When I got my Hilltpper 20, it was pre-built by an experienced QRP builder and QRP operator, so I was satisfied with it bveing built correctly. I ran it through the calibration process per the documents and was very satisfied with the results of that calibration. I had some trouble getting it exactly right so I was asking about the process on the 4 States QRP Group reflector. Dave Benson K1SWL, the designer of the Hilltopper rigs and former owner of Small Wonder Labs was kind enough to send me explicit instructions on the calibration process, and using those instructions I was able to get the transmit and the receive spot on.
So since I had Dave's attention, I sent him an email asking if there were any tweaks I could make to the receiver that would make it a bit louder and not sound so muffled or narrow. He responded that he'd been thinking about that and suggested I change R5 to 470K or 510K and change C22 to 150pf . He had calculated this might add nearly a 10db gain to the circuit.
R5 WAS a 150K resistor and C22 WAS a 470pf COG capacitor. They are located just above the Dual Low Noise Op Amp U3 which is a NE5532. See below:
|Swap R5 and C22 out with new values|
|Location of Parts to Swap out on Hilltopper 20|
Once I got the parts it took me maybe an hour total to remove the old parts and install the new parts. My de-soldering skills are horrid so I went slow so I didn't gronk up the circuit board. Solder wick is your best friend here, and having a de-soldering bulb handy is really really helpful.
I don't have any gear that I can use to measure the actual electrical improvement but my ears were VERY happy to hear an increase in audio gain, and an increase in the number of signals. I would tune a station on my K2 and then switch to the HT20 and was able to tune the same, even the weak ones.
Dave did mention that this mod MIGHT cause some screeching if I tuned any really loud signals, so far I have not experienced that. I reported the improvements to Dave and he is now working on a possible Op Amp replacement idea. I can't wait to see how that turns out. Stay tuned. If you perform this modification, please let Dave Benson know how it turned out for you and if you see any improvement. I was very happy with it.
Yesterday here in the Hoosier Heartland we had gorgeous sunny skies, fair winds, but cold temps. So I did not get to take the rig to the outdoors. Woke up this morning with a serious head cold and about an inch of new snow....good grief. Will Old Man Winter just pack up and GO.
73 de KB9BVN