I just acquired an HP 8640B and now I'd like to get rid of my HP 606A but I
need to go below 500 KHz. I wonder if anyone has had any experience with
the HP 11710A or B that they'd care to comment on. I'd also like to know if
there's any other reasonably priced LF sig gen that's stable and has a
calibrated output that I should consider as $150.00 for an HP 11710 seems
kind of high when you can find HP 8640Bs for around $200.
tnx
hank wd5jfr

I just acquired an HP 8640B and now I'd like to get rid of my HP 606A but I
need to go below 500 KHz.

Hank-

Recently someone mentioned that the 8640B was a UHF signal generator that had
digital dividers for lower frequencies. If that is true, you might be able to
add additional dividers to go lower in frequency. You might have to sacrifice
one of the existing bands, depending on how extensive the modification is.

73, Fred, K4DII

I just acquired an HP 8640B and now I'd like to get rid of my HP 606A but I
need to go below 500 KHz.

Hank-

Recently someone mentioned that the 8640B was a UHF signal generator that had
digital dividers for lower frequencies. If that is true, you might be able to
add additional dividers to go lower in frequency. You might have to sacrifice
one of the existing bands, depending on how extensive the modification is.

73, Fred, K4DII

To get lowband out of an 8640, I think I would simply add a mixer to the
output of the 8640.

Get a cheap oscillator, one of those computer time base ones, and feed it
into the LO of a double balanced mixer. SBL-1 or some such.

Feed the 8640 into the RF in and then you have your desired lowband on
the IF output.

==============

I'd add an attenuator to the IF output pin, 4 dB.

This way, assuming about 6 dB loss in the mixer, you know the output is
just about 10 dB below what the 8640 output level is and you can use that to
set the lowband output to a known level.


Jim Pennell
N6BIU

To get lowband out of an 8640, I think I would simply add a mixer to the
output of the 8640.

Get a cheap oscillator, one of those computer time base ones, and feed it
into the LO of a double balanced mixer. SBL-1 or some such.

Feed the 8640 into the RF in and then you have your desired lowband on
the IF output.

==============

I'd add an attenuator to the IF output pin, 4 dB.

This way, assuming about 6 dB loss in the mixer, you know the output is
just about 10 dB below what the 8640 output level is and you can use that to
set the lowband output to a known level.


Jim Pennell
N6BIU

I saw in the application notes for hp that for extending the range,they use
dividers with filters.
An other example was the use of the 5 MHz output as lo for a mixer.
Then use the generator in the range from 5 to 5.5 MHz and feed this also in
a mixer.

I saw in the application notes for hp that for extending the range,they use
dividers with filters.
An other example was the use of the 5 MHz output as lo for a mixer.
Then use the generator in the range from 5 to 5.5 MHz and feed this also in
a mixer.

(Fred McKenzie) wrote in message ...
I just acquired an HP 8640B and now I'd like to get rid of my HP 606A but I
need to go below 500 KHz.

Hank-

Recently someone mentioned that the 8640B was a UHF signal generator that had
digital dividers for lower frequencies. If that is true, you might be able to
add additional dividers to go lower in frequency. You might have to sacrifice
one of the existing bands, depending on how extensive the modification is.

73, Fred, K4DII

Yes, it uses digital divide-by-2 stages, but to get low harmonic
content in the output, the square wave is filtered by some pretty
decent filters. I don't know what the going price of things like the
HP3325A is, but that's a decent generator with very good frequency
resolution. For the low frequencies involved, you could also just use
a DDS, followed by a switched attenuator. A mixer down from higher
freqs is OK if you don't care about phase noise, I guess; add a LPF to
get rid of RF and LO feedthrough. You do miss one of the nice things
about the HP8640B, though, which is high output power. Getting back
to +20dBm with op amps shouldn't be too hard, but to keep SNR good,
you'd want to follow that with a step attenuator anyway (or take the
amplifier out of the circuit), probably, and not rely on just the 8640
output level to do the trick at really low levels.

Cheers,
Tom

(Fred McKenzie) wrote in message ...
I just acquired an HP 8640B and now I'd like to get rid of my HP 606A but I
need to go below 500 KHz.

Hank-

Recently someone mentioned that the 8640B was a UHF signal generator that had
digital dividers for lower frequencies. If that is true, you might be able to
add additional dividers to go lower in frequency. You might have to sacrifice
one of the existing bands, depending on how extensive the modification is.

73, Fred, K4DII

Yes, it uses digital divide-by-2 stages, but to get low harmonic
content in the output, the square wave is filtered by some pretty
decent filters. I don't know what the going price of things like the
HP3325A is, but that's a decent generator with very good frequency
resolution. For the low frequencies involved, you could also just use
a DDS, followed by a switched attenuator. A mixer down from higher
freqs is OK if you don't care about phase noise, I guess; add a LPF to
get rid of RF and LO feedthrough. You do miss one of the nice things
about the HP8640B, though, which is high output power. Getting back
to +20dBm with op amps shouldn't be too hard, but to keep SNR good,
you'd want to follow that with a step attenuator anyway (or take the
amplifier out of the circuit), probably, and not rely on just the 8640
output level to do the trick at really low levels.

Cheers,
Tom

HP made a downconverter for the 8640B. It's the 11710B.

- Jeff, WA6AHL