Peaberry On the Air, mostly.

General discussion and support for the Peaberry SDR V2.

Peaberry On the Air, mostly.

Postby camqrp » Thu Jan 01, 2015 12:20 am

Chased most of the bugs and have made contacts on SSB, JT65 and Hell using the Peaberry. At about 750 mW out on 15 meters I've managed JT65 Qs to Hawaii, Japan and the East Coast from here in CA. It works!

I'm powering the rig with a small bench supply which has both voltage and current metering. Good thing because after a few Qs I noticed that the current draw in receive mode, which is normally about 200 mA, was not dropping back to that level after I finished transmitting. It stays at about 400 mA. I have to cycle the power off and back on again to get it to drop back to 200 mA.. It was difficult trying to figure out where the extra 200 mils were being used until I grabbed hold of the PA heat sink. Now it seems the PA is still turned on during receive but there's no RF going out and the receiver is working.

To start trouble shooting I've measured the DC voltages at a couple critical spots, hopefully one of you can check and see if these are what they should be:

At the junction of R35 and R36, I have 0.0 volts in Receive mode and 10.6 volts in Transmit mode.

At the junction of C23 and R45, which is also the voltage at the secondaries of T4, it's 0.74 volts in Receive and 2.1 V in Transmit.

Also, the TX line coming from the PSoC measures at about 0.7 volts in transmit mode, I'm guessing that this should be at the 5 volt level. That would suggest that either Q4 or Q10 is bad, but the switching voltage above suggest that these transistors are working correctly.

Tnx, Cam
camqrp
 
Posts: 36
Joined: Tue Oct 07, 2014 12:02 am

Re: Peaberry On the Air, mostly.

Postby W4MMP » Fri Jan 02, 2015 11:31 pm

Also, the TX line coming from the PSoC measures at about 0.7 volts in transmit mode, I'm guessing that this should be at the 5 volt level. That would suggest that either Q4 or Q10 is bad, but the switching voltage above suggest that these transistors are working correctly.


Hi Cam,
The TX line attached to the base of Q4 definitely swings between 0V and 5V with 0V actually being 0 volts. It really appears there is a marginal solder connection somewhere in the bias section of the PA that changes with temperature. May I suggest simply touching up everything in that area with the iron.
73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Peaberry On the Air, mostly.

Postby camqrp » Sun Jan 04, 2015 8:22 pm

Ron -

I touched up the solder on all of the components in the bias circuitry but no change. So I then started lifting active components starting at Q5 and working backwards toward Q4. It wasn't until I lifted Q4 that I got the TX line to show 5 volts. Seems like Q4 itself is the culprit, so I pulled it and replaced it with a regular TO-92 sized 2N3904 (no spare MMBT3904s on hand). No go, even with the collector left disconnected. Seems like all I have to do is connect the base and the emitter of the 3904 and the TX line gets pulled down to 0.7 volts in Transmit mode.

It doesn't look like the TX line goes anywhere else in the circuit, at least I can't see any other TX connections. SO I'm out of ideas at the moment.

Cam
camqrp
 
Posts: 36
Joined: Tue Oct 07, 2014 12:02 am

Re: Peaberry On the Air, mostly.

Postby W4MMP » Sun Jan 04, 2015 8:45 pm

camqrp wrote:Ron -

I touched up the solder on all of the components in the bias circuitry but no change. So I then started lifting active components starting at Q5 and working backwards toward Q4. It wasn't until I lifted Q4 that I got the TX line to show 5 volts. Seems like Q4 itself is the culprit, so I pulled it and replaced it with a regular TO-92 sized 2N3904 (no spare MMBT3904s on hand). No go, even with the collector left disconnected. Seems like all I have to do is connect the base and the emitter of the 3904 and the TX line gets pulled down to 0.7 volts in Transmit mode.

It doesn't look like the TX line goes anywhere else in the circuit, at least I can't see any other TX connections. SO I'm out of ideas at the moment.

Cam


Hi Cam,
I will pop the case top off one of my Peaberrys and make a quick measurement and get back to you with the voltage level at the base if Q4.
73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Peaberry On the Air, mostly.

Postby W4MMP » Sun Jan 04, 2015 9:23 pm

Cam,
I stand corrected. The voltage at the base of Q4 goes to .68v in transmit mode (this makes sense when measuring the voltage at this point. We are measuring the voltage drop across the base to emitter junction. The collector of Q4 drops to almost zero (.02v). This applies zero volts (.02v) to the gate of Q10 which causes the drain of Q10 to go to 12.8v (on transmit). This is when using a 13.8v supply.

Sorry about the miss information.

When trouble shooting the PA, keep in mind several things:
1) The PA MOSFETs (BS170) are kept in an off state by applying near 0v to the gates. When in transmit mode the bias applied is approx. 2.5v.
2) The driver (Q9) is off in receive mode with 0v at the collector. On transmit approx. 12v is applied to the collector.
These are the key voltage levels you are looking for.
73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Peaberry On the Air, mostly.

Postby W4MMP » Sun Jan 04, 2015 9:31 pm

Cam,

The first place to check is the gates of Q7 and Q8. These must be a near zero when in receive mode.
73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Peaberry On the Air, mostly.

Postby camqrp » Mon Jan 05, 2015 5:02 pm

Ron --

In Receive mode the gates of Q7 and Q8 are at 0.75 volts, increasing to 2.0v in Transmit.

Measuring backwards, base of Q5 is 2.6v on Transmit and 0.02v on Receive.

The Gate of Q6 is 2.6v on Transmit and 0.0v on Receive.

CAm
camqrp
 
Posts: 36
Joined: Tue Oct 07, 2014 12:02 am

Re: Peaberry On the Air, mostly.

Postby W4MMP » Mon Jan 05, 2015 5:35 pm

In Receive mode the gates of Q7 and Q8 are at 0.75 volts, increasing to 2.0v in Transmit


Cam,
That is too high (and too low). In receive I measure .2v and 2.65 in transmit mode. I'm not sure where to go from where. There is obviously something wrong in the bias section but my guess is one of the resistors in that section has a marginal connection. Hopefully someone else will chime in
73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Peaberry On the Air, mostly.

Postby camqrp » Mon Jan 05, 2015 7:17 pm

OK, that "off" voyage seems too high. I'll do some poking around.

Tnx
camqrp
 
Posts: 36
Joined: Tue Oct 07, 2014 12:02 am

Re: Peaberry On the Air, mostly.

Postby AE9RB » Mon Jan 05, 2015 10:42 pm

camqrp wrote:In Receive mode the gates of Q7 and Q8 are at 0.75 volts


Yep, that's not right. Maybe R33 isn't soldered? Q10 should shut off completely when not transmitting.
73 David AE9RB
AE9RB
Site Admin
 
Posts: 511
Joined: Thu Nov 15, 2012 5:27 am
Location: Portland, Oregon, USA (CN85ql)

Next

Return to Peaberry SDR V2

Who is online

Users browsing this forum: No registered users and 2 guests

cron