All of us have experienced a visit with an old friend. Most often it is like putting on a pair of old comfortable shoes. Your feet love them, and it just feels right. But you also note that the age factor has somehow entered the equation.
You know it is like that old girlfriend that at one time certainly had a "perky pair" but with the cruelty of the time factor are now simply a "dumpy duo". But it is the wiseman who realizes the big picture and not one single frame.
So, it is with homebrew radios that are over five years old. In 5 years, the technology has moved through two generations and what was leading edge is now the trailing edge; but that does not mean that old rig is still not useful.
The other day I pulled out a rig I built some five years ago, and this was like meeting an old friend. I find myself cycling through these old radios because either my antenna is broken or my prediction about Cycle 25 was correct.
Dismal is the propagation and overnight we have gone from a perky pair to a dumpy duo. In plain simple terms we have been sold a bill of goods about how great Cycle 25 will be. I heard several discussions about this just yesterday on 20M and so it is not just me or my antenna. Thus, a good time to look over past work as there is no propagation!
This particular rig was built for one purpose -- it was to test homebrew and commercial crystal filters. With about 3 minutes of work on the Arduino sketch a new filter frequency is accommodated. The only other chore is to install appropriate matching transformers.
But there are two other bonuses to this approach. The first is that the rig serves as a benchmark. The only thing changing is the filter so like a trip to the eye doctor is B better than A and the second is to test "odd ball" filter frequencies in a known test jig.
One homebrew filter sounded really great and then using my R4C I tuned across the passband and listened to the opposite sideband, and it was there. This told me that I had an issue with the filter itself and/or placement of the carrier oscillator on the filter slope. The R4C had a 1-inch antenna so the opposite sideband was really strong!
[Sidebar. Has anyone noticed that we don't hear much about Nano VNA's these days -- hmmm the novelty must have worn off and another whiz bang gadget is gathering dust at the end of a workbench.]
The rig is nothing special but does have some unique features. The Mic Amp was my 1st attempt to use a PNP transistor and the bilateral IF module is the Plessy circuit. The Driver stage uses the one out of EMRFD and I believe is much like a 13-year-old YL pretending to be 18.
I never ever did see the gain out of that stage like was predicted and there are about a half dozen of my transceivers that have that in the design. I have stopped using it. Just because it is in EMRFD does not mean it is the gold standard. Get over it as there are other designs.
40M at 5 AM
Typically, I see about 4 watts out of this radio with the IRF510 in the Final slot. I use the Half Moon Bay SDR receiver site as a listening post, and I was easily spotted 300 Miles away on 40M with an S7 signal level.
Them that know can make it go.
73's
Pete N6QW