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Messages - redhat

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31
Part 15 AM and FM Station Operation / Re: Music licensing concerns
« on: December 22, 2022, 0804 UTC »
Music licensed for broadcast may or may not include licensing for recordings of the same broadcasts.  This all depends of the terms of the right you pay for, and is handled through ASCAP or BMI usually by a third party like sound exchange.  In regards to Art Bell, rumor is he had some sweetheart deal for royalties, which is why there was so much music in his shows.  This may have changed when George Bory took over the show.  They may have secured broadcast rights for the music, but not recorded rights.

I could be wrong, but that's my understanding of how it works.

+-RH

32
VFO's tend to drift radically based on temperature, applied voltage, circuit loading, etc.  Unless great pains are exercised in construction, the drift of a conventional VFO can be significant.  One of these circuits appears to be a modulated power oscillator, meaning the operating frequency would likely change based on antenna loading changes, and with modulation...poor man's FM.

It's one of the reasons I like DDS 😁

+-RH

33
I used W1VD's design as the basis of my work.  All I did was remove the 1:4 output transformer and directly couple the tank to the balun.  This, with a change to modern SiC devices, makes it possible to get kilowatt level carrier power from just two devices.  In my current design, the balun has been replaced with a hardline transformer wound into the tank coil, the outer being the primary as well as the tank inductor, the inner being the output winding.  The RFC's don't seem to be real critical, just aim for 10x reactance of the nominal line output impedance.  Doing these modifications raises the PA modulator impedance to around 10 ohms or so, easing current carrying requirements at high power.

+-RH

34
North American Shortwave Pirate / Re: XFM 4185 AM 0104 UTC 18 DEC 2022
« on: December 18, 2022, 0746 UTC »
Considering the second harmonic on the transmitter is measured at better than -50dBc, It is MUCH more likely you heard an image created within your receiving system.

Thanks all for making the best of a cruddy night.  Much enjoyed on this side of the mic!

+-RH

35
General Radio Discussion / Re: Garage Door Opener Damaged by HF RF?
« on: December 11, 2022, 2225 UTC »
Interference is more likely than damage.  Get an SDR or spectrum analyzer and see if there is anything strong near (or a sub-multiple of) the frequency of operation.  Once upon a time, I had an FM pirate on the roof of a house in suburbia.  Whenever the transmitter was on, the garage door remote wouldn't open the door.  I did some measurements and found out that the 3rd harmonic of the commercial transmitter was a little high.  I put a quarter wave stub on the transmitter and the garage door went back to normal.

I have had HF mess up microprocessor based things, but they usually don't work again until you power cycle them.

+-RH

36
General Radio Discussion / Re: Garage Door Opener Damaged by HF RF?
« on: December 11, 2022, 1438 UTC »
Fwiw, I've had rf from my test transmitter at the house kill cheap led bulbs....

+-RH

37
The RF Workbench / Re: Heathkit DX-40 tube transmitter
« on: December 06, 2022, 2300 UTC »
Max Carter has some notes on his website about 'guilding' small ham tube transmitters for better audio.  Notes here http://maxmcarter.com/hg303/index.html

+-RH

38
My 'daily driver' PA has a drive delay and protection circuit onboard, and seems fine up to 10MHz or so.  I haven't investigated any higher as I feel there is little merit in doing so, and have no interest in anything above 30 meters.  The simple drive circuits consisting of just an xor configured as a phase splitter start having efficiency drop off after 4 Mhz.  This makes sense as the drive pulse distortion begins to be a larger fraction of on time with increased frequency   Granted this was a PA I built several years ago now and there are other devices and drivers to try.

+-RH

39
:shrug: It doesn't seem to matter much until you get over 4 MHz, then things get hairy, and efficiency tends to nose-dive.  My main transmitter has overlap control and drive loss protection, FWIW.

+-RH

40
Quote
A simple Russian as a human will share with you his last loaf of bread and a bottle of vodka.

We should all be so lucky.  Loving this thread, and hope to learn more as this develops :)

спасибо!

+-RH

41
Quote
These parts have low breakdown voltages which probably forces you into using a CMCD architecture, as opposed to a Class E architecture, in order to get the RF output power you are claiming, because of the peak drain voltage excursion in Class E. Nothing wrong with CMCD (I'm actually doing some myself) but it does bring a slightly higher complexity, with the need for a non-overlapping clock generator/due diligence to make sure you aren't cross conducting and some sort of output balun, be it a traditional wound one or an LC balun, because at these power levels the typical output impedance is significantly less than 50 Ohms.  On the other hand, if you are intent on using a low BV transistor in Class E, a cascode architecture should work.

Actually, the voltage difference is not all that great.  Class E is around 4x Vcc, CMCD is around 3.14x in my experience.  There are plenty of good devices in the 600V class now that will work nicely in either architecture.  Also, dead time control is nice but not necessary for push-pull operation.  I've had PA's running at 80 meters or so with no dead time control circuitry.  I even built a 2 mosfet 500W MW PA that is running in commercial service with just a 7486 setup as a phase splitter...no drive loss protection though  :-\

For me one of the appeals of CMCD was the elimination of most of the cumbersome ferrite in the output section.  I even started using hardline (0.141") coax as a combination tank resonator and output transformer.  No ferrite required!  Typical PA impedance with respect to Vmod is on the order of 10 ohms or so, assuming the PA is looking into 50 ohms.

+-RH

42
General Radio Discussion / Re: Hobby Broadcasting Radio
« on: November 19, 2022, 2012 UTC »
Agreed, and thanks for putting this together for us out here!  I also echo the comment about using Archive.org for distribution.

+-RH

43
Shortwave Broadcast / Re: WTWW the truth
« on: November 16, 2022, 0132 UTC »
From what I heard, the church was picking up the tab on the power bill.  The underwriting they had likely wouldn't have covered the power at several hours a day anyway.  I guess we'll see what happens, if anything once the dust settles.

+-RH

44
Shortwave Broadcast / Re: WTWW the truth
« on: November 15, 2022, 2059 UTC »
It costs too much to run hi power 100KW inefficient transmitters with the power wasteful AM carrier anyway. The minimum for US shortwave is around 50KW for AM intended for international broadcasting. Other countries have a much lower minimum power requirement.

Your assuming that these stations are running at full power.  I've been to several shortwave broadcast facilities over the past decade, and not one was running at more than 50 percent power.  I get it, power is expensive.  Also, parts for most of these transmitters are either expensive, unavailable, or have long lead times.  We are not living in the 1950s either.  Modern transmitters with solid state modulators approach 80 percent ac to rf efficiency.  It does get expensive if your are running 24/7 operation though.  Few stations are doing such.

+-RH

45
Shortwave Broadcast / Re: WTWW the truth
« on: November 14, 2022, 0241 UTC »
Anybody professing to provide the truth with only one post to their credit is highly suspect in my book.  I smell a sock puppet!

+-RH

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