RF Based Speech Processor for SSB use

Hi all,

Hope you're all keeping well and enjoying your radio.


I have a question to ask. Have or do any of you utilise an RF speech processor?


I'm not talking about 'power mics', desk mics or other means of pre-amplification that allows me to hear your dog farting in the background on your QSO .....


...we're talking about those units that convert your audio into RF for processing before converting back to audio to avoid distortions from said processing.

Think old school Datong units or Daiwas, maybe even the more modern Ten-Tec Model 715.

I've seen some great designs for such units from the likes of YD1JJJ, PA0FRI and even in an old copy of Practical Wireless. (PW March 1986 to be precise - er yeah, my wife does think I'm a hoarder! )
From the technical specifications and descriptions it would seem such an item would be worth building but I'd rather have some personal opinions on usage of such items rather than pure technicalities.


Do any of you use such a device?
Have you used such a device in the past and what where your thoughts on it?
Do they work as well as specified giving a much needed boost to your SSB signal?



Any input would be most appreciated.....

....so long as it's less than 5,000 words and doesn't encompass the existential existence or vagaries of radio communications to tier...blah-de-blah-blah.


Oh, and I'll definitely give a big 'thanks' and 'like' for any useful information.  

Look forward to hearing from you.


All the best,
Victor

Nope, though I do have the speech compressor in the iCom turned on, to do much the same job with boosting the overall "level" of the SSB signal....but I run very little mic gain as a result too.

Cheers Jeff.

Just trying to find out as much as I can. Looks good on paper, but if it's so good....why isn't everyone using one?

Did figure out some issues between electret capsules that pick up every damn thing when amplified compared to dynamic mic setups, (all my Yaesu's are dynamic). Reviews on such items are scant and sometimes perplexing with individuals moaning they don't work well on FM.....Really?!?


Just on a quest with my recent FT290 acquisition - really impressed with the range especially VHF SSB and with it's QRP 2.5W O/P. Rather than bolting on 'linears' just thinking about processing to maybe enhance that range.


Much appreciated.

Everyone on CB uses power mics and they're of no use on UKFM.

People using ham gear will just turn on the compression.

I use it on my Icom Victor, used it on my Yaesu too...  just kept to the manuals setup instructions, and all seems to work just fine.

Cheers Jeff, (53Prefect).


So far no one has really given me an answer to the actual question I posed so perhaps I hadn't explained myself well enough.

Even my old FT757 has a SSB processor on it, albeit with no real settings but just a press of the button. It barely makes a difference though in reality obviously fairly limited to prevent audio distortions. It utilises a simple diode clipping audio compression method so I'm not at all surprised.

Modern radios use different compression chip methods and even DSP, (Digital Signal Processing), to boost the audio for SSB usually in the audio chain and again fairly limited. There are exceptions that do their best to process along the TX RF chain but once again in a limited form. Other examples play some jiggery-pokery methods on the RF outputs.

I know that these methods can produce some difference to your signal but not quite as good as expected or achievable.


As mentioned I am looking for a method to boost my VHF SSB on my FT290r and it doesn't have any form of compressor whatsoever. I can't simply press a button or make a menu setting change.


The method I am looking at and the units I mentioned utilise an RF method to process the audio signal. 

An audio signal when processed heavily will create distortions along the audio harmonic chain which usually shows up in the final radio signal with IMD, (Inter-Modulation Distortion), artifacts causing typical signal 'splatter'. I think this is why people avoid such methods or keep it fairly limited.

The RF method first converts your microphone audio signal to a low frequency RF, (normally 455KHz but sometimes in the MHz region), usually a DSB, (Double Side Band), signal which is then processed and filtered before being converted back to an audio signal. The idea is that any harmonic distortion occurs in the RF region and so of no consequence being filtered out when converted back to an audio signal. It is then this signal that is passed onto the radios microphone input.

All clever stuff and such units can be built small enough to fit inside a fist mic.

It all looks good on paper but I've yet to come across any examples of personal use of such items, (used correctly and not trying to boost an FM signal where such things are useless!) There should be much more boost to the signal than achievable by other methods.


I can see why manufacturers simply don't bother as most products are 'bean counted' to the N'th degree. It's usually mentioned as a method to 'keep prices low for you' guff when I know it's about final profits. (Why else would manufacturers put 16 volt rated capacitors in a radio designed to run off 13.8 volts when most electronic engineers know to 'double rate' and recommend at least 25 volts for surge current and supply ripple/variation? Maybe that's the re-capping myth issue right there! )

There's also historical arguments along the typical them & us, CB vs Ham nonsense. Speech processors & power mics were often used incorrectly by FM CB users where they served no real purpose other than a perceived performance increase. Most designs offered to Hams were the limited audio path method and often not well understood.


Perhaps Datong, Daiwa & Ten-Tec were onto something but people simply didn't 'buy' into it.

Looks like I may have to look into it more myself. I had hoped someone here had personal experience.


Thanks to all anyway.

All the best,
Victor

All over my head Victor i wish i could help.
My ft991a must have loads of settings but i only turn the mic gain up and that is it.
Surprised our friend hasn't sorted you out but time yet lol.
I have every faith in you m8 you will sort it out.

Ha!

No worries Alan mate. Looks like I'll have to build one and find out for myself.  


I had hoped I could find out more 'user experience' thoughts this often being better than straight technical specs.

I used the Datong RF compressor for a number years on my TS790E.

Doing tests with other hams it did have an quite an advantage over no compressor
and it gave a cleaner signal as long as it was kept within the ALC zone.

In fact I still have the beast in here some where.

That's absolutely pure gold Mike!   

A first hand personal perspective of such units and their effect on operation is exactly what I was after.

Looks like it's an avenue worth exploring more then and I appreciate your user experience input.
(Often worth way more than 'on paper' specs. )


As promised in my original posting, 'Thanked' & 'Liked'. Much appreciated.

I have a crap voice for SSB it never really peaks the tx like other ops.

There was a review of the Datong in RADCOM and I bought one to experiment.

Around here most of the hams on VHF were very big stations and chasing DX I just couldn't break through them, not even running 200watts.
When I got the Datong going the DX often heard me first, not all the time but often busted pileups.
The trick is don't be fooled in winding up compression to much, the Datong would go to 30db but 6db to 12db was enough to keep the ALC happy and the signal would be clean and loud at the other end.
Follow the rig makers recommendation on the ALC setting and you should not get bad reports.

Cheers for the extra info Mike, again much appreciated.

The unit I'm looking at building performs a moderate compression of 6 - 12db so should all be good.

Hi again,

A bit of a resurrection on this thread but thought I'd add an update as to how I've progressed in case it's of any interest to anyone.


Spent some time looking at different RF based speech processors and noticed the common idea to them all :-

Mic ---> Mic Preamp ---> RF Double Sideband Modulator ---> Diode clipping ---> RF filter ---> Sideband Demodulator

Which then outputs the compressed audio signal minus the audio harmonics thanks to the RF processing.


Hmm....Seems I have half that stuff already going on inside the FT290!

Mic ---> Mic Preamp ---> RF Double Sideband Modulator  ---> RF filter ---> etc.

Surely I can just add the clipping diodes inside the radio between the DSB modulator and the Sideband RF filter?


After some digging around it seems that this is exactly the way the old Yaesu FT107 performs it and akin to the SSB processing on the old FT101 series too. Now we're getting somewhere!


So after comparing the circuit diagrams of the FT107 and FT290 it seems I have found the place where I can add the clipping diodes to my FT290 giving me built in RF speech processing. A quick measure of the voltages shows that I have some 1.4 volt of signal going on so well within the range of a couple of diodes like the ubiquitous 1N4148's. As the mic gain for the SSB and FM sides is independently handled, (separate trimmers), I should be able to fit this internal to the radio so not upsetting the FM side of things.

A quick look at the circuits below to show what I'm on about :-




A bit messy I know but it's often hard to get good scans of old circuit diagrams.

On the left is the FET buffer for the DSB audio signal in the FT290, on the right is the BJT buffer and back-to-back clipping diodes, (D15, D16), on the FT107. I should simply be able to fit the diodes and DC isolation capacitor, (probably choose a lower value than on the FT107 though), to the FET buffer on the FT290 and perform the same job.

Awesome!  

I may keep the level of compression lower than anticipated but should be able to accommodate some 6dB or more without degradation. Not to be sniffed at.

If the levels appear too high in an external environment, wind noise etc. (this is a famously portable rig after all), I should be able to reduce my audio level via a microphone mod. I have the original YM-47 mic with this radio which has the 'Lock' switch on the back to which I can rewire with the aid of a resistor and switch the mic level to 'high' and 'low' levels accordingly.


Anyway, I'll let you know how it all goes but thought I'd share it as it's a 'mod' I haven't come across in the usual resources. (Most seem to be interested in 'frequency expansion'!?!?!)


I know it might be as Alan, (Alan Pilot), put it "over my head" for some, but you never know.....there might be someone as idiotic as me with a soldering wishing to delve into their pride and joy old radio. In which case this might just be invaluable.


Best thing of all, a bit of thought means I don't have to acquire or build a whole RF speech processor......just add two cheap diodes, a capacitor and not burn my fingers on the soldering iron during the process.


Thanks again for putting up with my 'waffle'.

All the best,
Victor

Keep at it Victor you can do it.

Thanks for the vote of confidence there Alan.  

The brain still works so now it's just down to the bear paw hands and bat like eyes!

(Lack of test gear is still a hindrance - why do people want so much dosh for 40 year old oscilloscopes?!?!)

Victor
Covid doubled the price of all second hand radio/gear.
Have you looked at the prices on the bay.

I did Alan mate. 

DSO's are way cheaper than they used to be with good specs but I had hoped that'd have a knock on effect on second hand CRT units. Fat chance! 

We're at that technological switch over point now....heck it's cheaper to by a brand new SDR based transceiver than an old boat anchor nowadays. (Looking at that stuff now after the 'Xiegu G90' thread. )

Thing is, can't repair the modern stuff but can still flip a transistor or valve and love those big old dials & knobs!

Well after digging out my best +3.0 dioptre reading specs I got the job done!


The old bear paw hands managed to twist together a pair of 1N4148 diodes back to back, joined to a 1nF capacitor and whilst tentatively held with the smallest needle nose pliers you ever did see, soldered onto the radios printed circuit board.

I had to remove the old battery bay to access the rear of the circuit board and then utilised a powerful LED lamp to shine through the board on the component side so I could trace the PCB track paths required. A couple of quick dots marked with a suitable pen allowed me to see where I had to solder the components in place.


Now I don't have a lot of test gear but more than some so pushed ahead with what I have to adjust this modification up.

A quick adjustment of the SSB mic preamp trimmer pot saw the internal power meter bounce around on long spoken "Ahhh's" and "Fiiive's" from the '5' to '6' mark to around '9' and a check on a homemade RF power meter, (50 ohm dummy load, rectifier and calibrated meter), showed I had jumped up from an average of around 2 watts to some 3 watts.

Wow, QRP levels are amazingly low but that was a massive jump in all reality!

With the aid of a homemade RF tap and digging through stuff, (my junk box), to find a Germanium diode I made a simple demodulator/station monitor to check the audio signal on the RF output. This is handy as my old Telequipment oscilloscope starts dropping off or attenuating around 3.5MHz and bottoms out around 5 MHz so not really any good to see a 144MHz signal(!) This simple 'trick' allows me to see just the detected audio so well within the range of my ancient oscilloscope.

The signals seen showed a good full range whilst transmitting and speaking into the mic without any massive distortions or clipping so all good. A quick check with a simple wave meter, (anyone old enough to remember them?), showed no issues with RF harmonics caused by Inter-Modulation Distortion, (IMD).

None of what I've done so far shows me an 'accurate' measurement, (numbers, numbers, fap, fap!), but good enough to show I'm on the right track with no discernable problems.


The real test would be an on air transmission and luckily I have a very good Ham friend, (Hiya Gary!), with whom I speak to regularly on 2m as he travels around in his work van. 

His instant report when switching to SSB was how much clearer my audio was compared to previously made transmissions with him. Apparently I was a lot 'clearer' with the audio signal being 'crisper' as apparently I had a slight 'muddy' and almost too 'bassy' signal before in comparison. Now I know that this is all subjective but will do me nicely and I trust his feedback than some random operator on air who cannot make a comparison due to no past/previous contact.

The real test came about as he did his usual travel home across my county into the next where he lives. Seems that even as my signal faded in S-meter terms my audio was still punching through a radio 4 to 5........Fantastic!   


Looks like I've made a good enough job of 'improving' this 40 year old radio and having inbuilt RF speech processing pleases me no end. I did a check with an FT8 digital transmission too ensuring that no problems occurred there due to this boost. All looking good too.


----------------------------------------------------------------------------------------------------------------------------------------------

Boring for some I know, but a real 'Ham' radio triumph for me of keeping that old soldering iron hot, an aspect of Amateur Radio that I have always appreciated and loved no end. As a still 'new' Amateur myself I was chuffed to accomplish such a thing.

Thing is, I could replace most of this homemade test gear with a simple SDR receiver and performed most of the checks.
(How many check their amateur stations with regard to the licensing terms & conditions? )

But I don't have one......so made do with what I've got.


A big thanks to Koenraad who originally donated me the FT290r and also to my dear friend Gary for his invaluable help.

Thanks to you also if you read through my usual 'waffle'. 


All the best,
Victor

I said you could do it Victor.
I have more faith in you than i have in myself.
(A lot better today).

Morning Alan,

We are as they say are our own worst critic.
(I didn't think I'd be able to suss this stuff out let alone accomplish it!)

Glad to hear you are feeling better mate.  

Keep well.

Hi Victor

Really interested in this mod, as I have an FT290R (also a 690R) that I'd be interested in doing the mod to...do you remember/have images of the location for the diodes and cap on the underside of the pcb? I have (probably) worse fine motor skills than you, so any help would be appreciated.

I doubt we could QSO on 2m SSB with 2.5W but you never know...6m might be an option though!

73

Mark, G8XQB

Hi Mark,

Good to hear of someone with the complete line up of these old radios, great stuff.  

I've had a dig around my hard drive looking for the images but can't seem to find it at the mo. Leave it with me and I'll pop the radio apart to take another picture and post it up here for you.

It was a fiddly job but I do remember wiring up the diodes to a larger bodied cap to make it more handleable.



You never know, with a bit of tropo lift we could bag a 2m SSB contact but ashamedly I've not done much 2m SSB after discovering what a barren desert of activity it is. Unfortunately I don't have 6m capabilities but you've got me thinking on about rectifying that!


All the best for now,
Victor

Hi again Mark,

Took a quick picture and you'll have to forgive the quality but best I could do on my old iPhone 6.
(I have a DSLR camera with macro lens somewhere but damned if I can find it!)





I had used quite a big capacitor (physical size wise rather than value) and soldered the diodes to that before inserting the whole thing on the PCB then flattening the capacitor down to clear the battery box. Was far less fiddly than the tiny 1nF cap I had tried previously!

You'll have to adjust your SSB modulation drive via VR1001 the 22K pot that sits between Q2001 and Q2002 to achieve final results. You can kick it up a fair bit before clipping distortion becomes too much. YRMV.


Anyway, hope that helps.

All the best,
Victor



Disclaimer:-

I don't usually respond to such requests from new members on the forum in an effort to keep the community minded spirit alive on Charlie Tango with sharing being a two way street. Also there's the issue with some blaming you for them mucking up their radios with such 'mods'. (I can't help your lack of soldering or electronic skills! )

However in this instance it was a polite request from a fellow Ham and in the true Amateur Radio spirit was more than happy to offer any assistance I could.

Thank you for that Victor - much appreciated, and very helpful.

Did you ultimately switch the mod in and out using the mic switch, or leave as was? Curious, as obviously using speech compression on FM is ...awful! In my case it won't really matter as I will only be using the 290 on SSB.

I have dug the 290 out of storage and will be performing the 'surgery' (hopefully) this coming weekend. Whether I can find anyone to talk to on 2M is a different issue however! I also plan to take a look at the circuit of the FT690 to see if a similar mod can be performed, as that may have more mileage...

Thank you again for taking the time to post your reply and the picture - it is very much appreciated.

73

Mark, G8XQB