I just finished building a QCX-mini for 10m.
I ended up with:
?
T1 T50-6 (yellow)
Primary: 4T
Secondary 1: 4T
Secondary 2: 4T
Secondary 3: 14T
?
L4 T37-6: 5T
L1 & L3 T37-6: 9T
L2 T37-6: 10T
On RX alignment, I can peak the BPF with the modified T1. Note that I swapped the supplied T1 T50-2 core for a T50-6. I also swapped supplied L4 T37-2 core for a T37-6.
On TX I get 5W out with supply of 14.4V (protection diode fitted).
So all good on TX. The only problem is that RX sensitivity a little low. Comparing it to my old Ten Tec Corsair 2, the QCX-mini is definitely a bit deaf and cannot hear weaker signals at all. I did read a post from Hans where he suggested power out on 10m may be lower and an RX pre-amp may be desireable.
Has anyone had the same issue with lower RX sensitivity on 10m? Has anyone got any suggestions for a pre-amp circuit? Alternatively, any suggestions for improving sensitivity?
If I go down the pre-amp route, I am thinking that an external amp with bypass on TX could be tried. I could get 5V power and T/R switching for the pre-amp from the PTT socket. Maybe a common gate FET pre-amp circuit could be used? I suspect that only 12dB of gain might be enough. As the QCX-mini is in the little QRP enclosure, it might be a struggle fitting an amp inside. Hence, the thinking to go for the external option.
Despite the low RX sensitivity, I have made a few QSOs and, as with the other QCXs I have built, really enjoy using this rig. In fact, before I "tweaked" the various inductors as above, it was only putting out about 1.25W and I manged a couple of QSOs with NA ?.
GM0HUU Steve