Construction
The prototype was originally built on a bit of waste PCB, as in the photo at the top of this page. I took absolutely no time to make it neat as I only wanted to check the design before I laid out the PCB, so I offer absolutely no apologies for beauty. The PCB has been assembled for the VHF-HF transverter board, and it worked even better than the bird's-nest (that's unusual). I have laid out a PCB for this project.
The PCB itself measures 2.0" x 2.3" (51.5mm x 59mm), single-sided. The above drawing is 50% of the drawing scale but you can view and download the full-size hi-res PCB if you click on the picture above (opens in a new tab). If your graphic printing program (eg. PaintShop Pro) has a default of 72 pixels/inch (28.346 pixels/cm), then in the "Print setup" menu, set the print resolution to 24%. If there is a "Use printer resolution" option then select it. It will give you a 51.5mm x 59mm printout. The PCB was drawn in Proteus 7 Professional. The hi-res circuit board is 4x the normal size, so if you want to print it then do NOT resize the drawing or you will loose a lot of detail. You can alternatively import the picture into an MS-WORD document, switch ON the ruler and set the picture to the correct size to print to 100%.
Note that the text SM0VPO on the PCB copper side should be the correct way round when read from the copper-side.
The inductor L is wound using 0.8mm diameter enamelled wire on a 4mm diameter drill bit. Be sure the turns are very close-spaced; touching is best. It is worth taking a bit of time to get the coil exactly as you can see in the photograph. If you have difficulties getting below 90MHz then you can put a 4mm diameter ferrite bead in the coil. If you do this then you may will find the modulation sensitivity will increase. A coil this small and so few turns may not give you any microphony problems. If you do notice any microphony then a little blob of candle wax on the coil will stop it.
Note that most ceramic capacitors on the PCB have three holes printed. This is so that you can select either 2.5mm or 5mm lead spaced capacitors. The 10pf and 22pf capacitors should be NPO types (usually have a black painted spot at the top of them). The preset tuning capacitor (20pf) VC may be 2-pin or 3-pin types, and there is space on the board for either variant. You may have to increase the hole size to 1mm for some variable capacitors. The "Fine Tune" potentiometer RV is also generous with space so that you can have almost any miniature preset potentiometer.
As usual, stuff all the horisontal components first, then the vertical, and the transistors last. Fit the heatsink on TR2 before you power-up the transmitter. Check the supply has no short-circuits, and check that the emitter of TR2 is not shorted to ground. 2N2369 is a fantastic VHF transistor, but it is a bit unforgiving and easy to burn. Don't worry about that, "just look at the plumage" (google it ).
One little point that needs explanation is the one wire-link on the PCB, marked WLK/Test on the component overlay. This is the connection from the transmitter to the Low-Pass filter. For testing purposes, you can connect to either the transmitter output, or the filter input, before fitting the wire link.
Testing
Set RV to 50% and double-check there are no short circuits. Be sure that your two diodes are the correct way round.
Set your Power Supply Unit (PSU) to 6V DC and the current-limiting to 50mA. If you do not have a PSU with current limiting then use 4x AAA cells and an old pocket-lamp bulb, the ones with a tungsten fillament. If the lamp lights then you have a short. If not then you should get about +7dBm (5mW) out from the transmitter. Check the voltage at TR2 emitter is about 1V or somewhere around that.
If all is well then you can increase the voltage to 13.8V (slowly) and watch the output rise to around +23dBm (200mW) or more. Measure the voltage across the 9.1V Zener is in fact 9.1V DC. Now tune an FM receiver to around 105MHz, between any other stations. Adjust the variable capacitor VC slowly until you get a nice "thump" from the radio speaker, and a reduction of noise on the radio as you tune through it. Use the RV control to fine-set the frequecy to the radio. Connect the MP3-player (cassette player or gramophone, depending on how old you are) headphone output into the AF-in terminals. Adjust the MP3 player volume so the radio volume is about the same volume as other broadcast stations. If you really do want to broadcast Barry Manilow songs then you should set the modulation even lower - ±0kHz would be a good starting point .