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+--- Thread: Signal source for 23cm (/thread-630.html)
Signal source for 23cm - VK4WDM - 11-09-2018
I need a signal source for 23cm so I can continue to work on my evolving setup when the local beacon is off air. Anybody got a fairly simple circuit? I would also be open to buying a unit if somebody has a spare one.
73
Wayne VK4WDM
RE: Signal source for 23cm - VK5ZD - 11-09-2018
Feed the output of a 70cm transmitter via a suitable attenuator to a diode (a 1N4148 will do) and it will generate some 3rd harmonic (plus others).
RE: Signal source for 23cm - OZ2M - 12-09-2018
Hi Wayne
Here is one really cheap and handy way to do it: http://rudius.net/oz2m/milli_beacon.htm
Bo
RE: Signal source for 23cm - VK2KRR - 12-09-2018
I Wayne, I made one similar to what Bo has described with a 16 MHz oscillator and not as many other components, depends how stable you need it. I'd try searching google for designs using 16 MHz crystal. Cant remember where I got my info from. It works on 144, 432, 1296 maybe more.
I used mine to fine tune the location of the feed horn on my 12ft dish to minimise side lobes etc
RE: Signal source for 23cm - VK4ADC - 12-09-2018
Wayne
I have used a TTL oscillator for years in an almost identical arrangement to the OZ2M arrangement (though not using a PCB, just a 5V TO-72 style regulator + stabilisation bypasses on in/out, an output coupling capacitor & no diodes - rats nest style). My 16MHz oscillator was salvaged from a computer motherboard so is not a TCXO and as frequency stable as Bo's is.
The exact frequency is not critical as most radios will tune below 1296.0 if the oscillator is low of 16.000000 - as most I have encountered seem to be. Good for 2M & 70CM too.
Doug
RE: Signal source for 23cm - OZ2M - 12-09-2018
Hi
The secret indigence is not 16 MHz. It can be any frequency as long as the harmonics fall in the right place(s). Using a 48 MHz TCXO I have made it all the way to 10 GHz. So do the math on whichever TCXO you find. The "only" reason that 16 MHz is shown is that I had easy access to that frequency at the time of making the webpage.
GL
Bo
RE: Signal source for 23cm - VK4ADC - 12-09-2018
Bo
I still have rats-nest 16.000 test oscillator and I used it earlier this year when I did some 2M and 70CM yagi antenna pattern checks.
I also looked through all of the TTL oscillators in the junkbox quite a few years ago (>10), grabbed the best frequency assortment and mounted them onto a piece of Veroboard. The board was then mounted in a 'pre-loved' diecast box with a 10 position rotary switch that simply switched the +5V from the single regulator to the individual oscillators. Their outputs were commoned by individual 22pF capacitors to a single point and then to a BNC socket.
I wrote the frequencies on the box at the knob pointer but I had some useful frequencies that made the project worthwhile and they included 6, 8, 10, 12, 15, 16, 24, 36 and 50 MHz. Add the harmonic content and there are test signal frequencies all over the place. The 10th position was power off.
Like your project, the internal 9V battery works well with it and has a long battery life.
The moral is 'don't just chuck out old computer motherboards, I/O and video cards without removing the TTL oscillators'.
The newer style mostly-SMD boards are not as good a source of them...
Doug
RE: Signal source for 23cm - OZ2M - 13-09-2018
Sounds like a really neat solution Doug. I have used mine from a fixed point in the garden but also when on DXpedition where sometimes one can be in doubt if the RX still works.
One more thing. Some TCXOs exhibit more harmonics than others. So it is a good idea to try them all out. For this purpose using an IC socket may be a good idea.
Bo