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Message |
chuck
Guest
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 Posted:
Thu May 19, 2005 12:35 am Post subject:
Tektronix 7L12 Spectrum Analyzer Question |
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I'm in the market for a used spectrum analyzer like the 7L12
or the HP 141-T. One important use will be to make two-tone
IMD measurements on HF SSB transmitters. I am concerned that
with tone separations on the order of one kHz, the 7L12 may
not have sufficient bandwidth in the 300 Hz mode to resolve
adjacent IMD products expected to differ in amplitude by 40
dB or more.
Has anyone on the group used a 7L12 for this purpose and is
the 300 Hz RBW sufficiently narrow?
There seems little doubt that the 141, with 10 Hz or 100 Hz
RBW, will handle this.
Many thanks in advance.
Chuck
NT3G
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John Miles
Guest
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| Posted:
Thu May 19, 2005 10:03 pm Post subject:
Re: Tektronix 7L12 Spectrum Analyzer Question |
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In article <428bad41_3@newsfeed.slurp.net>, chuck@nospam.net says...
| Quote: | I'm in the market for a used spectrum analyzer like the 7L12
or the HP 141-T. One important use will be to make two-tone
IMD measurements on HF SSB transmitters. I am concerned that
with tone separations on the order of one kHz, the 7L12 may
not have sufficient bandwidth in the 300 Hz mode to resolve
adjacent IMD products expected to differ in amplitude by 40
dB or more.
Has anyone on the group used a 7L12 for this purpose and is
the 300 Hz RBW sufficiently narrow?
There seems little doubt that the 141, with 10 Hz or 100 Hz
RBW, will handle this.
Many thanks in advance.
Chuck
NT3G
|
It wouldn't be ideal for 1 kHz spacing. If the -6 dB point is 300 Hz,
and the shape factor of the 7L12's filters is about 8:1 like other Tek
analyzers I've used, then the -60 dB point is around 2.5 kHz. Figuring
a linear falloff (in log space), 1 kHz tones couldn't be resolved below
about 30 dB, give or take 10 dB at the most.
I've never used a 7L12; maybe the filters are steeper than that. But
you can't beat an HP 141T / 8553B / 8552B (not -A!) combination for HF
work at less than 3x the price. If you've got the space, that's the way
you should go.
-- jm
------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
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chuck
Guest
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| Posted:
Fri May 20, 2005 5:30 am Post subject:
Re: Tektronix 7L12 Spectrum Analyzer Question |
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Thank you, John.
FWIW, Tek claims a 6/60 dB shape factor of "4:1 or less" at
all bandwidths on the 7L12. They're analog filters and after
30 years may not live up to their design specs. In the end
it strikes me as insufficient headroom for an instrument
requiring that kind of investment. I'll probably do the
right thing and find an HP 141-T.
Thanks again, John.
Chuck
John Miles wrote:
| Quote: | In article <428bad41_3@newsfeed.slurp.net>, chuck@nospam.net says...
I'm in the market for a used spectrum analyzer like the 7L12
or the HP 141-T. One important use will be to make two-tone
IMD measurements on HF SSB transmitters. I am concerned that
with tone separations on the order of one kHz, the 7L12 may
not have sufficient bandwidth in the 300 Hz mode to resolve
adjacent IMD products expected to differ in amplitude by 40
dB or more.
Has anyone on the group used a 7L12 for this purpose and is
the 300 Hz RBW sufficiently narrow?
There seems little doubt that the 141, with 10 Hz or 100 Hz
RBW, will handle this.
Many thanks in advance.
Chuck
NT3G
It wouldn't be ideal for 1 kHz spacing. If the -6 dB point is 300 Hz,
and the shape factor of the 7L12's filters is about 8:1 like other Tek
analyzers I've used, then the -60 dB point is around 2.5 kHz. Figuring
a linear falloff (in log space), 1 kHz tones couldn't be resolved below
about 30 dB, give or take 10 dB at the most.
I've never used a 7L12; maybe the filters are steeper than that. But
you can't beat an HP 141T / 8553B / 8552B (not -A!) combination for HF
work at less than 3x the price. If you've got the space, that's the way
you should go.
-- jm
------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------ |
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