A VEC in Idaho, contacted me following yesterday's posting and it seems a YL there passed the Tech, General and Extra, all in the span of 45 minutes. So that sounds like the record. Hopefully today she is the Chief Designer at a US Manufacturer of SDR Ham Gear. Congratulations for the accomplishment.
More radios I found stashed away and our feature for today has an interesting pedigree and history. About 10 years ago myself and KK6FUT, now AI6YR, created a multipart project and several articles for QRP Quarterly. The project was called LBS... Let's Build Something. The project started as a 40M DCR and evolved into a complete 40M SSB transceiver. Subsequently I built a stand-alone version for 20M that extensively used SMD components. This last element of the project involved a very complex engineering solution... read on!
This design was hailed as a DifX... something different than a Bitx and advanced features like a 10 second 988Hz Pulsed Tone for tune up and small size for portable operation. The SMD IF Module was based on the Plessey PNP/NPN Complementary Circuit. The 9 MHz 4-pole crystal Filter was purchased from INRAD. Zin/out = 200 Ohms, a 4:1 match to 50 Ohms.
Complex Engineering Solution
To have a complex solution follows a complex problem. Long ago I discovered that you could purchase galvanized sheet metal stock from Home Depot. It is sold in small sheets about the size of typing paper and is cheap. Having a tabletop metal brake, making cabinets out of this material is a breeze and cost effective. This material is also a problem!
The galvanized metal cuts easily with hand tools, can be painted and even soldered to other metals or metalized surfaces like PC Board. It is also magnetic.
There are old wife's tales about our beloved toroid inductors being self-shielding akin to all blond YL's are polyamorous. So, my complex problem... and the solution.
The Band Pass Filter was located on the top board (of two PCB's) at the very back end of the board and close to the back panel of the cover enclosure.
In practice I would align the BPF and get a strong signal output on 20M of about 5 watts PEP. The alignment would occur with the case cover off. Put the cover on and the received and transmitted signals would drop off like over a cliff. Our galvanized (and magnetic) metal cover, when in place, was detuning the BPF.
This certainly cast a pall about toroid self-shielding but at this point uncertainty about the blond theory. In all fairness the trimmer capacitors may also be subject to de-tuning, and the blond set might be expanded to include redheads. Nonetheless, the BPF was being impacted.
Two possible solutions came out of a brain farting session. One solution was to cut holes in the top of the cabinet aligned with the trimmer locations. The theory was "put the cover in-place and tune the trimmers".
The second approach was to address the detuning with the cover off. This by far is the better solution than the 1st Brain Fart. With adjustments made with the cover in place when doing any routine maintenance, if the cover is off the BPF is detuned.
Coming up with a fix so that the BPF is in tune with cover on or off is the goal and that was achieved with a piece of scrap metal.
A piece of the scrap galvanized metal was butted up to the BPF and soldered to the copper PCB and the BPF was TFMS (Tuned for Max Smoke). Now the BPF is correct for case on or case off.
This is a true example of when you know stuff you can do stuff. I do wonder however if our 45 Minute Extra could come up with an LBS project or a complex solution to the BPF problem. BTW the original LBS was built on a 3 foot by 3-foot chunk of plywood and so there was indeed a shrink down in size for the 20M version.
73's
Pete N6QW