Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
8970B Problem
开云体育Dear All,I have a problem with our 8970B Noise Figure Meter. It calibrates fine- no Errors indicated. However, after calibration with a direct through connection between noise source and instrument input, whilst the Gain shows 0dB +/- 0.05 dB, the Noise Figure shows down to around -0.3 dB at 1600 MHz. This is so, even on the exact frequencies where Cal. values from the Noise Source have been entered into the ENR table. I have tried 436A and 436B noise sources, including a recently delivered one, well within its calibration interval. Also noise sources from other manufacturers. All show about the same error after running calibration. Any suggestions as to what the problem might be? Thanks, Alwyn ?? _____________________________________________________ Alwyn Seeds, Director SynOptika Ltd., 114 Beaufort Street, London, SW3 6BU, England. Tel.: +44 (0) 20 7376 4110 SynOptika Ltd., Registered in England and Wales: No. 04606737 Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom. _____________________________________________________
|
|
Pete Manfre
When did you last do an IF cal.? ?Have noise sources been cal 'd Pete wa2odo On Thu, Feb 21, 2019, 5:06 PM alwyn.seeds1 <a.seeds@...> wrote:
|
|
What you describe is normal in my experience with the 8970 NF meters.???? This seems to occur when the frequency step and is out of kilter with the interpolation of the NF cal tables. If you want to improve the uncertainty, reduce to a smaller sweep centered around the frequency of interest, ie.? +/- 50 MHz with 10MHz steps. 73 Wayne ZL2BKC |
开云体育Dear Wayne,Thanks, but I am running the test on a single frequency- no sweep in use. In an attempt to avoid interpolation errors, I have also tried setting the frequency to be one of the frequencies that I have entered an ENR value for, but does not affect the result. -0.3 dB is rather a lot and a negative NF value disquiets. Regards, Alwyn What you describe is normal in my experience with the 8970 NF meters.???? This seems to occur when the frequency step and is out of kilter with the interpolation of the NF cal tables. If you want to improve the uncertainty, reduce to a smaller sweep centered around the frequency of interest, ie.? +/- 50 MHz with 10MHz steps. 73 Wayne ZL2BKC _____________________________________________________ Alwyn Seeds, Director 114 Beaufort Street (Management) Company Ltd., 114 Beaufort Street, London, SW3 6BU +44 020 7376 4110 114 Beaufort Street (Management) Company Ltd., Registered in England and Wales: No. 02797775 Registered Office Address: 114 Beaufort Street, London, SW3 6BU ______________________________________________________ |
开云体育Dear Pete, What procedure would you recommend for an IF cal.- I have the operating manual only? I suppose I was a bit puzzled by the insertion gain measuring 0 dB, but the NF measuring -ve. This meter has not been cal’d recently- I think Keysight still offer calibration- I can check. The noise sources include one with a current Keysight Cal. certificate and a precision one from G8FEK. All show the same result. All sources agree within their spec’d uncertainty when checked using an SA-based measurement system. By the way, permit me to say a good word for the G8FEK sources- very handy for NF measurements, meet their spec. and have a ?price-tag that amateurs can afford. I have no connection with Martyn, except as a satisfied customer. Thanks, Alwyn Date: Thu, 21 Feb 2019 15:16:12 PST? When did you last do an IF cal.? ?Have noise sources been cal 'd Pete wa2odo _____________________________________________________ Alwyn Seeds, Director SynOptika Ltd., 114 Beaufort Street, London, SW3 6BU, England. Tel.: +44 (0) 20 7376 4110 SynOptika Ltd., Registered in England and Wales: No. 04606737 Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom. _____________________________________________________
|
|
Dr. David Kirkby from Kirkby Microwave Ltd
On Thu, 21 Feb 2019, 22:06 alwyn.seeds1, <a.seeds@...> wrote:
IIRC there is an IF output on the rear. Have a look at that with a spectrum analyzer. I had an 8970B which showed stability issues.? Is the uncorrelated noise figure in spec? I believe its about 6-8 dB depending on frequency.? BTW, I believe someone has created a device that makes an 8970A/B show a negative noise figure by it having a negative input resistance.?
Dave? |
开云体育Alwyn,Do you have the pullout cards for the 8970B, in the tray under the instrument? IF calibration is Special Function 33.1 and requires a noise source with approximately 15db ENR. Steve On Feb 22, 2019, at 5:00 AM, alwyn.seeds1 <a.seeds@...> wrote:
|
开云体育Dear All,Many thanks for your advice, especially to “nj902” who pointed me to the explanation. I’ve now verified what happens as gain/NF of the measured object is changed and it is nice to find that this is not a fault. Regards, Alwyn From:?nj902 Date: Thu, 21 Feb 2019 21:22:23 PST? Apparently, this is normal. _____________________________________________________ Alwyn Seeds, Director SynOptika Ltd., 114 Beaufort Street, London, SW3 6BU, England. Tel.: +44 (0) 20 7376 4110 SynOptika Ltd., Registered in England and Wales: No. 04606737 Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom. _____________________________________________________
|
开云体育Dear Dave,Thanks. Yes, uncorrected NF is normal. The explanation proved to be that given in AN1484. So I’ve learned something, for which I am most grateful. Regards, Alwyn IIRC there is an IF output on the rear. Have a look at that with a spectrum analyzer. I had an 8970B which showed stability issues.? Is the uncorrelated noise figure in spec? I believe its about 6-8 dB depending on frequency.? BTW, I believe someone has created a device that makes an 8970A/B show a negative noise figure by it having a negative input resistance.? _____________________________________________________ Alwyn Seeds, Director 114 Beaufort Street (Management) Company Ltd., 114 Beaufort Street, London, SW3 6BU +44 020 7376 4110 114 Beaufort Street (Management) Company Ltd., Registered in England and Wales: No. 02797775 Registered Office Address: 114 Beaufort Street, London, SW3 6BU ______________________________________________________ |
开云体育Dear Steve,Thanks; yes I do, and I have suitable noise sources, so will run that. Regards, Alwyn Alwyn, Do you have the pullout cards for the 8970B, in the tray under the instrument? IF calibration is Special Function 33.1 and requires a noise source with approximately 15db ENR. Steve _____________________________________________________ Alwyn Seeds, Director SynOptika Ltd., 114 Beaufort Street, London, SW3 6BU, England. Tel.: +44 (0) 20 7376 4110 SynOptika Ltd., Registered in England and Wales: No. 04606737 Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom. _____________________________________________________
|
|
kevin kearns
?
toggle quoted message
Show quoted text
Got a link to AN1484?
?
Kevin
|
|
Hi Kevin, this is the link for AN1484 (and other info, manual, etc.): Dario IU3ARP ? Il 23 febbraio 2019 alle 7.53 kevin kearns <kkyahoo@...> ha scritto: ? ? |
|
kevin kearns
?
toggle quoted message
Show quoted text
Thanks Dario
|
|
kevin kearns
?
toggle quoted message
Show quoted text
Hi All,?
?
?Does anyone else notice that it takes longer?for
the NF reading to stabilize?compared with?the gain figure on the
8970B? When you calibrate the machine after a few minutes after switch on, gain
reads zero and is stable. NF will read zero straight after cal?but drifts a
bit, so it takes 10 mins warm up or so for the reading to?stay at zero
after cal.
?
Checking the machine with a precision 6.0 dB attenuator, Gain
reads 6.01dB and NF reads 6.10 dB when all warmed up.
Kevin
|
|
kevin kearns
?
toggle quoted message
Show quoted text
Gain reads -6.10db!
|
|
kevin kearns
?
toggle quoted message
Show quoted text
Sorry too early for me this morning!
?
Gain reads -6.01dB, got there in the end.
?
Kevin
|
开云体育More likely too much blood in your caffeine stream? My 8970B takes about 40 minutes to settle from a cold start but then it's fine. The time taken for the NF display to settle is affected by the value of the smoothing factor you've set of course. Adrian On 2/23/2019 8:20 AM, kevin kearns
wrote:
|
Dario
to navigate to use esc to dismiss