I've made some progress on Q11 overheating, and 'crud' in the modulation on this unit.  Various bypass capacitors on Q11 seemed to help, but I didn't think that the FET was cool enough and the envelope didn't seem as clean as it should be.  So I decided to take a look at why the device was running with so much current.  To make a long story short, I paralleled R43 with a 470 ohm resistor. This lowered the drive to Q12 and thus reduced the excessive current through Q11.  Now the transistor runs cool.  There appears to still be sufficient modulation capability in both directions, and the spurious signals now appear to be gone.
--
Jeff W9GY Calumet, Mi (UP)

Reminder: Wednesday Evening 40 and 80 meter Nets

When: Wednesday, 6 November 2019, 8:00pm to 9:00pm, (GMT-06:00) America/Chicago

Where:40 and 80 Meters

View Event

Organizer: jomatlock@...

Description: The 40 Meter Net will be at 8:00 pm DST central time  on 7.122 +-. QRM
NCS is WQ5RP Terry.

Wednesday evening 80 Meter CW Net. will be at  (8:30PM Central DST Time Wednesday). 
The 80 meter net will be called on 3.564 MHz +/- QRM.
Net control operators are Johnny AC0BQ or Paul N0NBD.

* NEW *  Wednesday evening DMR Voice Net will be at (Thursday) 0300 UTC (9:00PM Central Time Wednesday/)
Four States QRP has a Brandmeister DMR Talk Group (TG31654). Join us to discuss QRP, ask questions, or just ragchew. The Wednesday net is a directed net  but any other time you may use the Talk Group to chat with other QRPers.
Net Control operator is Bert NØYJ.

I bypassed the gate of Q11 with a 1 MFD electrolytic as suggested by Bob, W9RAN.  I now get  modulation envelope above and below the unmodulated carrier, which is what I would expect.  However, the device is still running too hot.  More later...
--
Jeff W9GY Calumet, Mi (UP)

Bob, that seems like a good insight.  I have a suspicion that there may be an underlying cause, possibly a manufacturing issue causing the small SMT transistors to leak.  My operating theory is that there may be some solder paste under the SMT parts that is allowing some current leakage.  This would cause Q12 and Q11 to be turned on simultaneously, resulting in the high dissipation you observed, and may cause the oscillations you are seeing.  I'm going to do some checking to see what I can find.

That seems to be about what mine puts out, but it made a perfectly fine AM contact with it the other day with it. Remember, that’s less than 3 dB down from the advertised level and it doesn’t make that much difference in your transmitted signal. The receiver doesn’t seem to be wildly sensitive, but I think if it were I think it would overload. I set my modulation by the LED activity, with it flashing only on peaks. WTWW (5085) sounds great, as does the net that meets on 3885. I don’t think I will mess with mine. The enemy of good is better!

73,

Charles - NK8O

--

Hello,

I just received and built a QRPometer. It is a 1st class kit. It is not my first kit, but I have not built many. The board is one of the best I have seen and everything fits as it should.  The SWR readings are perfect the power readings on several QRP rigs give a good comparison between the rigs, but I am not sure if they are correct, and if I assembled something incorrectly. Here are my readings:
Cricket 40 @9v - reading 0.13, @11.5v - reading 0.20
Pixie 2 @9v - reading 0.09, @11.5v - reading 0.15
ATS-3B @9v - reading 0.23, @10v - reading 0.35, @11.5v - reading 0.40
I also tested an Elecraft K2 and IC-7300 with power from 0 to about 12 - the readings went up then down, but did not seem close to what the radio meters were showing

I did re-solder the pads on the Velleman meter, but perhaps this is not correct.

Thanks

George VY1GP

Dave:

I know I can't see all that well.?? I also know I don't know everything.?? I also know that I haven't been getting the memos especially since I have been older.?? However, I have worked hard, studied extensively and have a basic understanding of how this stuff works.?? I guess this type of thing comes from the plug and play mentality and a lack of undestanding of how all the basic stuff works.

I just couldn't shut up afte reading your latest email.

Lee, W9HIF

Brian-

The Nouveau-75 conveys information (your voice) by Amplitude Modulating its carrier signal.?? PSK, by contrast, is expecting a steady signal- a tone with phase reversals to signal 1s and 0s. A setup listening for PSK signals from an AM rig won't decode anything intelligible.

There's also the matter of the bandwidth it uses.?? Your transmitted AM signal has both upper and lower sidebands present at equal power levels.?? It may well cause QRM to other operators up to 5-6 kHz away, and that's less-than- ideal practice in the digital portion of the band.

73- (The Other) Dave- K1SWL

On Sat, Nov 2, 2019 at 2:59 PM Brian Crittendon via Groups.Io <aaa5mi=yahoo.com@groups.io> wrote:

Is there any reason we couldn't use this radio with PSK?

-- 
Lee, W9HIF
The station of the Scary Ghost Stories and Tales of the Glories of Ham Radio long, long ago.

Now that I've got my modulator settled down I'm wondering what others are seeing for RF power output?

With a 13.5VDC supply I get 2.8 watts resting carrier and right at 11 watts PEP on voice peaks with 100% modulation.   That was good enough to be heard around the midwest this morning on the Midwest Classic Radio Net, but it's about half of what the Nouveau 75 specification says it should be.

Some comparisons will help determine whether my modulator is still not working right, thanks.

73, Bob W9RAN

You might consider joining the "CalQRP" group on Groups.io. Ken WA4MNT announced the product on that list, and I think some of the QRP Guys are all on that list. You might post to that list with the issue you're having, and see if anyone there can make suggestions.

--
Jeff N0̷MII

Dave,

I've got a band-aid that seems to prevent the thermal runaway from happening but I'm hoping you can provide some insight into "why" and perhaps a better solution.

I found some nasty looking oscillations when scoping the gate of Q11 to see why it was turning on - several volts of unstable crud in the 600-800 kHz range.  A 1nF cap to ground reduced the amplitude and shifted the frequency to the 225 kHz range, so I tried higher values.   As much as 10uF reduces the oscillation without noticeable impact as now for the first time I have positive peaks and 100% modulation (even though I see some spiky things on the carrier which I suspect is the same oscillation).

The problem apparently is an instability in the modulator circuit that I'm just minimizing so the circuit can work but and hopefully this will enable you to get a handle on what's really going on. Meanwhile I think I'll try the radio on the air tomorrow morning!

73, Bob W9RAN

On 11/1/2019 1:30 PM, nm0s_qrp via Groups.Io wrote:

voltages measured for Q3 and Q11 swapped

Ah, no, but I read "IRF-510" and forgot there were two of them, and I was measuring Q1 instead of Q12.   Thus my argument about 0 volts on the drain and resting carrier, etc.

Let me try again with new measured values:

           G        D       S

Q3    9       10.3      12.6    FQP7P06

Q11  7.5    3.5*     12.4    FQP7P06

Q12  5.6    3.5*     2.4       IRF510 (NOT the PA one!)

*  the voltage at the drains of Q11 and Q12 measures 3.5V right after the PTT is keyed, but start to rise rapidly, which creates the thermal runaway problem.   The voltage is > 8 volts within 15 seconds or so and when I measured the temp of the Q11 heatsink it quickly rose to > 50 deg.

As with the values your provided, all the above are with PTT keyed but no modulation.

Sorry for the mixup on Q numbers.   Does this suggest anything new?

73, Bob W9RAN

In the receive mode, all three of these MOSFETS should have no drive, i.e. the gate voltages should be close to the source voltage.  Bob, I think you have the voltages measured for Q3 and Q11 swapped, as the drain voltage you report for Q3 is the same as the drain for Q12.
It looks like the gate voltages on Q11 and Q12 are not correct.  I would suspect failure of Q10 or Q13.  These would be the ones I would try replacing.

73 Dave

On 11/1/2019 5:39 AM, W9GY wrote:

Hi Bob, got same issue on mine.  Q11 get real hot real fast in tx.  I'm awaiting some FETs to arrive before additional troubleshooting.  Please keep me in the loop as to what you find. -

Hi Jeff,

You bet.   The only one I've heard was WA8SAJ's and it sounded good thru a linear.

When I first noticed that Q11 was burning up, I saw that the tab of Q12 might have contacted Q11's heatsink.   But while I was waiting for replacement FETs to come I realized the drain of Q11 and Q12 are connected together in the circuit anyway so it wouldn't have mattered if they were touching.

So we both received defective PC boards it seems.   The more I try to understand what's going on with this modulator the more confused I get!    A complete set of voltage measurements from key nodes - each terminal of all active devices at a minimum - would be a big help.

73, Bob W9RAN

Hi Bob, got same issue on mine.  Q11 get real hot real fast in tx.  I'm awaiting some FETs to arrive before additional troubleshooting.  Please keep me in the loop as to what you find.  -73-
Jeff W9GY Calumet, Mi (UP)