Topics

#mods #pa #80m #160m #160m #pa #mods #80m


Richard Hall
 

Please forgive me, Hans, I have desecrated your lovely work of art.
This PA was botched beyond redemption. I shorted the pads of Q1 and could not resolve the short even with Q1 removed. But your amazing T/R circuitry was intact and I needed a T/R switch so...
This mod seems to work. It even does QSK. Do you think it will destroy my QCX?
Suggested mod: Something similar could be done with a (not botched) PA. Just interrupt the circuit at C16 and add a BNC for the receive antenna.
Suggested kit: an outboard T/R switch using the same pin-diode circuitry with maybe a pass through for the PTT signal to key a following PA. This would be especially useful for the lower bands. One of the few high-end features missing from QCX is provision for a receive antenna.
Richard NS3C


Ryan Flowers
 

My own suggestion would be to document it much like the QCX-SSB hack. The kit is low enough priced that buying it just for this purpose is totally feasible :-) 

Ryan Flowers



On Mon, May 11, 2020 at 5:12 PM Richard Hall <n76003@...> wrote:
Please forgive me, Hans, I have desecrated your lovely work of art.
This PA was botched beyond redemption. I shorted the pads of Q1 and could not resolve the short even with Q1 removed. But your amazing T/R circuitry was intact and I needed a T/R switch so...
This mod seems to work. It even does QSK. Do you think it will destroy my QCX?
Suggested mod: Something similar could be done with a (not botched) PA. Just interrupt the circuit at C16 and add a BNC for the receive antenna.
Suggested kit: an outboard T/R switch using the same pin-diode circuitry with maybe a pass through for the PTT signal to key a following PA. This would be especially useful for the lower bands. One of the few high-end features missing from QCX is provision for a receive antenna.
Richard NS3C


--
Ryan Flowers - W7RLF
MiscDotGeek - QRP and More


Richard Hall
 

The purpose of this mod is to give QCX access to a receive-only antenna via the 50 Watt PA kit. This can be added to a functioning PA or the kit can be built as a T/R switch without the amplifier circuitry. The first approach is more elegant; the second, more broadly useful.
To add a receive-only input to an existing 50 Watt PA, desolder and expose the pin of C16 nearest C17. Solder a wire from that pin to the center connector of a BNC connector. Ground the BNC wherever is convenient and you're done.
To build the PA kit as a T/R switch only, omit everything from C3 to C15 on the schematic and run jumpers from C3 to C8 and C15. The through holes for R2 and R3 nearest C3 would be a good origin for the jumpers and they could end at the holes for C21 and C9. Then install a BNC as above, jumpered from C16. This version is band agnostic. The jumper to C8 is not shown in the photograph because I hadn't thought of it at the time the photo was taken.