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HP8640B-opt323: Should I return it?
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Ice-Tea:

--- Quote from: tatel on June 27, 2023, 08:27:56 am ---One last thing: I was expecting output level be the same on all the frequencies, as long as output level knob remains in the same position. However output level varies with frequency. Is that the usual behaviour?

--- End quote ---

Depends on how much it varies. If it varies by 1-2dBm then that is to be expected, especially for an old, uncalibrated and unadjusted device.
tatel:
EDIT: I messed seriusly these measurements.

I would say it varies quite a bit more than 1-2 dBm.

As said, I'm measuring with oscilloscope probe on N connector pin, short ground spring to N connector sleeve, 50 ohm pass-through terminator on oscilloscope input. Frequencies are in all cases in the middle of the range. Last one could be attenuated since it's near oscilloscope's -3 dB limit. These are the results:

.5   -    1 MHz ---------------------->      52 mVrms
1    -    2   "    ---------------------->    102     "
2    -    4   "    ---------------------->    200     "
4    -    8   "    ---------------------->    368     "
8    -  16   "    ---------------------->    616     "
16  -  32   "    ---------------------->    906     "
32  -  64   "    ----------------------> 1.26    Vrms
64  - 128  "    ----------------------> 1.21       "     

Maybe it could be adjusted. We have an organization of pirate FM stations and there could be a power meter sleeping somewhere. Or perhaps this is a red flag and device should be returned ipso facto.
Ice-Tea:
What do you mean 50ohm termination on scope input?
tatel:
Oops... your comment made me realize that I seriously messed up my measurements, not just because I used terminators, but because probes were on 10x attenuation. Sure enough, with probes on 1x, no termination, I'm getting about 2.25-2.35Vrms on all ranges (I mean the lower ones, up to 20 MHz which is the BW of my best probe on 1x).

I expect the N-to-BNC adapter will be here this week. Then I will measure all ranges up to 100 MHz with coax cable. I guess I'll be unable to understand the meter until then.

What a wonderfully helping resource this forum is. Thank you very much.

EDIT: Distortion on the 32-64 MHz range is now missing. I suspected I was having some reflection but it should have made me thinking again about my "measurements"
tatel:
Adapter arrived. So I measured output levels again. N-BNC adapter, 50 ohm coax, 50 ohm terminator, oscilloscope.

Output levels seem to be mostly right. Yeah, generator meter has to be read on the 0-3 and 0-10 scales, depending on the position of the output knob. If it has some kind of "3" mark on the inner circle, 0-3 scale has to be used. If it's a "1" mark, 0-10 scale is used instead. No fancy light indicators.

Output is basically the same on all frequency ranges as long as output knob remains untouched. On 48 MHz and above I see generator meter maxes out on the 1 volt output level range. However I read lower and lower values. Surely enough the reason is oscilloscope bandwidth.

Lectures are flat up to 24 MHz, then at 49 MHz and above they get lower and lower. Oscilloscope (GW Instek GDS1054B, upgraded) -3 dB limit is at 109 MHz.  It nicely coincides with I was expecting form risetime (about 3.2ns) measured with Leo Bodnar's pulser.
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