796
The RF Workbench / Re: Zener diode testing?
« on: October 20, 2017, 0457 UTC »
In that case, those wafer switches should be fine. Mouser and digikey should have other options as well.
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Shortwave Pirate Radio In North America And Around The World, And Other Signals That Go Bump In The Night
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.
Many of the larger markets have 'franken FM's' which are low power stations on channel 6 intending to broadcast on FM. Operating on channel 6's aural is not possible in such areas.
In larger markets, a low power AM makes more sense than FM, simply because there is usually more available spectrum, especially during the day. With the advent of HD translators, FM spectrum in ALL markets is becoming extremely scarce.
+-RH
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797
The RF Workbench / Re: Zener diode testing?
« on: October 20, 2017, 0114 UTC »
It looks like the switch does more than those three metering position. Front panel shows off-standby-volts-current-relative output.....that's 5 positions and judging from the schematic at least a three deck switch.
More research needed.
+-RH
More research needed.
+-RH
798
FM Free Radio / Re: Legality of broadcating on 87.9 MHz
« on: October 19, 2017, 0113 UTC »
The letter of the law is left open to interpretation and as usual quite vague. This is usually done to allow inspectors greater lattitude in the field. Under the intentional radiator category, the law states 100uV/M below 88 MHz, but 150uV/M above.
https://www.law.cornell.edu/cfr/text/47/15.209
Yet in this part, its states 250uV/M
https://www.law.cornell.edu/cfr/text/47/15.239
Who knows....
+-RH
https://www.law.cornell.edu/cfr/text/47/15.209
Yet in this part, its states 250uV/M
https://www.law.cornell.edu/cfr/text/47/15.239
Who knows....
+-RH
799
General Radio Discussion / Re: Shortwave Station Bends But Doesn’t Break
« on: October 14, 2017, 1944 UTC »
Usually with towers that far gone, the only recourse is controlled demolition. Even once a tower is on the ground, it can still be dangerous because sections of it are under spring tension.
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800
The RF Workbench / Re: Zener diode testing?
« on: October 14, 2017, 0022 UTC »
Sounds normal. Best way is with an adjustable bench supply and a suitable dropping resistor, maybe 10K. Ramp up the supply while monitoring the voltage across the diode. It should keep rising until you reach its breakdown voltage, then stay there as input voltage is increased.
Keep in mind if the diode is backwards, it will function as an ordinary diode with a 0.5~0.7V forward drop. You can verify this with your DMM on diode check.
+-RH
Keep in mind if the diode is backwards, it will function as an ordinary diode with a 0.5~0.7V forward drop. You can verify this with your DMM on diode check.
+-RH
801
General Radio Discussion / Re: X-FM is headed for dry dock
« on: October 11, 2017, 2158 UTC »
Not at this time. I may in the future as we move to more built-in-house gear. Feel free to send me a message if you or any other ops need engineering help.
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802
For Sale / Wanted / Barter / Re: T-368
« on: October 10, 2017, 1820 UTC »
Yup and something of that power now could fit in a Pelican case...a big one, but still.
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803
General Radio Discussion / Re: We're doing it this time.
« on: October 05, 2017, 0424 UTC »
Just an FYI, the trenchcoat fella logo on the Wiki page is missing...some stock image is in its place...
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804
General Radio Discussion / Re: "Preacher Teacher" Alert
« on: September 28, 2017, 0143 UTC »
Lunatic fringe
I know you're out there
You're in hiding
And you hold your meetings
I can hear you coming
I know what you're after
We're wise to you this time (wise to you this time)
We won't let you kill the laughter....
+-RH
I know you're out there
You're in hiding
And you hold your meetings
I can hear you coming
I know what you're after
We're wise to you this time (wise to you this time)
We won't let you kill the laughter....
+-RH
805
The RF Workbench / Re: About Vpp, Vp, Vrms and P(R) [solved]
« on: September 27, 2017, 0010 UTC »
That's one of the reasons I always leave my probes in 10x. Check your tilt correction on the probes as well and make sure that is set correctly, or you will get excessive error.
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806
General Radio Discussion / Re: "Preacher Teacher" Alert
« on: September 26, 2017, 1142 UTC »
It's a free country, and shortwave stations are struggling to stay afloat. He buys airtime on these stations.
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807
The RF Workbench / Re: About Vpp, Vp, Vrms and P(R)
« on: September 26, 2017, 0232 UTC »
The formula I always use is.... W=(0.707 ( Vpp / 2 )^2 / Zload
For example, I have a transmitter producing 636V peak to peak...
Divide by 2 = 318V
Times SQRT of 2 (0.707) ~ 224.8Vrms
Squared .... 50546.73
Finally, divided by your load impedance,
1,010.9W
This formula only works with relatively pure, steady state signals. Those with lots of harmonic energy can screw up the measurements, as can a reactive load. One thing that bites me sometimes is forgetting that my Bird termination/wattmeter combo begins to roll off at 30 MHz, so anything below that is uncharted territory. Case and point, I was repairing a commercial broadcast transmitter with it on ~800 KHz and the bird said around 150W. The forward power meter on the transmitter said 1,000W, which was confirmed by my fingers on the end of the load and also a scope making voltage measurements.
On a similar note, if your scope is set up wrong, or the probes have a problem, your accuracy will suffer.
+-RH
For example, I have a transmitter producing 636V peak to peak...
Divide by 2 = 318V
Times SQRT of 2 (0.707) ~ 224.8Vrms
Squared .... 50546.73
Finally, divided by your load impedance,
1,010.9W
This formula only works with relatively pure, steady state signals. Those with lots of harmonic energy can screw up the measurements, as can a reactive load. One thing that bites me sometimes is forgetting that my Bird termination/wattmeter combo begins to roll off at 30 MHz, so anything below that is uncharted territory. Case and point, I was repairing a commercial broadcast transmitter with it on ~800 KHz and the bird said around 150W. The forward power meter on the transmitter said 1,000W, which was confirmed by my fingers on the end of the load and also a scope making voltage measurements.
On a similar note, if your scope is set up wrong, or the probes have a problem, your accuracy will suffer.
+-RH
808
FM Free Radio / Re: Any stations in Los Angeles?
« on: September 23, 2017, 2130 UTC »You can't blame the Hobbyist for wanting to broadcast a mile or two and since Channel 6 no longer uses 87.75 Mhz befcause its Digital now and has moved into the UHF band the FCC should indeed allow 87.7 Mhz to be a sort of Public Access Channel where especially in Rural Areas your allowed 5-15 Watts.
Many of the larger markets have 'franken FM's' which are low power stations on channel 6 intending to broadcast on FM. Operating on channel 6's aural is not possible in such areas.
In larger markets, a low power AM makes more sense than FM, simply because there is usually more available spectrum, especially during the day. With the advent of HD translators, FM spectrum in ALL markets is becoming extremely scarce.
+-RH
809
General Radio Discussion / Re: ISO someone to relay a radio theatre show
« on: September 23, 2017, 2115 UTC »
Perhaps the best way to accomplish this is post a link to your show on internet archive or similar and from there someone can pick it up to relay.
+-RH
+-RH
810
The RF Workbench / GPS discipline a cheap Ebay DDS module
« on: September 23, 2017, 2107 UTC »
A neat idea I came across today. Instead of disciplining the reference oscillator, just measure its drift and update the DDS frequency! Generate any frequency from 10Hz-30MHz with precision of better than 1 Hz.
Uses (mostly) off the shelf hardware. You do have to build a divide by 32 prescaler for the DDS clock.
PDF http://www.knology.net/~gmarcus/VFO/GPS_Sig_Gen_v1_1.pdf
Arduino code http://www.knology.net/~gmarcus/VFO/AD9850_gps_vfo_v1.ino
+-RH
Uses (mostly) off the shelf hardware. You do have to build a divide by 32 prescaler for the DDS clock.
PDF http://www.knology.net/~gmarcus/VFO/GPS_Sig_Gen_v1_1.pdf
Arduino code http://www.knology.net/~gmarcus/VFO/AD9850_gps_vfo_v1.ino
+-RH
