Interesting experiment. I had a miserable half a watt out of my 20m unit after completion at 13.8V DC which was a bit disappointing. In fact I was a bit deflated and put it away for the night. The next morning after some coffee, I stuffed the input signal of the filter on the scope and it looked about right for the expected 3.5-4W out so suspected the filter design. I yanked all the parts off and substituted the values in from the GQRP documentation on LPF design here:??... I naively assumed 50 ohms output from the PA which isn't necessarily the case but it worked. Got 4W out at 13.8V DC which is good and no heating problems with the PA throwing out WSPR into a dummy load as a test case.
I have since converted it to 30m which is a little quieter and easier to navigate as it is contest free. Unfortunately I appear to have knackered something during conversion as the audio gives out on the receiver and haven't had the time to fix it yet. Oops. Moral of the story: band conversion is risky; just buy another QCX :)
Chris
M0XTE
On Mon, 6 Aug 2018, at 15:51, chokelive E29AHU wrote:
Hi All,
I would like to share my experiment.
After a several month i have fixed output power for my QCX 20M? (my kit No.#487)
and now i can getting with full power 5 Watts @12Vdc
before I solve my QCX 20M. I can get output only 1.5 ~ 2w maximum
First i observe LPF circuit C25 and C26 (390pf) getting very hot during transmission.
This is my modification.
1. remove 1 turn of L1 and L3 (use only 15 turns) --> power improve abit to ~ 2.5w
2. remove C25 and C26 (390pf) and i replace with 2 series of MLCC capacitor 680pf (because there are in my stock) --> this big improve my power to 5w !!!
I believe?my issue is mismatch at LPF especially?at C25 and C26 (390pf).
thanks group for good knowledge?sharing?and Hans for the grate kits.?
73
Choke E29AHU
during experiment
finally soldering in the right place
output power @12vdc
