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HF/MW/LW Equipment - For general and technical discussion of all receivers which cover the HF bands. For HF tranceiver discussion please use the Amateur Radio Equipment forum above.

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Old 03-13-2017, 11:42 AM
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Unhappy HF radios with working squelch

Does anyone know if it's only the Alinco R83E and Icom radio HF sets that has working squelch ?
or if any portable HF sets have working squelch?
Has devastated my loop antenna is knakererd for the time being because the interface isn't working!.
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Old 03-13-2017, 3:17 PM
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AGC derived squelch on HF is not very successful, especially on utility stations where it would actually be most beneficial. This is because the squelch is usually driven from the same circuit that drives the "S" meter which is derived from the AGC - the measure of the strength of the signal. If there is plenty of signal, then fine, the squelch will often work quite well as you can back it off sufficiently to kill the noise. SSB stations don't have a carrier to drive the "S" meter so there's nothing to lift the squelch until someone speaks and often the first syllable is missed.

But there's the problem - in a VHF radio most of the noise comes from within the radio itself plus just a bit of cosmic noise so it is relatively constant and the voice signal many more times larger than the noise. But on HF most of the noise is atmospheric, static crashes and bangs, interfering signals etc often much higher in level than the required signal so the squelch will open on the signal you don't want and ignore the ones that you do!

The best solution is a radio with an RF gain control which you can back off so as to reduce the noise but still hear the voice.

Second choice would be a (expensive!) radio that has audio-derived squelch - it listens for speech frequencies and patterns, analyses them in a bit of software and then sends them to the speaker if they comply with the algorithm - often with a bit of a delay where the signal is stored while the analysis is going on.

...and of course you mustn't ignore the MK1 earhole - it's very good at ignoring background noise and picking up a voice or morse code buried underneath! My old Kenwood R2000 has a squelch control and I fitted a mod to give it an RF gain control - guess which one I use for the HF aero that I listen to most?
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Old 03-13-2017, 7:32 PM
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The audio derived squelch you mention is commonly called "syllabic squelch" and its the best thing going since Marconi got his first radio working. Depending on the mfr, it uses two or three sharp audio filters, one in the lower human voice range, one at several KHz where your radio hiss noise is and sometimes another within the voice range.

It filters these two or three audio ranges, detects the noise then feeds a switch for each that changes with the presence or absence of sound at each frequency. Then its fed to some logic where the presence of all is ignored but if there is human voice range audio present and lack of high frequency hiss noise, then the squelch opens. This type of squelch ignores carriers, most interference and works very well with weak signal SSB voice.

I have a couple of radios with it built in and they are a joy to use. You can buy syllabic squelch circuits to install into most any radio. Here is one that is a bit pricey but I have one in kit form that was very inexpensive and I'll try and track down where it came from. This would allow the OP to use any radio he wants and have the best squelch possible. VOS-1 VOICE OPERATED SQUELCH for SSB Single Sideband Radio from Naval Electronics
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Originally Posted by majoco View Post
AGC derived squelch on HF is not very successful, especially on utility stations where it would actually be most beneficial. This is because the squelch is usually driven from the same circuit that drives the "S" meter which is derived from the AGC - the measure of the strength of the signal. If there is plenty of signal, then fine, the squelch will often work quite well as you can back it off sufficiently to kill the noise. SSB stations don't have a carrier to drive the "S" meter so there's nothing to lift the squelch until someone speaks and often the first syllable is missed.

But there's the problem - in a VHF radio most of the noise comes from within the radio itself plus just a bit of cosmic noise so it is relatively constant and the voice signal many more times larger than the noise. But on HF most of the noise is atmospheric, static crashes and bangs, interfering signals etc often much higher in level than the required signal so the squelch will open on the signal you don't want and ignore the ones that you do!

The best solution is a radio with an RF gain control which you can back off so as to reduce the noise but still hear the voice.

Second choice would be a (expensive!) radio that has audio-derived squelch - it listens for speech frequencies and patterns, analyses them in a bit of software and then sends them to the speaker if they comply with the algorithm - often with a bit of a delay where the signal is stored while the analysis is going on.

...and of course you mustn't ignore the MK1 earhole - it's very good at ignoring background noise and picking up a voice or morse code buried underneath! My old Kenwood R2000 has a squelch control and I fitted a mod to give it an RF gain control - guess which one I use for the HF aero that I listen to most?
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Old 03-13-2017, 9:04 PM
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Syllabic Squelch was introduced by Motorola in the original Micom HF-SSB series in the mid 70's'. I installed and maintained a network of Micoms in West Africa in the 1977-1980 timeframe. Now that Motorola sold that part of their business the current radios are marketed under Mobat. The Mobat 3T ALE radio setting on my desk came with a Motorola mic.
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Old 03-13-2017, 9:29 PM
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If your still interested in other HF radios with a squelch, you can add the FT-1000, it's brother the FT1000 MP, the FT-2000 and the FT-5000 MARK V for starters.
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Old 03-13-2017, 9:37 PM
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Syllabic squelch was sold in radios long before the Micoms were made. I had a military HF manpack designed in the late 60s that had syllabic squelch and it worked better than some of the latest versions I've tried.

I believe the OP is looking for portable type HF receivers, not transceivers, that's why I mentioned the user installed squelch boards.
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Originally Posted by rfradioconsult View Post
Syllabic Squelch was introduced by Motorola in the original Micom HF-SSB series in the mid 70's'. I installed and maintained a network of Micoms in West Africa in the 1977-1980 timeframe. Now that Motorola sold that part of their business the current radios are marketed under Mobat. The Mobat 3T ALE radio setting on my desk came with a Motorola mic.
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Old 03-13-2017, 10:11 PM
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Actually it was codan who started it. Carrier Operated Device Anti Noise. Or so I've read.
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Old 03-13-2017, 10:36 PM
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I never knew that and just found this posted from a VK5ZEA "A HF SSB squelch/mute that operated on voice has been a feature on Codan HF equipment for a long long time. The name Codan is an acronym, Carrier Operated Device Anti-Noise... a reference to the mute circuit they developed in the 1960's that kept their HF radios quiet unless someone was actually talking."
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Actually it was codan who started it. Carrier Operated Device Anti Noise. Or so I've read.
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Old 03-14-2017, 3:17 PM
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Interesting. The Codan 6801 service manual, complete with PC board layout is available here...

http://www.radiomanual.info/schemi/S...01MK2_serv.pdf

The LM3900 IC is still cheaply available.
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Old 03-14-2017, 3:27 PM
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The larger circuit board in the link from post #3 looks nearly identical to the kit I built and I think it cost me around $25, including the board and all the parts. I just don't remember where I bought it.
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Originally Posted by majoco View Post
Interesting. The Codan 6801 service manual, complete with PC board layout is available here...

http://www.radiomanual.info/schemi/S...01MK2_serv.pdf

The LM3900 IC is still cheaply available.
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Old 03-14-2017, 3:31 PM
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Ah, you mean this one...

VOS (Voice Operated Squelch) Audio Muting Kit Form | eBay

Can$55.
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Old 03-14-2017, 3:39 PM
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Yes, that's it. But I didn't or would not have paid that much for it. Otherwise it works well, not as good as the ones built into my radios, but a lot better than any regular squelch.
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Old 03-14-2017, 5:09 PM
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I'm wondering how difficult it would be to use a small microcontroller to do this? Perhaps sample the raw audio using one of the analog inputs, store the values over a certain period and then do a comparison. If energy is detected within certain frequency ranges enable an I/O pin to operate the audio gate.
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Old 03-14-2017, 6:21 PM
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You would still need to filter at least two different and narrow bands of audio and detect them to feed to the micro, and I think that's a bit overkill since a simple switch and gate circuits have been used in the past. Unless the microcontroller has the ability to sample specific audio frequencies on its own.

Then there is the potential delay problem, you want this squelch circuit to act immediately so no information is lost. One way around that is to delay the audio path by at least as much as the detecting and switching process.
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Originally Posted by mancow View Post
I'm wondering how difficult it would be to use a small microcontroller to do this? Perhaps sample the raw audio using one of the analog inputs, store the values over a certain period and then do a comparison. If energy is detected within certain frequency ranges enable an I/O pin to operate the audio gate.
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Old 03-14-2017, 7:26 PM
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I have used freqMeasure with the Teensy board in the past to detect CTCSS. It returns a Hz value in a variable called frequency.

Maybe something like:

if (frequency >= 500.00 && frequency <= 3000.00){
voiceDetect = true;
}

That would detect but would not account for constant carriers within the pass band. So then maybe gather several true false results and store them.

After X number of results are gathered continuously compare them. If that defined X number of results return false more than 2.5 times a second then close squelch.

Something along that line. Maybe not exactly that but comparison of samples against a value within a certain time period to set the determining factor.

The board is fast enough to gather plenty of samples in time to work with it.

I'll try to set up the SDR on HF with non filtered audio output to simulate the discriminator/detector audio in a radio and feed it to the Teensy.
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Old 03-14-2017, 10:09 PM
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While this algorithm...

if (frequency >= 500.00 && frequency <= 3000.00){
voiceDetect = true;

will detect a voice within that passband, unfortunately lots of whistles, monkey chatter, static crashes also will tick the 'true' box.

The Codan board has two filters with passbands of 2.0 to 2.7kHz and the other 590Hz to 1040Hz and there has to be a signal in both channels for the squelch to open. They've obviously done some research into the characteristics of lightning crashes in the Aussie outback because I would have thought there would be some energy in both those passbands. Perhaps I feel an experiment coming on....
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Last edited by majoco; 03-14-2017 at 10:35 PM..
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Old 03-14-2017, 10:51 PM
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I see that they have a new freqcounter library that will simultaneously count several inputs with the newer Teensy boards. What if a guy set up the hardware filters as you mentioned then fed each to a separate input. If both are satisfied then open, else close.

Also, I think the timing is what is accounting for the lightning as you mentioned. The documentation I've found mentions that the signals must vary at a rate of .5 to 3.25 Hz to be valid. So, a single crash would not satisfy that requirement.

I'm messing with the regular counter right now trying to get it to interface to the PC. It will pick up the 60 hz ambient noise if I put my finger on that pin/lead but I think I need a higher audio output to drive it than this headphone output port. When I connect it to the headphone output it stops counting.

I think I'm going to give that multicounter library a try and get it working detecting two channels then try to go from there.
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