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Any tryed to mod the qcxmini for lower power and better battery life.
I like to run QRPp wirh a PP3 9v battery on a Rockmite with power 100mW, but would like to have a mod to run qcx transiever on 100mW low and 1W high.? Would like to have any tip .Posible it can use the AGC controll signal to do this or a spesial program version.

On 25/02/2024 15:34, LA1KHA Kjell wrote:

would like to have a mod to run qcx transiever on 100mW low and 1W high

Kjell,

I would try using a lower voltage, maybe a QCX would work as low as 7.5 volts.
Separating the PA power feed would enable lower voltage, lower power out.

73 Alan G4ZFQ

I run my qcx+ at 8v with 1 watt out for wspr. somewhere between 8 and 7 v the rig display starts to fade on tx. My mini will run down to 7v but is still doing 1 watt at that point.
I too would like to run it lower if anyone figures out how it can be done.
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regards,
Bryan, N0LUF

SOTAbeams, a company in the UK, sells a "Milliwatter extreme" that is a 5 watt, 50 Ohm attenuator, with a choice of 10 dB or 17 dB attenuation. The device attenuates the transmission, but bypasses for reception. I have used mine for WSPR tests and it worked well for me.
This solution is not going to help with extending battery life, though.
Ian VE6IXD

The power reduces as the input voltage does -?
IIRC the ‘raw’ supply runs the last few op amps on RX, the backlight and the PA.

The limit is around 7V into the 5V regulator which is more like 7.5 at the input jack, ?the backlight and OP amps are still just about OK at that level ?

Kjell,
When I'm in a mood for QRPp, I haul out my Zachtek "Flea" transmitter and the ATS-25 general coverage receiver I use with it. It's only 300mw, on 20, 30, and 40m. It doesn't have to be that particular receiver, I just chose that one because Harry from Zachtek used it for his own Flea and knows it works properly. The Flea handles antenna swapping between the receiver and transmitter, and it has a very imaginative frequency spotting feature that makes it dirt simple to find the transmitter frequency. It's a VERY small transmitter, about the size of an index card. The receiver is actually larger than the transmitter in my case. I power the transmitter using a USB-C Power Delivery battery bank and a 12v trigger cable with the correct DC coaxial barrel plug on it. I have a link dipole for 20/30/40m that's resonant in the CW portion of each band, so I don't even need to tune the antenna, just make sure the correct links are connected.

I used this setup at Field Day a couple of years ago, and was making contacts 800+ miles away from our ham radio club's usual Philadelphia-area camp in a local State Park that has camping. I was being heard quite effectively near the Illinois-Wisconsin border and thereabouts.

For those concerned, the PD setup I use is not plagued with birdies or other noise. I routinely operate out and about using such power supplies. I do have a couple of LiFePO4 12v batteries that I can bring to bear, but they're heavy and bulky, and need special chargers. (Not as heavy as the Sealed Lead-Acid Batteries I was using prior to LiFePO4 availability, but still heavier than a 10-20Ah USB-C PD power bank. I've even operated using the 4,000mAh PD bank I keep in a pouch in my pocket. Works great. I had an article in QRP Quarterly some years ago that showed my first PD trigger board (I found it on Tindie) connecting a compatible PD power bank to one of my original QCX radios. As long as I used the correct size of barrel plug, it always worked like a champ.

But I do seriously recommend the Flea as a very useful QRPp transmitter. It's also relatively inexpensive.?



The software for the Flea was created by Kevin Loughin, KB9RLW. He has a whole series of YouTube videos on the Flea project, from various stages in development. He also operated at Field Day, using a Malahit receiver. Kevin hasn't been doing a lot since he caught Covid and was laid low with Long Covid and is still having difficulty getting back into the swing of things. Here's his video relating his Field Day operations.



Worth a look, even if you never get your own Flea.

73,
Gwen, NG3P

Links to SotaBeams switched attenuator (switched in by relay on transmit/switched out when not transmitting, on receive)






?
The schematic should? be straight forward to homebrew ugly/Manhattan style, with individual choice of attenuation level(s), and? powered by a battery.

In fact this is just what I plan to build very soon for QRPp WSPR but should be fine for CW

73
Chris
m0pzc

On 26/02/2024 22:52, Chris m0pzc wrote:

Links to SotaBeams switched attenuator (switched in by relay on transmit/switched out when not transmitting, on receive)

Chris,

With respect this sort of thing is good for black box users.

But my feeling is that generating "vast" amounts of power then wasting it in an attenuator is not really true QRP.
I think reducing power output on all QRP Labs TXs can be achieved by reducing PA voltage.
I guess there will be a limit, even with 0 volts on the PA something will get through.

73 Alan G4ZFQ

The easiest mod is to remove 2xBS170 and run on one BS170. QCX will be in QRPp range now with this mod.
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73, Barb

On 27/02/2024 11:19, wb2cba@... wrote:

The easiest mod is to remove 2xBS170 and run on one BS170. QCX will be in QRPp range now with this mod.

Barb,

I wonder.
I seem to remember that essentially the paralleled devices share the load. That has been mentioned with the U3S.
Would just one be overloaded?
In any case if the power was reduced to 1/3 it still would not be QRPp depending on the definition of QRPp:-)

73 Alan G4ZFQ

Hans,

?I have QCX V1 and I adapted for usdx and used it with 1x BS170 without any problems many months. The PA efficiency is 60 to 70% which does not create significant excess heat.

?Actually that QCX is my QRPp rig which I still enjoy. I know that usdx is not the QCX firmware though I think they share the same QCX ghetto class E PA design regardless of firmware as hardware topology.

I like to experiment and this suggestion was through my experiments that I carried out so ?here is the disclaimer listen to Hans and do not try this at home if you are not into experimental ham radio operation!:)
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73, Barb

You are right Hans! I forgot to mention the most important point! I lower voltage to 5V! Getting old!! Sorry for the snafu!
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73, Barb

?? I agree!
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73, Barb

Just to make sure I understand the theory...? 3x BS-170's @ 5v would still result in the same QRPp power out as Barb's 1x BS-170 @ 5v?

Thanks
Jon n0wl

Correct! In my case I smoked out two of the BS170 and ended up with one heathy BS170. QDX is ?still alive and kicking with that one!:)

3x BS170 is absolutely a better option to distribute output power.

So to summarize here is my QDX QRPp setup:

- removed IC2 - 78M05 from pcb.?

- USB socket 5V pin goes to IC2 - 78M05 5V output pin

- In my case one BS170 is active but 3xBS170 is better.

- No 12V connection.

- The whole rig is powered by PC USB. RF power output around 500 mw to 700 mw band dependent.

The advantage of this setup is I carry only my laptop, ebd fed half wave antenna and ?QDX to Park. No PSU. PC supplies at least two hours of continus fun. My laptop is a microsoft surface laptop.
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73, Barb