1.280GHz Signal Generator

[0utsider89]

I want to make a cheap 1.280Ghz or 1.240Ghz  Signal Generator.

My idea is to use a SAW resonator at 640mhz in combination with a x2 multiplier to generate the 1.280Ghz signal.
Or a SAW resonator at 310MHz, with a x4 multiplier to generate a 1.240Ghz signal.

RP1105 - 640mhz, looks like you can get them.
B39311R884H210 - 310mhz

The signal generator will be used as a test bed for making amateur radio fast scan TV signals with a mixer.

Thanks,
KJ6ICA

[KJDS]

If you have a 10MHz reference available, then I'd use a couple of these divide by 2 to 32

http://www.hittite.com/products/view.html/view/HMC394LP4

and an off the shelf VCO and make up a phase locked loop. That way you know it will stay on frequency.

[marshallh]

http://www.analog.com/en/rfif-components/pll-synthesizersvcos/adf4350/products/product.html

[0utsider89]

http://www.analog.com/en/rfif-components/pll-synthesizersvcos/adf4350/products/product.html

For the price that's not bad at all.  I'm thinking about get the Evaluation Board and do some testing, and then build my own board.

Thanks,

[Marco]

Ebay has some hobbyist frequency generators using the same chip BTW.

http://www.ebay.com/itm/RF-Signal-Generator-35MHz-to-4-4GHz-via-USB-15dBm-and-Features/200952667420

According to him it's an improved version of another design, presumably this one.

http://www.ebay.com/itm/4-4GHz-PLL-RF-Signal-Generator-Synthesizer-via-USB-/120923927269

[nctnico]

The problem with these generators is that they output lots of 2nd and third order harmonics (the output is a square wave). The seller cleverly hides that fact by showing a limited span.

[fcb]

I'd roll my own varactor based VCO and then use something like an ADF4107 PLL to hold it.

Much lower 2nd/3rd harmonics (easier to filter) than using a divided down generator.

Have you got an SA?

[0utsider89]

I'd roll my own varactor based VCO and then use something like an ADF4107 PLL to hold it.

Much lower 2nd/3rd harmonics (easier to filter) than using a divided down generator.

Have you got an SA?

I have a spectrum analyzer that covers the band.

That idea would work, but it could be a lot harder to build up. Its not easy to make a osc at 1.2ghz. I could be wrong though, I have not done a lot of RF design in the 1.2ghz band.

Thanks

[0utsider89]

And too add to that last idea it would be cheaper / easier, just to add a filter to the output of the adf4350 VCO/PLL, if I was really worry about the 2nd and 3th order harmonics. Witch in a lot of casts, would not be a problem since the 2nd order harmonic would not be passed by the antenna, and the 3th order harmonic would be so low in power, that it would not really be much of a problem.

At most my final out power is going to be around 350mW.

[fcb]

The ADF4350 is 2-3x the price of the ADF4107 (which is quite an expensive part anyway) - only you know your budget.  If your building a one-off, then it's cheaper to buy an RF sign gen (depending on how you cost your time).

A little colpitts oscillator is straightforward to build, Alpha appnote APN1006 might help.  And tuning for low 2/3rd is relatively easy - depends on what specs you have to meet, and how much you can get rid of in your PA.

[PA4TIM]

I made a signal generator that does 25-2000 MHz. I used VCO's from minicircuits.
http://www.pa4tim.nl/?p=2662 for pictures. It is not ready yet. I must build the powersupply in the cabinet but I have allready tested it with the temporary psu.
You can buy a development kit direct from MC . That is much cheaper then the separate VCOPs