Making FM from a Signal Generator and a Function Generator

[RedShoeRider]

Good Day, All:

I'm sure there's a good way....ok, I'm not sure there's a good way of doing this, but that's what askin' is for!

I recently got my hands on an Anritsu MG3670B Signal Generator for cheap. Lucky, that....300khz to 2.1ghz range, nice screen, but it's a Digital Modulation Signal Generator, so it can't make an FM or AM signal on its own. It makes a nice, clean sine wave, though.

Sitting next to it on the bench is a Tektronix AFG5101 function generator, good for DC to 12mhz.

So, the way I see it, I have a carrier generator (the Anritsu) and I have a signal generator (the Tek), but I have no idea what the easiest/most practial way of making the two of them work together to make an FM test signal is! I want a pretty broad range....anything from 2 or 3mhz up to 800 or so mhz for the carrier. I know it'll be an external box of some sort, but that's where I'm getting stuck. I'm happy for a DIY solution just the same as a commerical solution.


Thanks, all!
-Red

 

[betwixt]

I'm not familiar with either instrument but from your description you will have difficulty. The digital modulation is of no use to generate 'normal' FM and both instruments are tunable but not frequency modulatable. I would guess you need a further oscillator, one generating FM which you can then mix with the others to produce your desired frequency.

Brian.

 

[biff44]

that generator has an external I/Q modulation input. You could do small angle modulation of the carrier that way. As a crude example, just add a small sine wave at the I input, and have a small + DC voltage at the Q input, and you will have simple 50 to 130 degree modulator.

You could program a cheap Dual DDS to drive both I and Q to generate true FM.

You would have a low frequency phasor signal, fed into the I and Q that went clockwise, then stopped, then went counter clockwise, then stopped....i.e. FM constant envelope modulation

another cheap way would use an external 10 MHz VCXO at the reference input, and FM modulate it.