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Stefan :

I own one of the Chinese-made MX-P50M amps and I like it.?

I have not yet used it with a QDX as the only QDX I have built at the moment is a REV1 with no external PTT connection.
I have however used the amp with my IC-705. With about 2.5w out on the IC-705 I can get 25 to 30 watts out of the amp.? I bought the amp because the reviews I saw were all positive and a UK Ham looked at the spectral purity of the amp and it is very clean so long as you don't drive it too hard (i.e. probably best to keep the drive somewhat under 5 watts).??

If you are considering buying one then I suggest that you plan to make the simple keying mod suggested by Kevin, KB9RLW? described in this video :


He also has links in the description of this video to the blog with the spectral purity tests.?

The following video has someone doing KB9RLWs mod and it includes a schematic near the beginning so you can see how simple the mod is :


It is very much a no-frills amplifier (manual band switching and manual keying via external PPT to ground, using relays)? but it is well constructed, with clean output and the price is very reasonable. I suggest buying on Aliexpress. They also show up on the Amazon marketplace but the prices are always much higher.?

I am waiting on building my REV3 QDX until I hear the definitive news on converting it to operate on the some of the higher bands. I plan to occasionally run this QDX with? a slightly reduced supply voltage to get around 2.5 watts out to drive the amp.

Cheers

Michael VE3WMB?

I still have to run the configuration and change the fall threshold from 255 to 60 every time I power up the QDX, a real nuisance. I tried entering 60, saving EEPROM.qdx to disc and then writing it back again. I also updated to 1.04 and did a factory reset. Still the fall threshold comes up as 255.

255 is all ones in binary so I am thinking my board came with one defective memory byte in the EEPROM. Or could it be something else?

Any suggestions as to what I should do next would be appreciated.Thanks.

Jim AJ8S

My hesitation would be inadequate lowpass filtering.
Do the Amps have proof they comply with the FCC requirements? If not I would not purchase one.?
This is important because your harmonics are spotted these days with the numerous stations monitoring.?

Any equipment that doesn't have FCC compliance
can also cause other noise. I think Tokyo High power were pretty good. I would look on ebay for one or similar.

Thanks for the clarification, measured the current at the output of the buck converter. ?.19 mA, which at 9V gives me 170mW on receive. ?I hope that means I’m not pulling transitors?
--
Marc
N8LO

Yep, noticed it. Put a few more score marks in the groove with an exacto blade and they popped right off.?
Thanks for your response though.

It’s just a PCB finishing error from the factory. There should be a groove cut into the PCB, you just snap it off using even pressure. If there is not a groove then you may have a bigger issue.?

Yes, you need at least:
C1, R6, R5, Q1, C4, T1, C5,
to come with the signal to the LPF.

Yes PA B+ connect to +5V.
you have W1-W0 and W2-W3 connected instead of a relay.
I would in your case try a resistor from PA B+?(+5V)? to MOSFET drain instead of T1.? I don't know what output RF level you need.

Your power supply goes to +5V and GND.
Your RF output is at RF or RFO.

73 Bojan S53DZ

Normal receive current at the power supply is 140-150mw.?
--
Colin Kaminski - K6JTH
https://www.qsl.net/k6jth/

I have been testing with a dummy load using a standard SWR/Power meter to determine if I am getting power to the dummy load. ?Is that what you mean? ?I can tell you software is not the issue. ?I have run tests using WJTX to trigger and the terminal app via putty.
--
Marc
N8LO

Question: ?The current in receive mode where? ?Where am I measuring current. ?The draw from the power supply? ?
--
Marc
N8LO

Building my second QCX and at the point of installing the jacks and the IC11 (instructions 3.48). It seems that the PCB was not trimmed properly and there is 5mm of material on either end that shouldnt be there. Has anyone else seen this or am I special somehow?

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