Well, I've tried, but my stock is not up to snuff for this and I'm out of time.
Again, if the radio he is looking at is a modern radio, then it is almost certainly a "radio on a chip". If it is an older unit, say from the 60's or earlier 70's, then they would be mostly discrete components with coils, etc. And even then, the FM section is harder to hack. If he follows the antenna onto the board and finds an actual coil, and the actual tuner is an air-gap variable cap or a small plastic encased variable cap (old transistor radio type), then it's possible. See the coil I specify below.
Here are 2 very useful links for calculating the needs of the coil and variable cap:
Put in 2 values and it calcs the 3rd - https://www.omnicalculator.com/physics/ ... equency-LC
Plug in the dimensions and details and it calcs the value of the coil - https://www.electricaltechnology.org/20 ... lator.html
That being said, there are some possibilities that are unvetted. You may or may not wish to include them in your letter.
To start off, if the person can get a relative or friend to order the Baofeng listed above or another similar type, then that would be the best outcome.
I looked at a few stores:
Kohls has one for $20, regularly $25: https://www.kohls.com/product/prd-40132 ... d=60381826
Home Depot had one for $25: https://www.homedepot.com/p/Eton-Americ ... /310199899
There are still companies that accept real snail mail orders, so that might be an option too, but most want a lot more for their radios, the least expensive one I saw at Newark was around $80. Probably out of reach.
Now to the scratch builds. The requirements are pretty steep for this, using just 3 volts, and the fact that there is a shortage of small enough variable caps out there for the picking.
The first 2 are tutorials on how to make variable caps at home.
This uses cardboard forms: https://crystalradio.net/beginners3/cap.shtml
This one uses a screw and enameled wire: https://www.electronicproducts.com/Pass ... citor.aspx
Schematics - here's 2 that can be modded - a different coil should do the trick:
Just the receiver, it will need very high impedance earphone/earpiece (think crystal - good luck finding one) or an external amplifier: http://electronicseveryday.blogspot.com ... eiver.html
- replace the coil with 1/4"D x 5/8"L x 7 turns. That should get you in the ballpark with the specified tuning cap. For the BF199 transistor, possible substitutes would be 2N5109, BC547 or 2SC945.
Complete radio and amplifier with volume control but runs on 6 - 9 volts: https://electronicsprojectshub.com/fm-receiver-circuit/
- replace the coil with 1/4"D x 5/8"L x 7 turns, same as above. replacement for the BF494/BF495 is 2N3707, though a 2N3904 or 2N2222 might work.
Checking All Electronics, they have a lot of what is needed here, including variable cap, wire other components and protoboard. (1-800-826-5432) 14928 Oxnard St. Van Nuys CA, 91411-2610
Digikey, Mouser and Newark are other places that have even more than All Electronics, but I'll leave their info up to you.
Wish him good luck for us!