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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 30th Jan 2020, 4:03 pm   #1
Malcolm T
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Default SSB crumby audio

I,m not sure if its my end or theirs but on 20 Mts some stations sound like daleks exchanging conversations , tha AM reception on the radio here is perfect and most other SSB as well .
The radio here is a HF225 vintage mid 80s.
I can only assume it has something to do with the fact the stations are using some form of SDR transmitting gear ie not good old analogue , its just terrible , like transmitting speech on a square wave !!
Am i correct , whats going on , I thought Amateur radio was about quality and care or is it some people just don,t care anymore ?.
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Old 30th Jan 2020, 5:51 pm   #2
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Default Re: SSB crumby audio

Could it be that, for some reason on 20 metres, the SSB is not Being resolved by the detector/bfo ?
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Old 30th Jan 2020, 6:28 pm   #3
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Default Re: SSB crumby audio

Do you have another receiver against which to compare it?

Is there a similar problem receiving SSB on 1.8 3.5 or 7MHz bands? Or is it just 14MHz-and-above?

Amateurs conventionally use USB above 10MHz and LSB below - which could suggest that if things are OK on the lower bands, perhaps the problem you're experiencing is with the USB carrier-insertion-oscillator. I'm not familiar with this particular receiver but does it use a switched pair of USB/LSB crystals in the CIO? Maybe your USB carrier-crystal is weak or has drifted off-frequency?

USB is the default for all military/civil-airband HF communications - do you still have issues when trying to receive any of the military VOLMET stations? Try listening for some of the VOLMET stations -

http://www.dxinfocentre.com/volmet.htm

to see if they're received OK. Gander on 13.270MHz would be a good one to try for.
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Old 30th Jan 2020, 7:11 pm   #4
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Default Re: SSB crumby audio

All the real tryers are found on 20m in the main. Excessive speech processing and over driven amplifiers will be to blame most likely.
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Old 30th Jan 2020, 7:21 pm   #5
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Default Re: SSB crumby audio

Quote:
Originally Posted by Jon_G4MDC View Post
All the real tryers are found on 20m in the main. Excessive speech processing and over driven amplifiers will be to blame most likely.
True: I've had a few 20M operators criticise my [Plessey VOGAD-battlefield-optimised Clansman PRC320] audio-quality, then be horribly surprised that I'm only running 30W PEP from a manpack radio.
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Old 30th Jan 2020, 7:42 pm   #6
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Default Re: SSB crumby audio

I think it's time to break out another radio as a check first .
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Old 31st Jan 2020, 12:41 am   #7
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Default Re: SSB crumby audio

Quote:
Originally Posted by G6Tanuki View Post
Amateurs conventionally use USB above 10MHz and LSB below
5MHz being the exception for which USB is the convention.

Kind regards
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Old 31st Jan 2020, 12:54 am   #8
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Default Re: SSB crumby audio

AmRad 20 m. has always been the DX-ers happy hunting ground. Hence, John's (G4MDC) post is probably right on the nail.

Al.
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Old 31st Jan 2020, 3:06 am   #9
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Default Re: SSB crumby audio

As Hams use LSB below 10MHz try for some commercial users on USB http://http://dxinfocentre.com/volmet.htm
ISTR that the 225 derives its CIO by programmable division of a XCO so is unlikely to be incorrectly set.
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Old 31st Jan 2020, 3:31 am   #10
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Default Re: SSB crumby audio

You can check whether it's a bad quality transmission by listening on one of the online SDR's.

For example:
http://websdr.ewi.utwente.nl:8901/
or:
http://hackgreensdr.org:8901/

There are various options to set received bandwidths etc and the demodulation (a software version of a phasing or IQ receiver) is of very good quality. Watching the waterfall display, a.k.a. frequency-time plot, gives a lot of information about received signals.

It's surprising how many terrible quality transmissions there are. I think many of them are due to overdriven or mis-adjusted "linear" amplifiers. There's also the problem of obscure adjustments, buried in the menus of the latest flashy toy boxes, that are so easy to set to silly values by mistake.

There was somebody on 80m the other morning who clearly had a broken linear. It was generating white noise about 20kHz wide in addition to, and 10dB stronger than, his rather distorted SSB. His contact eventually advised that there was something wrong, but in typical British fashion seemed reluctant to describe the severity of the problem...

And a strong CW signal on 3626.5 last weekend (readable on both of the above online SDR's) turned out to be the second harmonic of a contester, working stations on 1813.25.

Having said that, some HF broadcast stations no longer seem to have any monitors or maintenance staff and can go for weeks with hum, splatter, noise etc on their signals.
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Old 31st Jan 2020, 12:36 pm   #11
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Default Re: SSB crumby audio

Some SDR-generated sideband signals seem to have an almost bell-like resonance to them. It is as if the speech is being squirted out in a stream of amplitude/frequency droplets. Not sure what it looks like on a spectrum analyser but there does seem to be a distinct difference in quality when compared to the traditonal analogue-produced SSB signal.

These digitally-produced signals come from linears that are no doubt under the firm control of software inside the SDR driver, so the result should be 'clean' - but the audio is wierdly different to listen to.

But then, what would I know? (TS520S, TS830S plus three LG300s).

Peter (G3PIJ)
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Old 31st Jan 2020, 1:11 pm   #12
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Default Re: SSB crumby audio

Proper rigs Peter.
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Old 1st Feb 2020, 4:54 pm   #13
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Default Re: SSB crumby audio

Quote:
Originally Posted by m0cemdave View Post
Having said that, some HF broadcast stations no longer seem to have any monitors or maintenance staff and can go for weeks with hum, splatter, noise etc on their signals.
Its not just HF! Here in the US, we had a 100 kW ERP stereo FM station that
went for weeks with TWO simultaneous identical feeds into it .... separated
in time by 125 microseconds, equal levels. This was for both left and right channels.

What this did, of course, was generate a comb filter effect with a
50 dB dip at 4kHz and odd harmonics.

This sounds horrible, and also completely destroys stereo imaging.

It was not there on their simulcast "repeater" on the studio microwave tower
(the main transmitter is 23 miles away). That sounded fine (well, actually, if the input level of that one does not result in compression, I measure
the difference signal between it playing a CD and the CD itself, time and phase corrected, cut off at 14.5 kHz, at about 50 dB, which is superb) . Its mostly a classical music station.

It took numerous calls to them to even get them to get me to "engineering".
The people manning the desks (its a University AM-FM-TV station that is a very real station doing their own programming, been around for 100 years!)
claimed that no one ever monitored the programming. Engineering had a difficult time understanding what I was explaining. I eventually sent them an
FFT of program material clearly showing the dips. The junior engineer (only) finally instantly understood (he remembered what a comb filter does from class). It took him ten days to find the problem.

I still wonder why a station never listens to its own programming!
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Old 1st Feb 2020, 10:13 pm   #14
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Default Re: SSB crumby audio

Hi Malcolm,


I have a Lowe HF225 here and it works fine on SSB. Transmissions probably over processed to start with and then massively overdriving linear amp. A good reason to stay on AM!
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Old 5th Feb 2020, 3:34 pm   #15
Malcolm T
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Default Re: SSB crumby audio

I've found the problem! The radio was sitting directly on top a Yaesu FP 8 power supply, groan.
Picking up interference from the transformer windings no doubt, radio has now been re-located.
Appreciate all your suggestions, I was just having one of those no think days.
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