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Messages - redhat

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616

North American Shortwave Pirate / Re: Mix Radio International 6870 USB 2221 UTC 21 Sep 2018

« on: September 21, 2018, 2349 UTC »

6970.000 KHz 2346z S8-S9 with Seal's 'Crazy' Very nice 13K audio here.
2347z Sade 'Sweetest Taboo (Live Version!!)
2353z Mix Radio International ID
2353z Tears For Fears 'Change'
0000z Nice jazzy instrumental with some KILLER bass!! Love it, wish I knew what it was. (Per the Op, Chris Botti 'Back Into My Heart' Thanks!!)
0004z Dave Mason 'We Just Disagree'
0007z The Who 'Eminence Front' (Excellent tune!) Still hanging in at S9, storm noise is becoming more pronounced though.
0012z Rush 'Fly By Night'
0015z Joe Walsh 'Life's Been Good'
0024z 'You are tuned into the best of shortwave radio, mix radio international' ID
0026z Delfonics 'Didn't I blow your mind this time'
Storms getting too close, had to close down.

Recording from approx 0004z-0028z
https://drive.google.com/open?id=1V9Ct_bV5hbjl4xtvrUqQz0BgNi9BIkBw

Thank for the show!

+-RH

P.S. The Op emailed me and said they enjoyed the recording. Your welcome!

617

The RF Workbench / Re: A legal limit am transmitter for 75/160 meters from WO1U

« on: August 28, 2018, 2300 UTC »

Quote from: JimIO on August 28, 2018, 1857 UTC

I'm only talking about hobby/pirate stuff.

Why should we expect any less? I guess it boils down to operator philosophy, but I would rather carry something into the field that was designed with commercial 24/7 operation in mind. There is a better chance it will work when I flip the switch.

+-RH

618

The RF Workbench / Re: A legal limit am transmitter for 75/160 meters from WO1U

« on: August 28, 2018, 1701 UTC »

Some measurements you have to do with the power on. Gate drive waveforms can tell you a lot about the health of a mosfet and the load downstream. Lousy drive makes for lousy efficiency, and eventually burnout. Drain waveforms will tell you about parasitics and whether the output network is properly tuned.

Better information makes for better troubleshooting. Case in point, I just got my prototype transmitter running last night. The thing had survived a 3 hour excursion to 1200 watts carrier on 4070 KHz in the back yard a few months back. Following that I retuned it to 43M but never tested it at power. The next day I drove to a site and setup. When I flicked the HV switch, the PA failed, as indicated by a driver overcurrent condition. I brought it home and replaced all the silicon, brought it up to 250W with modulation, and it ran for about two minutes and failed again. Over the last few months of armchair troubleshooting, I theorized that some of the passive components must have been overstressed and developed partial breakdown problems that was taking out my fets. I again replaced all the silicon, and all the passive parts in the RF power path (DC blocking caps and resonator caps). In the process I decided to change out the output balun core and go back to material 61. I quickly discovered that I could not unwind the balun because the supposed teflon jacket on the coax had melted and several of the adjacent turns had punched through, as evidenced by soot marks here and there.

I still don't know if the passive components failed, but I changed them anyway. In light of the smoking gun, it seems they were fine. At this point its not worth the trouble to find out, especially since all Cree SiC devices across the board are out of stock until October and I have a limited stock of replacement devices.

BTW in any commercial transmitter, PAV, PAI, and FWD/REV power at a minimum are measured. This monitors not necessarily the peak voltage across the output devices, but the average DC input to the PA stage following the modulator. PAV and PAI are multiplied together, then multiplied against an assumed efficiency factor to determine power output. This is called indirect power measurement. Direct power measurement is carried out with a calibrated watt meter, or using calorimetry.

+-RH

619

The RF Workbench / Re: A legal limit am transmitter for 75/160 meters from WO1U

« on: August 28, 2018, 0111 UTC »

When playing with solid state, good metering is essential. PA Volts and PA Amps measurement will allow you to do indirect power calculations, and when compared to output metering provides a troubleshooting aid.

If you want to stay in the dark thats fine, but your going to have a lot of trouble trying to fix it when something isn't right.

+-RH

620

The RF Workbench / Re: A legal limit am transmitter for 75/160 meters from WO1U

« on: August 27, 2018, 1925 UTC »

Line isolation is not a big problem if you have transformer coupled output and drive signals. Above the 1KW (5KW PEP) or so level, this makes more sense than stringing together more switchers, both from a weight and cost standpoint. I see a lot of the high power Greek pirates doing this, and at the levels they are now pushing (12KW) the transformer required would be quite massive. It all gets rather complicated with regard to metering, in this case you would need analog photocouplers with the associated circuitry to get voltage and current samples to the outside world, isolated from the mains. Watch your signal grounds!

+-RH

621

The RF Workbench / Re: A legal limit am transmitter for 75/160 meters from WO1U

« on: August 26, 2018, 2241 UTC »

I'm sorry to see you go. I am glad you made this project available to all of us, and I certainly learned a lot from it when I was starting out building my own stuff.

Please don't be a stranger, and I hope you won't let this experience taint your opinion of the rest of us. We're all here to learn, some folks forget that.

+-RH

622

The RF Workbench / Re: A legal limit am transmitter for 75/160 meters from WO1U

« on: August 26, 2018, 2151 UTC »

I'm going to get some popcorn and watch this from a safe distance

+-RH

623

General Radio Discussion / Re: Who makes the QRM to pirate stations on 48 mb

« on: August 22, 2018, 0344 UTC »

Link appears to be broken?

+-RH

624

General Radio Discussion / Re: Logging Pirate Radio

« on: August 14, 2018, 1720 UTC »

Personally I have no problem with people submitting reception reports using remote SDR's. It is a welcome courtesy to note it in the report log, along with your and the receiver's location.

+-RH

625

FM Free Radio / Re: Antenna Height vs Gain

« on: August 09, 2018, 2042 UTC »

A few thoughts here;

Everyone's situation is different, but the same rules apply. If you have terrain shielding, nothing is going to get you to a receiver on the other side of a mountain....nothing outside of putting the transmitter on said mountain.

Without a clear understanding of the radiation pattern of the antenna your kinda shooting in the dark. I've had good luck with ring and stub antennas for CP over the years as they are light, fairly easy to construct, but a bastard to tune. Being somewhat horizontally polarized mutual coupling will change their VSWR response when coupled as an array.

If your primary audience is close in, use fewer bays and higher TX power. For more distant listeners, use more bays and lower power. You can play games with beam tilt by making one of the phasing lines longer than the other, but if terrain is your problem, nothing will fix that.

There is no magic antenna. All are a compromise suited for different situations.

For the record, helicals are impractical at FM frequencies. I was toying with the idea at one time, but to get any kind of gain at 100 MHz the thing had to be about 2' around and 20 feet long. I had better luck with a co-linear jpole with phasing loops.

As for modulation, either get one of the pira analyzers, or use and FM tuner with its baseband brought out to a peak responding meter, or a scope. Then compare your modulation to the other stations. DO NOT try and make yourself as loud as heavily processed FM stations, as most likely your processing is not capable of such density and you will wind up over deviating. The SDR trick is a good work around for you in the meantime. Also keep in mind that running subcarriers (RDS) will muttle your ability to discern a stations peak deviation. FCC rules allow stations to run over 100% modulation by 1/2 the deviation of the principle subcarrier in use. In other words, if a station is injecting 4% RDS, they are allowed to deviate at 102% peak modulation, or 76.5 KHz.

+-RH

626