into your existing exciter board.

+-RH

429

Shortwave Broadcast / Re: Voice of Korea - transmitters

« on: September 28, 2019, 0812 UTC »

an I/Q recording would be helpful in determining the nature of said beast.  AMSS might sound similar to this as well.

+-RH

430

Shortwave Broadcast / Re: Voice of Korea - transmitters

« on: September 27, 2019, 0444 UTC »

Do you actually see carrier frequency shift on the waterfall or spectral display?  It sounds to me like slow speed data, or background noise in their audio chain.

+-RH

431

General Radio Discussion / Re: Proposed Termination of USCG Medium Frequency NAVTEX

« on: September 27, 2019, 0433 UTC »

".....perhaps they could increase efficiency in the tx and antenna system to save money if that was the priority? Of course, new, higher efficiency equipment's going to take money too."

Since when was the government interested in saving money?

..Just a thought.

+-RH

432

The RF Workbench / Re: I need some help writing some arduino code for RS232

« on: September 22, 2019, 1820 UTC »

The control point and transmitter will be separated by some distance, and a RS232 link exists between those points.

+-RH

433

North American Shortwave Pirate / Re: XFM 6275 AM 0115 UTC 22 Sep 2019

« on: September 22, 2019, 0212 UTC »

I wish 60 meters was possible, but I only have the 48/43M antenna here tonight.

Band switch will be happening soon, but with the amount of storm noise out there tonight, 73M might be unlistenable anyway.

+-RH

434

The RF Workbench / Re: Class D output match

« on: September 16, 2019, 2018 UTC »

Oh for Cwuam surely a DtoA and a linear...?

Nope, tradition high level PWM with phase modulated carrier drive.  All the pre-correction is done in the exciter.  The old transmitter was linear all the way from 0dBm to 400W carrier, at about 30% efficiency.  I'm trying to get away from that...

+-RH

435

The RF Workbench / Re: Class D output match

« on: September 16, 2019, 1938 UTC »

Until it can do cquam or other modes, no thanks.

+-RH