[time-nuts] OT favorite signal generator?

John Ackermann N8UR jra at febo.com
Fri Jun 19 10:42:43 EDT 2009


I took a look at the phase noise of a 3325B and as Jim said, the phase 
noise is not great -- about -60 dBc at 1 Hz offset.  An external 
reference cleans up the close in (<10 Hz) signal, but beyond about 10 Hz 
the synthesizer noice drowns out the reference; from the noise from 10 
Hz to about 3 kHz is about -115 dBc, then it drops off to a floor of 
around -135 dBc at 100 kHz.  Some plots are at 
http://www.febo.com/pages/hp3325b/

That said, they are awfully nice boxes for audio and low HF use.

John
----

Lux, James P wrote:
> We use a lot of 3325As in the lab at JPL (they used to have dozens of them at the deep space network, so there are lots of them around).  Some have the rear panel option that puts out a sine wave up to 60MHz, which is fairly convenient.
> The settability with lots o' digits is nice (that's why they were used in DSN..).. Really a function generator with sine square triangle, and some modulation capability. You can also lock multiple 3325s together which is nice for generating things like I/Q signals with known errors in phase/amplitude, or with frequencies offset by 0.1 Hz (so it sweeps through all relative phases in 10 seconds), or clock signals with known skew (although something like an 8110 or it's newer brethren is nicer).
> They're not super quiet
> 
> Depending on your needs, there might be better solutions.  For a bit more money($600), you can get the TAPR Vector Network Analyzer from TenTec, which has a calibrated signal generator mode.  In the few hundred dollar range, I've used a lot of eval boards from one source or another.  Analog Devices has a whole bunch of DDS eval boards that take an external reference (always important for timenuts use) and with a small amount of work, you can calibrate them. National Semi has a whole bunch of PLL eval boards, if you need GHz kinds of frequencies.
> 
> 
> On 6/19/09 6:13 AM, "Robert Darlington" <rdarlington at gmail.com> wrote:
> 
> I just bought an HP 3325A synthesizer/function generator that I really like
> (for some things anyway) in about that price range.   What you get is
> probably dependent on what YOU need though.  This thing is pretty limited
> but this particular one has the high voltage option so the output goes up to
> 40 volts up to 1MHz.   It only goes to 20.99999999 Mhz (at up to 10V I
> think) but for 99% of what I do that's just fine.  It has a 10MHz external
> reference which I hook to either an Rb osc or a Thunderbolt depending on
> what I'm doing.  It's pretty neat to see all the digits match between the
> 3325A and the 5335A counter.  Of course, that's being clocked by the same
> oscillator too.
> 
> Also, I noticed on some signal generators, dropping the output down to a few
> mV distorts the signal.  What I learned to do was send my signal out at
> about 1 volt ((RMS or p2p, doesn't matter) and go through a step attenuator
> to drop it back down so it comes out clean.
> 
> -Bob, N3XKB
> 
> On Fri, Jun 19, 2009 at 6:04 AM, Patrick <optomatic at rogers.com> wrote:
> 
>> Hey everyone
>>
>> Sorry for the off topic post. I have received great advice in the past
>> with items for my little shop and I can't resist to ask again.
>>
>> I am thinking about buying a signal generator. I suspect that I will
>> mostly use it to inject low uV/mV signals into the amplification stages
>> of the laboratory instruments I service.
>>
>> Any feedback you have would be greatly appreciated-Patrick
>>
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