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Messages - redhat

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166
The RF Workbench / Re: Someone had Corsair II AM TX experience?
« on: February 12, 2021, 1900 UTC »
I will be posting a YT video soon outlining a single device low parts count 4W transmitter driven by one of these class D amps.

+-RH

167
The RF Workbench / Re: Someone had Corsair II AM TX experience?
« on: February 11, 2021, 1023 UTC »
I've used this method with several different PA's over the last few years and have not noted any failures or issues.  Load impedance in my case was around 9 ohms, so no problem there.  Not sure what happened in your case.

+-RH

168
The RF Workbench / Re: Someone had Corsair II AM TX experience?
« on: February 11, 2021, 0215 UTC »
You could also replace the series modulator with a $11 class d audio amp board from amazon.  Efficiency would be MUCH higher, and it makes more sense to go this route since you already have a 24V supply at your disposal.

+-RH

169
General Radio Discussion / Re: HF Underground and Facebook?
« on: February 10, 2021, 0202 UTC »
Civilization on this planet has existed long before the aforementioned platforms.  It will also exist long after they are gone.

+-RH

170
Huh? / Re: WBCQ: Radio transmitter engineers wanted?
« on: February 02, 2021, 0335 UTC »
If I didn't already have a gig, I'd do this in a heartbeat.

+-RH

171
Huh? / Re: Why There’s More Music on AM Now?
« on: January 30, 2021, 1730 UTC »
Without looking to the article, this is mostly due to FM translators.  AM's are now a throw away broadcast property, as station owners assume that no one listens to them anymore, and talk doesn't make much sense on FM.

That's it in a nutshell.

+-RH

172
Probably better off with a 70' tower, which would provide a good match for 75 meters.  This would also provide some level of plausibility in case someone asks  ;)
BTW a 1/4 wave at the top of the AM dial just happens to be 5/8 on 4 MHz  :P

+-RH

173
That's cute  :D

+-RH

174
For a transmit relay, you can use an ordinary DPDT relay.  It would be wise to short the receiver output to ground during transmit.

+-RH

175
Making any sort of recommendation based on the current condition of frequency usage for an emergency is relatively pointless.  During such an event, band usage is going to be MUCH higher, and what is vacant today likely will be awash in various modes of data and voice.  This is also dependent on whether you are planning for near term, or in the future when propagation likely isn't known.  The best you could do is prearrange some 'calling' frequencies and times to try them, best spread over several band segments to allow for some variation in propagation, time of day, etc.  I would also include alternates located close by in case the channel you want to use is in use.

The simple solution to all these problems is ALE  ;D

+-RH

176
6924.990 KHz USB
2036 Kashmir, followed by George Thorogood. Clear reception with few shallow fades.
2047 sstv
2053 tone sweep, followed by "I'm done...are you there redhat?"  yes :)

Thanks for the show!

+-RH

177
Equipment / Re: Why 50 ohm coax cable?
« on: January 08, 2021, 1738 UTC »
The mismatch between 50 ohm and 75 ohm coax will create a SWR of 1.5/1.
Some hams will obsess over this in search of the perfect 1:1 match.
However, a SWR of 1.5/1 works out to a reflected power of only 4%.

See the ARRL Antenna Book Chapter 23, the section on Standing Waves,
they got a nice graph in there showing the how much power is reflected
for a given forward power and SWR.

The amount of radiated power wasted is not the primary concern when dealing with VSWR.  I will apologize ahead of time for derailing(at least temporarily) this thread  ;D
In the commercial world, best reliability comes with systems designed for low VWSR.  High VSWR is not only wasteful of TPO, but also causes hotspots in the line.  When you have perhaps 20% overhead on line capacity because the next size up is prohibitively expensive, low VSWR needs to be maintained to keep the line safe.  We are also in the era of solid state transmitters, which don't like VSWR.  Even commercial AM's will only operate at full power up to 1.5:1 before folding back.  Typically in commercial FM service, the antenna match at the output of the transmitter is under 1.1:1.  High VSWR in TV service causes problems with intermodulation  and spurious emission in the power amplifiers, so they tend to run lower, typically under 1.05:1 to maintain mask clearance.  The gear I build is designed with enough voltage rating to handle full power operation at up to 1.5:1.  We are on the bleeding edge of technology, and until we have transistors capable of 2KV or better Vds ratings, this will be the ceiling.

All of this, of course, is completely unrelated to receive antenna performance, where major shifts in impedance or standing wave will have little affect on the ability to receive a signal.

+-RH

178
Huh? / Re: Is It Time for Radio to Restore Dynamic Range?
« on: January 06, 2021, 1801 UTC »
Being on the inside, I have seen a lot of good things over the last decade of engineering.  One thing, bought music libraries are often lossless.  Hard disk space is now cheap enough that lossless makes sense.  Of course, if your playing pop, hip-hip, or a lot of similar genres that makes use of samples, what are you really getting with lossless?  Program paths are often PCM, particularly in larger markets.  Smaller markets are often running analog STL shots, so little has changed there.  Processing has gotten better too.  Most of the new flagship processors incorporate declippers, and all you have to do is wait for a Red Hot Chili Peppers song to come on and see if its being used  :P

I read something recently about the loudness war being over, as many online streaming entities are pushing the volume of hypercompressed content down, seemingly rewarding material with dynamics by playing them louder.  I hope the trend continues, and I have seen some indy stuff lately that looks less like a box on the waveform view of any DAW.  Unfortunately the music distribution system is moving farther and farther from a lossless world, and often the only version you can get of a song is MP3.  At least bandcamp would let you have a PCM version of a song if you wanted, but again there is no way to tell what the original source was.

As long as people are content to listening to music on the subway with tin can ears, the music industry will pump out content geared toward the lowest common denominator.

+-RH

179
General Radio Discussion / Re: FCC REPORT ON PIRATE RADIO ENFORCEMENT
« on: January 05, 2021, 2311 UTC »
I dunno, OFCOM has a pretty bad reputation as well.  Prison time for involvement in FM pirates?  At least we don't have that here...yet.

+-RH

180
Nice to see that finger pointing journalism hasn't gone out of style ::)

+-RH

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