Messages

16

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

17

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

18

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

19

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

20

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

21

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

22

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.

23

General Radio Discussion / Re: Scoop: Congress moves to preserve AM radio in cars

« on: May 21, 2023, 1937 UTC »

If their intention was to mandate HD reception, they wouldn't have the exemption for all-digital reception.  As most laws, it is vague and confusing for a reason.

+-RH

24

General Radio Discussion / Re: Scoop: Congress moves to preserve AM radio in cars

« on: May 21, 2023, 1650 UTC »

There is an exemption that does not include all-digital AM, but implies hybrid mode must be supported.  This sounds to me like HD AM demodulation is not required.  Thus, as long as conventional AM is supported, the vehicle meets the requirements of the act.

+-RH

25

General Radio Discussion / Re: Scoop: Congress moves to preserve AM radio in cars

« on: May 21, 2023, 0622 UTC »

Nevermind FEMA has dumped untold millions into hardening transmission facilities in the fleet of EAS PEP AM stations....

I'm sure the government wouldn't want to see that money wasted..oh wait.

https://rbr.com/homeland-security-installing-transmitters-nationwide/

+-RH

26

Software / Re: For those whom like to use software audio processing.

« on: May 17, 2023, 0546 UTC »

My main processor these days is Stereo Tool running on a Raspberry Pi 4.  The declipper is mandatory with newer music.  I think with the options I bought for AM with advance dynamics and declipping, it was about $200.  Telos licensed the declipping algorithm from Hans, the developer of Stereo Tool.  They call it 'undo'

+-RH

27

Amateur Radio / Re: HAM – Official Documentary 2022? SWL'ing rip.

« on: April 30, 2023, 1718 UTC »

I keep seeing it show up in my YT recommends....yawn.

+-RH

28

General Radio Discussion / Re: DaveP passes

« on: April 27, 2023, 0040 UTC »

Dave was a good guy.  We had many exchanges over the years about his not-so-low-power AM he ran at home, and other projects.  He will be missed by all of us.

+-RH

29

General Radio Discussion / Re: Song Info TX mode

« on: April 08, 2023, 0546 UTC »

I would run PSK31 just outside of your audio modulation.  If your running AM, you can simply inject PSK31 into the baseband audio just beyond your program audio bandwidth at about 10% modulation.

I assume the purpose of this is to provide a similar service to RDS on HF?

+-RH

30

The RF Workbench / Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter

« on: March 18, 2023, 0451 UTC »

The ones I have are DROK or a clone off amazon, and they work fine up to 15-17W carrier and don't cut out until you hit 29VDC input.  The PA's I run are around 10 ohms at the DC input.  The small boards seem better than the larger ones.  I bought one of the larger 100W amps, and upon closer inspection found it had a small IC in it from a LCD TV, which also didn't pass DC.  Caveat Emptor indeed.

+-RH