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Question Tek 7L12 Spectrum Analyzer



 
 
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  #11  
Old May 20th 05, 05:50 PM
Randy or Sherry Guttery
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Chuck Harris wrote:

(flame suit on, helmet latched, as I await the onslot of rebuttles from
HP guys..)


No, I agree - while ok for "routine work" the 141 is *old*. OTHO - if I
were to suggest a Tek 7603 solution - I'd say see if you can possibly
squeak into a 7L18. I know - an absolute budget buster - but it can
"look" at just about anything in the "usual" spectrum - and do it with
fair accuracy. Had the pleasure of using them - never could afford one
myself - but perhaps some day. Oh - and a word of caution - if you're
going to some 7000 series solution like this - don't make the mistake of
buying an USM-281C - they'll tell you it's a 7603 - and indeed they are
- what they DON'T tell you is that they are a 7603 Option something or
other - which means they DON'T have the on screen readout... Which makes
a 7L - and similar stuff useless in them.

best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com
  #12  
Old May 20th 05, 06:52 PM
Chuck Harris
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Randy or Sherry Guttery wrote:
Chuck Harris wrote:

(flame suit on, helmet latched, as I await the onslot of rebuttles
from HP guys..)



No, I agree - while ok for "routine work" the 141 is *old*. OTHO - if I
were to suggest a Tek 7603 solution - I'd say see if you can possibly
squeak into a 7L18. I know - an absolute budget buster - but it can
"look" at just about anything in the "usual" spectrum - and do it with
fair accuracy. Had the pleasure of using them - never could afford one
myself - but perhaps some day. Oh - and a word of caution - if you're
going to some 7000 series solution like this - don't make the mistake of
buying an USM-281C - they'll tell you it's a 7603 - and indeed they are
- what they DON'T tell you is that they are a 7603 Option something or
other - which means they DON'T have the on screen readout... Which makes
a 7L - and similar stuff useless in them.

best regards...


I too, like the 7L18. I have the 7L5, 7L13, and 7L18 on my bench. The
7L18 is not a general purpose SA, as its range is 1.5GHz to 60GHz. It
doesn't go down to DC in its capabilities.

The 7L5 is DC to 5GHz, with digital storage.
The 7L13 is DC to 1.8GHz no storage.
The 7L14 is DC to 2.5GHz(?), with digital storage.
The 7L18 is 1.5GHz to 18GHz, 60GHz w/external mixers, with digital storage.

The 7L14 is the holy grail of the series, as it has the digital storage
and a slightly improved bandwidth.

They all make extensive use of the "labeling" feature of the 7000 series
scopes, so it is important to avoid the "N" option on your mainframe.

-Chuck Harris
  #13  
Old May 20th 05, 07:13 PM
Wes Stewart
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On Fri, 20 May 2005 11:57:37 -0400, Chuck Harris
wrote:


No, your data sheet is wrong. The slowest automatic sweep is 10 secs per
division. The slowest sweep is manual. This specification exists across
the entire 7L line.



That's not what this says:

http://www.tucker.com/images/images_spec/00000453.pdf


I pulled out a 1981 Tek catalog, and I am indeed remembering wrong.
This is yet another reason why I discounted the 7L12 as a credible SA.

Here is what Tek is expecting you to do. There are timebase positions
for 5ms through 0.01us. These are for use when the SA is being used as
a receiver (time domain mode), and you are looking at a received pulse
train.

The "SA" mode is *variable* from 10ms through 5ms/division. You are expected
to manually adjust the sweep rate to get a clear picture.

So, how can you get 300Hz filter resolution? Well, simply by not scanning
the full bandwidth of the SA plugin. Reduce the sweept bandwidth to 10KHz,
and 300Hz is easily achieved with a 5-10ms/division sweep rate. Not a great
way to go, but usually if you are interested in the narrow resolutions, you
are only looking for signals over a narrow bandwidth.


Well, you can always just use an hf receiver with a stepped attenuator
and a narrow CW filter, but it's not so handy.


As I said earlier, get a 7L13, or 7L14. The 7L12 wasn't fully incubated
when it was hatched.

When you go looking at the 141T, remember, it is a mid 1960's SA design,
and it feels like it when you use it.


Hey, if you started using SA's in the 60's it's perfectly natural. [g]
We had one (don't remember the no.) that predated the 141's. Two
boxes that took up about three feet of rack space. Drifted like crazy
and used harmonic mixing so you didn't know what the hell you were
looking at.


The 7L5, 7L13, and up were designed in the
very late 1970s, and take advantage of things like microprocessors to help
with house keeping operations. They are smaller, quite reliable, and just
plain work better than the 141T family. (And, yes I have owned, used and
repaired both.) The 141T storage tube is a nightmare. Very short life.


Not when used properly, which most weren't. The ones in my lab worked
flawlessly until we upgraded. I auditioned a TEK 492P when they were
first issued. Never liked it even tho I had a capital acquistion
approval for it I didn't buy it. Bought an HP8566 instead. Of course
there was no comparison size and weight wise, but the HP was
rack-mounted and wasn't going anywhere. Programming was *much*
friendlier.


Another SA line that is usually very inexpensive, and much better than the 141T
family, is the Eaton/Ailtech 727 and up. I was told (in the early '80s) by an
HP FAE (who specialized in HP's SA's and other RF gear) that the Ailtechs were all
over the place in HP's internal R&D labs. They were the SA's that HP used in
designing their own product line.


My only Ailtech experience was with their NF boxes and that goes back
to when we were using gas tubes in waveguide [g].

(flame suit on, helmet latched, as I await the onslot of rebuttles from HP guys..)


No offense to Roy Lewallen and Wes Hayward, but at Hughes it was an
unwritten rule, you want a 'scope, buy Tek; you want a network or
spectrum analyzer, buy HP. You want a DMM, "If it works, it's a
Fluke." I did buy a Wiltron scalar network analyzer once for a
dedicated test position.

If I was to have a SA at home just for hf work I would love an HP3585.

And until the N2PK network analyzer came along, I lusted for an
HP3577.

http://users.adelphia.net/~n2pk/index.html#TR
  #14  
Old May 20th 05, 07:14 PM
Randy or Sherry Guttery
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Chuck Harris wrote:


I too, like the 7L18. I have the 7L5, 7L13, and 7L18 on my bench. The
7L18 is not a general purpose SA, as its range is 1.5GHz to 60GHz. It
doesn't go down to DC in its capabilities.


Hmm. Quite right - I must be thinking about the 7L14 - as we weren't
doing anything that high - but at the time - whatever it was- was the
top of the line and brand new - as the Tek techrep hand carried it to
us. Like I said - got to use one - didn't get to keep it.

best regards..
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com
  #15  
Old May 20th 05, 07:43 PM
Chuck Harris
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Posts: n/a
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Wes Stewart wrote:

Hey, if you started using SA's in the 60's it's perfectly natural. [g]
We had one (don't remember the no.) that predated the 141's. Two
boxes that took up about three feet of rack space. Drifted like crazy
and used harmonic mixing so you didn't know what the hell you were
looking at.


I remember using one of those. It had the 140S display unit, a point contact
diode in the unbalanced mixer. The diode was under a cap on the front panel,
so you could tap it to improve its sensitivity, or replace it. Hot stuff
once. Hard to believe that anyone could get useful work out of one. I had
an Ailtech 707 in the same lab, you can guess which one got used.

The Ailtech was nice because other than the logging amplifiers, and the display,
there was nothing custom in the unit. It was a collection of microwave modules,
dbm's, yig vco's, ... all tied together with 141 semirigid hardline.

-Chuck
  #16  
Old May 26th 05, 02:28 AM
Steven Swift
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Have a look at the 7L14, it goes to 30Hz RBW.

chuck writes:

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

--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA
 




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