Signal generator?

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Daniel Smith:
Can you point me to a good make and model?


Dale Hunt:
What frequency range do you want to cover?  How accurate does the frequency
need to be?  Do you need FM modulation, or is AM adequate?  Or something more
elaborate?  How accurate does the output level need to be?

The old HP-608 comes in several variants.  Seems to me the one I had worked from
10 to 400 MHz, so I had to use a converter to cover 80m and 40m.  Big, heavy,
analog readout, and lots of tubes.

Low end frequency range becomes important for IF stages (especially 50kHz or 70kHz).
High end has to cover your bands of interest.  Some of the cheaper ones have an extra
set of markings on the dial for the 3rd harmonic of the upper band - it looks like they
go higher than they actually do.  (While there will be some RF at the marked frequency,
there will be more at the fundamental.)  This may work OK with loose coupling, but runs
the risk of overloading the receiver with the fundamental.

For a lot of ham work, one of the simple tunable oscillators is often adequate.  I'm even
thinking of building my own that tunes, say, 3 - 15 MHz in a small package due to limited
space on my bench.  The current HP 8656B is great for 100kHz to 990 MHz, but it is
18" wide x 21" deep x 6" high, which doesn't leave a lot of room for other equipment.

The old Wavetek is still out in the garage - it does most of what I need to do in less than
half the size of the 8656, but requires repair every couple of years.  Fortunately a friend
has a couple more, so we can usually narrow down the problem by swapping modules
around, but I'd rather spend my time on other projects.

Peter Chadwick:
Depends what you want it for and how much you want to spend. I like the old HP8640B, but you need the internal multiplier to go up to 1GHz and the external mixer to go below 500kHz.

Daniel Smith:
It would be nice if it would go from (nearly) DC to 30 MHz but if the high end is 5 MHz that would be a nice start.  I need audio frequency coverage.  I may have to get a second unit later.

Dale Hunt:
Usually you don't find audio and RF in the same generator because the oscillator
circuits are different (not to mention the required bandwidth of any amplifiers, etc.)
Audio circuits often use an RC oscillators, tuned with a variable resistance, while
RF boxes are generally LC oscillators with switched inductance and a variable capacitor.

Synthesized boxes can have a lot more flexibility, of course, but still you'll generally
find separate "function generators" for audio (perhaps 1Hz to 50kHz) and RF (100kHz
and up).


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