The weather this morning turned out to be good enough for a short activation of the Hochglaserer (OE/ST-482). I took both my QCX 80m and new QCX Mini for 40m:
Unfortunately, my 80m endfed did not like running past so many trees and I couldn’t get a satisfactory tune on 80. It was all down to the untested QCX Mini:
Conditions were pretty appalling today and several stations did not make it into the log due to QSB, sorry if you missed out. I’m not used to the keyer in the QCX Mini, so there was also a bit more QLF than normal. Generally though, I was very happy with the QCX and am looking forward to better conditions. The snow is melting at the moment, so many mountains should be accessible in the New Year:
I completed my Mini today and gave it a quick test in the garden. It’s the 30m version and range seems less than my 20m QCX+ which can usually contact a few RBN spotters on the east coast of Canada and the US but the coverage in Western Europe seems good. I will have a fiddle with the windings and see if I can tweak it a bit.
I’m still waiting with baited breath for my replacement BSS123 (Q5) to arrive from Mouser so I can replace the one that appears to have been defective on my board. Should be here Tuesday.
Now I have to go back and re-work L2 that I had dorked with trying to figure out my low power issues. Since Q5 is the last transistor before the LPF I’m sure that had something to do with it.
@N1RBD
Hi Richard, I hope you get your transistor soon, this toy is soooo much fun!
Yesterday I had my first DX contact, with W3NP, Dave in WV, who is also an SKCC member like me.
I contacted him twice, first on 17m, and then again on 20m, with only 3.5W and a groundplane antenna.
WOW, just WOW!
In the mean time I found out that the sensitivity on 20m is roughly 5dB less than that on 17m, so good enough for QSO’s, but you could also say that the BPF in the QCX is not very good
I added more details on my blog, about RBN reports and the QSO’s I made so far (see link in a previous post above). Still to add: some spectrum analyzer measurements.
@DM3FAM
Hi Marcel, you have been added to my “Hall of Fame” … I have added a paragraph in my blog post about making an extension cable like yours. Thanks for the excellent idea !
Luc ON7DQ
I had problems measuring and checking without the extension cable. Now I have enough space. Interesting blog from you. I have already found some good information. Thank you very much. See you in the next QSO.
Today I did some tuning of the toroids in my 17m QCX Mini.
I changed only L4 and L3, and could raise the power to 5.6W (at 12V DC input).
Power on 20m is now 4W.
Luc ON7DQ
Fantastic Luc,
looks like my next purchase will be a QCX Mini for 17m; two bands for the price of one. I use a Fuchs antenna (with my small CW only rigs) so I should get some additional harmonic suppression.
73 de OE6FEG
Matt
Luc, the measurements you are reporting are much more than Han’s claims. For example, with a 12v supply he says 3W is the expected output.
My measurements, based on the voltage at a 50 ohm dummy load, also show 3W with a 12v supply. Both my 20m QCX and 40m Mini give the same result.
I haven’t done anything to the LPF toroids yet because the power output seemed to correspond with what QRP Labs said I should expect. Perhaps I need to re-think.
It looks like you can read my mind.
I was just testing a lightweight Fuchs antenna for 20m and 17m, hi.
It’s hanging indoor now, from the attic along the staircase, to the ground floor, but seems to work OK. Only I took a high brightness LED, and it is on all the time with 5W, maybe I should take an old LED, or put a Tiny SWR in the tuner.
I will take it outdoors as soon as I can, and do some tests with it.
I made the wire 7.9m for 17m, and adding some 2.20 m should make it work for 20m. My tuner circuit resonates on both bands, and even on 21 MHz, but I don’t have a QCX for that (yet !) .
HNY es 73
Luc ON7DQ
Well, I finished my QCX-mini build but despite taking much care, the rig is not working
Thankfully the smoke test went okay, however I’m stuck at the alignment so far. I suspect that I’m suffering from the dead op-amp issue that seems to be fairly prevalent. I do have some NE5532 in SOIC-8 that I bought for a project on my long ‘to do’ list.
In terms of power output, I’m getting 4.6 watts output at 12v on 30m. I adjusted the toroid windings for max output but I didn’t remove any turns. I suspect that if I removed a turn from the toroid nearest the PA stage, I’d see a bit more power but I’m happy with what i have.
Hopefully I’ll track down my receiver issue soon, either with a DVM or firing up the ancient Tek’ 465.
I went through the procedure on my QCX 80, and whilst I did squeeze an extra watt out at 12V, the change was not as dramatic as with the higher band kits. My guess is that Hans got a bit sick of people complaining about low TX . Something else that is useful to know, is that if you move the CW filter centre frequency, as detailed in the modifications, it is very likely that you will see a lower peak (below 7) when you come to peak the BPF. However, there is nothing fundmentally wrong with the RX.
73 Matt
The power curves in the manual were measured back in August 2017 with the original classic QCX. The schematic and performance of the QCX+ and QCX-mini are substantially the same.
Now the expected power output is generally higher due to:
Since January 2020 we have been using only micrometals toroids supplied via http://kitsandparts.com - these generally provide slightly better performance than the previous toroids.
Since January 2020 we have been using only Vishay NP0 capacitors sourced via Digikey US - particularly on higher bands these capacitors have lower loss than the previous NP0 capacitors used.
I learned how to better adjust for best power output, and documented it on the YouTube video
After these three improvements (incl #3 tuneup if necessary), you should be within 1/2 a Watt of 5W at 12V supply, sometimes more than 5W; and by 13.8V you’re really cooking.
Note that the purpose of the 12mm washer is NOT to act as a heatsink. It is a very poor heatsink because it has very little contact area with the transistors (actually ZERO contact area since their curved surface touches the washer. The purpose of the washer is to apply force to the transistors to firmly secure their flat side against the PCB groundplane. The PCB groundplane is the intended heatsink.
After a bit of investigation with a DVM, I suspected that op-amp IC9 was faulty on my QCX-mini. The op-amps used in the QCX-mini are OPA2277 but they seem to be very expensive. It was suggested on the QRP Labs Groups.io reflector that an NE5532 would be equally acceptable in the later stages of the receiver chain. By chance I happen to have some NE5532 chips.
Today I swapped out IC9 and my radio is now working fine. I’m seeing 4.6 watts output on 30m from a 12v supply (idiot diode in circuit), so I’m happy with that.
I will have a fiddle with the windings and see if I can tweak it a bit.
(yet !) .
