Messages

1

The RF Workbench / Re: My attempt at a breadboard quadrature modulator for MW

« on: June 26, 2024, 1818 UTC »

Apparently I don't have any schemos for the old stuff I built.  I can throw something together, but the through hole versions of the 1496 are NLA.  They are still available in SMD.  Do you have SMD capability?  It might be easier to roll a small board for this.

+-RH

2

General Radio Discussion / Re: Buying Airtime For An Uncensored Radio Show?

« on: June 15, 2024, 0422 UTC »

Post a link to your shows somewhere on here.  If its any good, folks will pick it up and relay it for you, likely for free

+-RH

3

The RF Workbench / Re: What's the highest frequency people have tested IRF series MOSFETs?

« on: June 08, 2024, 0040 UTC »

In commercial designs, 13-15 MHz is about the limit for power devices in the 500W class.  Smaller fets you should be able to run quite a bit higher, although 40-50 MHz is likely the practical limit.

+-RH

4

The RF Workbench / Re: Would a breadboard I/Q modulator be practical at MW frequencies?

« on: June 04, 2024, 2045 UTC »

I've built prototype MW AM stereo modulators on breadboards in the past, and it worked.  With digital modulation properly filtered in the digital domain, the only issues you will likely have is spectral regrowth, ie out of band emission.  This is measured relative to carrier level, and at present -40dBc is considered acceptable.

COTS solutions may exist, but I don't know of any at a reasonable price.  If you need some schematics to get you going I can pull some stuff from my archives.

+-RH

5

The RF Workbench / Re: Low-cost RF synthesizer uses generic ICs?

« on: May 24, 2024, 0131 UTC »

This is faster and not limited to the step size of your divider.  I've used these to driver commercial transmitters, am stereo exciters, as well as my own rigs.

https://www.ebay.com/itm/186071392182

+-RH

6

Equipment / Re: 32 Quartz Crystal Unit Manufacturers in 2024 ? Good!

« on: April 01, 2024, 1335 UTC »

All of the companies on that list are large manufacturers located overseas.  No doubt Kyocera or Abracon can make you an SMD crystal, but you'll have to order 100,000 units.

Domestically, you can try Bomar.  If its a common part, they can job shop it overseas and have them made in small quantities.  In this day though, better to look at other options than crystals.
http://bomarcrystal.com/

+-RH

7

The RF Workbench / Re: 15-Watt SHORTWAVE BROADCAST TRANSMITTER

« on: December 30, 2023, 2239 UTC »

FWIW, the top of all pages reads...

"We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale."

Chris just doesn't want to deal with the legal liability of allowing commercial traffic of questionable goods on his site.  He pays the bills, that's his right to do so.

You also have proven over the years to be rather obtuse and abrasive when confronted with concerns about your commercial activities, and that leaves a bad taste in peoples mouths.

+-RH

8

The RF Workbench / Re: If you are great at rollin' your own DIY RF Gear, check this place out!

« on: October 13, 2023, 1647 UTC »

They have listings all over ebay as well.

+-RH

9

SDR - Software Defined Radio / A theory on Kiwi TDoA ambiguity

« on: September 06, 2023, 1639 UTC »

I was thinking about this last night over dinner.  I think the reason the TDoA function on Kiwi's doesn't work all that well is pretty simply;  There are no two Kiwi's with identical antennas, and more importantly, antenna cable lengths.  A few nanoseconds here and there can cause pretty severe distance errors.

If we had a network of Kiwi's with all the same antennas and cable lengths, I bet the results would be more predictable.

Thoughts?

+-RH

10

Huh? / Re: FCC Advances FM HD Power Proposal? Oh boy...

« on: August 11, 2023, 1856 UTC »

The proposal would not raise the current HD power ceiling, which is -10dBc, or 10% digital ERP relative to analog ERP, but instead allow the use of asymmetric sideband power on a non-experimental basis.  They are beating a dead horse at this point.

+-RH

11

Equipment / Re: FYI on the QRZ swapmeet page-- Gates BC-1H 1kW Broadcast Transmitter free

« on: August 10, 2023, 0859 UTC »

The Gates 1KW class AM transmitters mostly used triode tubes, 833A's which are stubborn as a mule on higher frequencies.  Later rigs from other vendors (ITA, RCA, CCA, et al) used tetrodes, which were easier to drive, and didn't require neutralization.  These transmitters would be better candidates for HF service.

+-RH

12

Huh? / Re: A 1MW MW transmitter coming to Pakistan? Looks like it.

« on: July 31, 2023, 0216 UTC »

Actually, TV ERP's went down with the conversion to digital.  What used to be a 3-4MW ERP UHF is now about 1MW.  There is one caveat; analog TV power was measured in PEP essentially (sync tip power) whereas DTV is measured in average power.  When factoring in the crest factor of the DTV waveform, ERP's are still about 2x what they once were.  The power limits are dependent on frequency range, as the equivalent service contour on a UHF TV station requires more power than VHF low and VHF high.  People used to put up with the noise in the picture to watch TV.  I remember sitting on the floor of my grandparent's farm in the midwest and watching snowy TV from far away, because there was nothing else.  Digital of course has the cliff effect.  The SNR required for the receiver to decode the datastream is much higher than what we would tolerate in the analog days.

+-RH

13

General Radio Discussion / Re: AM STEREO

« on: June 26, 2023, 1857 UTC »

Decoding C-QUAM as QAM eliminates much of the platform motion with a bump in low frequency distortion caused by intermodulation.  There were hacks to the older C-QUAM demodulator chips where you could disable cosine correction and force the chip into QAM mode.  In software this should be easy to do, and when the Kiwi folks added CQUAM demodulation, I advised them to add a QAM mode to get around the platform motion issue.  I'm not sure that this was done, however.

On HF, ISB would likely be a better choice.  You still would have phasing effects, but the complete channel reversal and wobble under fading conditions would go away.  I chose C-QUAM initially because of receiver support.  At the time, there were no software decoders available for ISB, and to date the only one I'm aware of is onboard the Kiwi.

+-RH

14

The RF Workbench / Re: Oscilloscope recommendation?

« on: June 17, 2023, 1629 UTC »

I have two Rigols.  The later ones are software limited, but can be hacked

+-RH

15

North American Shortwave Pirate / Re: AM Stereo 1620 6955 AM 0130 UTC 9 June 2023

« on: June 09, 2023, 0738 UTC »

In the chance any of you folks ever hear a pirate claiming to be using "Kahn" or "Kahn-Hazeltine" AM-stereo, switch the Kiwi to SAS mode. I have yet to hear a pirate doing Kahn.

As with C-QUAM, there is a pilot tone with the kahn system as well, at 15Hz, Magnavox was 5 Hz.  This would be another tell-tale of stereo transmission.