I have discovered interesting synthesizer modules on eBay:
I have also found an interesting project from Alain, F1CJN on the Internet.
This synthesizer can easily be controlled by Arduino Uno and a Shield with LCD Display:
Final result is here. A synthesizer that can be programmed for many stored frequencies. Following picture shows one of them:
I will upload more about this wonderful synthesizer shortly. Hoping to use it for a small local beacon for 23cm.
Nothing is perfect. Not even synthesizers. There is a serious problem with spectrum purity when used for frequencies above ~ 1.1GHz. See following pictures.
We need 960MHz reference signal for a Microsource YIG that generates 23GHz. Spectrum around 960MHz seems to be OK:
However, 1296MHz seems to have a problem with spurious signal only 25MHz away and only 39dB suppressed:
Workable solution seems to be to generate the beacon signal on 1/2 frequency and double it. That would require 648MHz. Following picture shows reasonably clean spectrum for that. You can see the 2nd harmonic on the spectrum analyzer already:
Looks like I have to work on frequency locking in my lab - frequencies shown on my RIGOL analyzer are little off the frequencies shown on the Arduino. Luckily, this synthesizer allows (wonder of all wonders) locking to a 10MHz reference!
(to be continued)
I have retrieved my old 23cm filter that I built long time ago with the idea of using Flex 1500 with IF between 28 and 50MHz in mind. This filter was made per W6PQL description and is described incl. pictures and frequency response in my other posting here.
Wonder of all wonders, it fixed the problem! The 1296MHz signal is a little weaker (6-7dBm) but all unwanted peaks seem to be suppressed more than 55dB: