Hi guys,

... I've read a lot on the list lately about Hans' 50W PA ... but as it is only single band, I ask myself whether anyone of you guys has tried out the chinese multiband PAs for QRP radios, such as the MX-P50M or the MiNiPA50?

If I'd buy myself one of those, I'd want to use it with the QDX on 80-60-40-30-20 and alternatively with my FT-817 160-10 all bands.

They cost around $160 ... but the question is, will it be worth it? Are they solid, is the signal clean and are they suited for longer term operation? At least for the MX-P50M I found some positive reviews. --
But I also remember some OM complaining about dirty signals from these rigs.

I'm just for some portable extra juice, I can easily carry around ... Any ideas welcome ;-).

Vy 73

Stefan.

--
Stefan U. Hegner <db4st@...>
* * *
DB4ST --- German Ham Radio Station
D-32584 L?hne ----- Locator JO42IE
* * *
GPG-Key | C3CC 23A4 FBA8 622B 48AE
F-Print | 4F19 D0EE E39E ABDC 2BCE

My very first QDX QSO ( FT8 ) is in the log !
73,
Bill, N4QA
ps
This is a FINE little rig !

Bojan,
I connected W1-W0, W2-W3 and jumper at R3. No power.

On page 11, in the Assembly manual,? I see
C5
C8
C4
R6 pot
Are all these required and also PA + AND 5 volts jumper?

Charles Brown

Evan, you are getting this to a very concise set of steps. It is really helpful. What is the transmit current draw expected at the power supply on the QDX?
--
Colin Kaminski - K6JTH
https://www.qsl.net/k6jth/

Evan,

With your observations and suggestions I am quite sure now that my Q5 turned his head away when I was trying to PTT trigger the PA for the first time from an unmodified QDX.? But I have not noticed that.? Although I used a reduced output power.? My bad.? As for your suggestion about adding a P-channel MOSFET, I have an intention to add it at the PTT line input of the PA.? Since the QDX has a possibility to use a zero Ohm PTT line /PTT instead of a PTT +5V.

73 Bojan S53DZ

On Fri, Aug 12, 2022 at 06:19 PM, Hans Summers wrote:

?

used to send a notification email whenever any moderator approval was needed. Seems to have stopped! What changed? Now no moderation happens unless I got into the group on the web and do the approvals there. I have now set myself a reminder to do this every morning.?

On 28 Jul 2022, at 18:19, Jim Strohm <jim.strohm@...> wrote:

<snip>

Hey, do you think we'll get a surface-mount 4CX1500?

73
Jim N6OTQ

If there was a conduction cooled version that would be mounted on a surface :)

Stewart/G3YSX

Will,

The maximum current that the 50watt amp input should need would be 7ma.? The current would also go down as the voltage goes down due to a lack of drive capability.? This supports your measurements.?

The QDX drive puts the QSK transmit/receive MOSFETs in a marginal region.? Turning off enough to allow the output to bypass the two diodes and start feedback would then wipe out the finals.? A high voltage from a bad SWR would put a strain on the part of the circuit and could have been the reason that Q5 failed.? I would also check Q3.? Both are required for proper switching between transmit and receive.

If you do not use the QDX PTT to drive an amp higher than the 7ma under the full 5volt requirement, installing the 100ohm resistor in parallel should not hurt.? A better solution is to install a P Channel MOSFET to act as a buffer between the 5volt PTT high and the 7ma drive needed by the 50watt PA PTT input.? I would use ones like the AO3407 used for the reverse voltage protection circuit of the QDX or a BSS84 as used in the QDX PPT output.? This allows the QDX to be used in other amplifier circuits without the issue of a short on the PTT line causing a failure in the QDX.

I suspect that the issue would not come up under normal conditions.? I have used my rev 3 QDX to trigger a 40meter 50watt amp running on 13.8 volts without issue.? The high voltages produced in a miss matched circuit could be the main issue causing the failure.? Q5 failure indicates that RF fed back into the T/R circuit.??

Above are observations and suggestions.? They are offered free without any guarantees on my part.? You should check for errors.? Please let me know if there are any.

73
Evan
AC9TU

Hi Marc,

As Dan stated, the first step is to connect to a dummy load and verify that the current in receive mode is less than 140ma.? If not, you will need to remove the 4 BS170 MOSFETS and try again.?

Once the receiver works, you can test the low-pass filter selection by measuring the voltage on each of the 6 switching diodes D1,2,3,4,5, and 6.? The banded side of the diode (cathode) should read zero volts for the two diodes that select the band chosen.? The other four should be close to or above 5volts.? This should be done whit a dummy load connected.? You change bands using the RF Sweep function in the terminal program.

You can now go on to test the transmitter into a dummy load.? Do not install the 4 MOSFETs yet.? First, verify that there is 2.5volts DC on each of the 4 BS170 gate pins while transmitting using the terminal transmitter test program.? If you do not have 2.5volts on all 4 drain pads, you will need to replace IC5.

After you have verified IC5, measure the resistance between the source and drain on each of the BS170 MOSFETs.? It should be high.? I would guess over 1kohms, but I have not measured it.? If that checks out, reinstall the 4 BS170s and test the power output into the dummy load for each band.? It is also a good idea to measure current while transmitting (it might be hard to do when using your only DDM to measure power out).

Let us know if you find and fix the problem or the results of your tests if the problem is not solved.

The above are my recommendations.? I do not warrant that it is the best way to test.? It is what I have done in the past.
73
Evan
AC9TU

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How would I test this on my two amps. ??

QDX transmitter at N4QA gets its very first reception report via PSKReporter !

Hi all,
Just to report: Q5 was a bad guy pushing the PTT line to 2V.? I don't know the reason for the Q5.? I left the 100R parallel to R10 in the QDX in as I think this way the switching is more reliable.? Now the PA PTT input voltage?is +4.3V and current 5mA.
Funny enough the QDX / PA works the same but I am glad that the fault is repaired.
Thanks Ron. Thanks Adam.

73 Bojan S53DZ

I just received an Orange Pi 3 LTS and installed WSJT-X on a Debian image. CAT works fine but the soundcard setup is missing the "alsa_input.usb-QRP_Labs_QDX..." entries for both input and output.
There is an entry called sysdefault:CARD=Tranceiver in both input and output and they do work, sort of.

On the output side when I hit the Tune button I get the usual 5 watts.

But on the Input side I am unable to adjust the volume levels. It is very low but I am seeing a few decodes (the strongest stations). Is there a piece of software that needs to be installed?

Thanks,
Paul VA3ZC

Marc, have you tried putting it on a dummy load and measuring the output from the dummy load using a DVM? The best way to do this is using the terminal applications to transmit, so you can eliminate the computer as the problem.
--
73, Dan - W2DLC

Looking for some troubleshooting steps.? I can measure V,A,R,C,L.? No scope.?
9V build, after build and testing, I had power output on all 4 bands.? I put it in the case and lost 20M transmit, may not be the cause.
I have made contacts on 40M, now 40M has no power output.? I think the cause is tuning my mag loop was too much high SWR.? my loop doesn't do 80M, so that is why it survived?? I do have a solution to the tuning issue in the future.

What are the first steps to troubleshooting this?

--
Marc
N8LO

The PC, Willie !

QSL. Evan.
I just now adjusted ps vdc to 10.0 and now power out is 4.5 watts? ?perfectly legal for QRP !
Tnx, 73,
Bill, N4QA

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So, what changed?

Hi Bill,

Good news on figuring out the issue.? I recommend dropping the voltage supplied to the QDX to keep the output under the recommended 6watts maximum.? If your power supply is not adjustable, a couple of 1 amp diodes in series will do the trick.

73
Evan
AC9TU

Hot dawg !
Have a good match on 80m and getting 7 entire watts from QDX ! VDC drops from 12v to 11.8 on xmit and she's pulling about 900 ma xmit.
AS Rod Stewart always says " Tonight's the night !"
Tnx agn, guys & 73,
Bill, N4QA