Ham International Concorde 3 bad audio on SSB

[lbcomms]

Either one of two things, an earlier stage (predriver or driver) has gone low gain and has to be overdriven to get close to 12W out of it, or one of the components in the output filter area (L10 to L13 and the associated ceramic capacitors) has died. When you adjust the SSB audio drive level to halfway, what sort of output power do you get for how much DC input current?

If it's 3 to 5W and only drawing an amp, then the predriver or driver is most likely the cause, but if its 3A+ for a couple of watts then it's most likely the output stage.

Do you have an oscilloscope (preferably an analog one capable of at least 20 MHz) and a 10X probe for it? If you can see what's happening it's a bit easier / quicker to find these sort of faults...

[ballo]

I have a scope 60 Mhz with a x10 probe .
At the VCO mixer on TP1 i see a good waveform on the scope

I turned the compressor off and i got a worser audio , compressor on delivers the best audio.

When i turn the pot VR9 to 50 % , the Concorde draws 1,9 A with the power on max.

In the attachment i took a picture measured on the famous R41 between driver and final on USB , 10 mV 1000 Hz with full power.

[lbcomms]

When i turn the pot VR9 to 50 % , the Concorde draws 1,9 A with the power on max

What output power are you seeing when it's as above (1.9A with the SSB audio gain half way)?

To see distortion on SSB, you need to have a two tone audio source and a much lower timebase setting on the oscilloscope.
If you haven't got one, an MP3 player or phone with a suitable sound file works quite well. You'll need to make a voltage divider (attenuator) with a couple of resistors and connect one end to a 3.5mm plug and the other to your radios mic plug. Resistors are nothing special, a 20:1 divider is close enough for most radios and can be made from 10K and 470 ohm components.

I can email the sound file or pop it onto a web page for you if you need it.

Once you have that up and running it's easy to probe around and see where things are falling over (flat topping). Practice on a known good radio first though, so you know what's normal and what is not.

[ballo]

I read 12 watts with ssb audio gain half way .

When i use 20 k ( 2 times in series 10 k) and 1 Kohm as a divider :

20k 1k
ground 0--I===I----0----I===I-----0 input (from mp3player or phone)
input Concorde

I made a very simple schematic diagram,hope i have it right what you mean ?

Thanks for patience by the way...

[lbcomms]

Here's the cable we use here:




Use the phones volume control or the radios mic gain to control the level.

You'll need a two tone sound file for SSB. The tones need to be equal in level and non-harmonically related to work. I use 700Hz and 1900Hz. If you want a sound file PM me and I'll upload it somewhere for you.

[ballo]

Thx ! I constructed the divider

I will PM you for the soundfile , thanks in advance !

[ballo]

Thanks for the files and i did the test with as result the photo of the scope.
This is full output on USB and measured at the antenna-jack.

When i decrease the audio , the audio gets bad audio.
Seems that the final stage is ok or...

[lbcomms]

You've got the timebase way too fast. It's showing the RF envelope which is meaningless as a test of distortion and linearity.

You need to slow it down quite a bit so it shows something like the waveform in the email, with 2 or 3 audio envelopes on the screen.

If you can't get it to lock onto the SSB waveform, put the radio on AM, and with a single tone, adjust the scope so it displays the classic AM modulation shape.

Then switch back to SSB with two tone. The scope settings will be very close to where they need to be to show the SSB waveform...

[ballo]

I tried to make see 2 or 3 waveforms bu i could not succeed. Strange .. i have a 60 Mc scope.

I did replace the driver and is the distortion is for a part gone.
Before replacing,i got good audio with bias on max but now i can go anywhere with this setting and the audio stays ok.
I tried your suggestion on AM but i can't get any TX audio out of the Concorde III ;-(

[lbcomms]

You need to set the timebase (SEC/DIV) to scan the screen at an audio rate to see the results of a two tone test.

1) Put the radio on AM and transmit without audio (i.e. a dead carrier).
Set the oscilloscope to 0.2mS/Div locked in the calibrated position. Set the Volts / Div to make the line go to a thickness of about 2.5 to 4 cm (1 to 1.5 inches).

Release the PTT. The line should go a lot thinner. Adjust the brightness and focus to get this line as thin as possible.

If you can't get that display, check your wiring and the other oscilloscope controls (such as input select).

2) Don't touch the oscilloscope controls once you have step 1 correct.
Transmit on AM again, but this time with single tone audio fed into the radio. You should see the classic AM modulation waveform:



If it's not rounded and smooth but is triangular or square shaped instead, the limiters have probably been removed from the radio. This is normally only a problem if the radio was imported from the USA.

3) Change the radio to SSB and the audio from single tone to two tone, key the transmitter, and measure again.

You should see a waveform very similar to the one above. You might need to adjust the timebase one step either side depending on the frequency of your audio tones.

I you get just a thick line like in step 1, then it's most likely a cut out or disabled limiter. Again, it's only likely to be that if the radio was imported used from the states.

Here's a just-acceptable SSB waveform below. In this case, the audio gain is too high or the ALC has been set too low:



The envelopes are just starting to merge into each other and are starting to flatten at the top. This is a sign the audio drive (or possibly the biasing) are on the high side. In many cases, a waveform like that will just pass, but might sound a bit rough on air.

In steps 2 and 3, you might have to go in-between timebase steps (i.e. go uncalibrated) and/or adjust your trigger settings to get a stable waveform display. The most common error is showing "ghost" envelopes, if this happens then your scope can't decide which one to trigger from and you need to tweak your timebase / trigger to help it trigger on just one of them.

Hope this helps...

[ballo]

Thanks ! This is a lot better to show

This picure is with 1 mS and 1 V on AM without audio but with the hum.
On AM i got no audio , only a hum and the rogerbeep is very distorded , on FM no hum and TX audio is very good.
On SSB without audio there's also a signal with a hum but TX audio is good.
Smeter is with transmit half way with no audio.
To decrease SSB mic gain and ALC does not help.

Think that the finalstage is still not that good.

[lbcomms]

There is no bias somewhere for it to be that distorted. Disconnect the base of the driver (2166) and look at on the trace that went to the base.

If it is still distorted there, work your way back to the mixer until you find the culprit.

If it's OK there, the problem will be in the biasing circuit of the driver and/or final. Check there is about 0.7V DC on the bases when keying on SSB with no audio.

[Otter]

Well, I am the lucky owner of said radio now. Once it arrives it's going to black spirit for him to work his magic on it I can do this stuff, but I work full time and Nick is better at it than me anyway.

[lbcomms]

He shouldn't have too much trouble finding the cause of an obvious symptom like that. Post the fault cause here when you / he finds it if you can for all to see.

[Otter]

Well apparently there was progress on it after the last post, but it still has issues. Apparently this is the current fault:

"The distortion is away but i have some hum on SSB and no audio at all on AM."