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Looking at the schematic, the TX line switches both the drive to the final and the reverse bias to the diode switches in the LPF.? If separate lines from the uC were used for these two functions,

Charles Johnson KF4AYT Because you apparently do not understand series and parallel circuits. R4 is in parallel with the winding of T1, that has a very low resistance and you never See R4 with a

Short answer, yes indeed. For QRP the toroid core can be quite small, one inch or even smaller. For example, the output transformer in the QDX is handling 5W, and it is magnetically equivalent to a

At the risk of extending the off-topic thread, but since you asked, an FT140-43 is fine for QRP but use 3T/21T instead of 2T/14T. Same turns ratio but better primary inductance for the smaller core.

Martin, I was wondering about your capacitors C67, 68. I remember someone suggesting it on the QCX, Hans said no, it must have 0-5V drive. For full power you may need to ensure it can have this, pull

I use a 41 m EFHW for my station and it works great. About 12 m above ground. I was lucky to get a roll of army twin field phone cable. 800 m makes a lot of material to build antennas from. Important

Dear Alan, Thanks! I should have been more clear about what I am actually working on: I am designing a QRP CW transceiver that should provide 5 W from a 2S Lipo (7.4-8.4V). In previous designs, I used

Hi all The Rev3 manual is now published see http://qrp-labs.com/qdx . There are still 187 QDX remaining in the shop http://shop.qrp-labs.com/qdx . We have started shipping QDX kits but getting through

Addendum: The MPS751 can handle 2A as per the datasheet ( https://www.onsemi.com/pdf/datasheet/mps751-d.pdf ), so the main question is how we can drive it to that current with the desired timing of

Hi, has anyone pursued this further so far? IMHO, one should be able to use the basic QCX key envelope circuit but with a stronger transistor, because the push-pull PA draws a higher current than the

Martin, Can't this just alter the PA voltage? Maybe a LM317 with switched adjustment resistors. A proven, simple way that needs no PA mods. I can not comment on your circuit but I do suspect it may

Should I want to realize a more compact version for QRP only (10-20-40m with total radiator length of 12 m, not so much interested in 80m), may I use a 140-43 toroid instead of 240-43? Would the same

Dear Hans, all: First of all, a big thanks for the QDX PA design! And for the great "design" sections in all of your manuals that are a great source for learning! I tried to add a DAC-controlled bias

Hi Ben Seeing is believing Try and see :) 73 muhsin TA1MHS

I built a Z match tuner from a circuit which is almost the same as the Emtech. It was a fun build and the component cost was very low. It also helped me better understand the theory behind it as well.

Pedro, What version of the QDX? What firmware? 73 Alan G4ZFQ

Hi Mike, yes i've seen the qrpguys products as well. However, I didn't know them at the time I ordered the Chinese kit. They're probably a lot better, but this one now works well enough to try out for

Nice mods! I've also modded one - yellow core, fewer turns, extra capacitors switched in, and a 3-watt resistor in the tune bridge. Carol Milazzo's blog is also very useful. I use mine with a random

You’re right about the Z match being wide-range. The price is at the high end, but I’m happy with my EMTECH ZM-2. After doing a lot of reading up on portable antennas, I opted for non-random over

Having owned a Deere, and having farming neighbors who also owned Deer tractors, I may have been lucky in that we had a dealer 3 miles away.? I had no problems at all getting parts.? And in