I was playing with our new spectrum analyzer and decided to just hang
a 12" cliplead off the input to see what was floating around.

See pics. The biggest signal was about -26 dBm, an FM station I guess.
Just about every slot on the FM band is full.

There's also some stuff around 1.9 GHz, but not as big.

This spectrum analyzer does a good job of confining its own LCD
backlight noise, but my TDS2012, right nearby, sure doesn't!

With a field like this, we could likely put a modest dipole on the
roof and get enough power to light an LED.


John

John Larkin wrote:
I was playing with our new spectrum analyzer and decided to just hang
a 12" cliplead off the input to see what was floating around.

See pics. The biggest signal was about -26 dBm, an FM station I guess.
Just about every slot on the FM band is full.

There's also some stuff around 1.9 GHz, but not as big.

This spectrum analyzer does a good job of confining its own LCD
backlight noise, but my TDS2012, right nearby, sure doesn't!

With a field like this, we could likely put a modest dipole on the
roof and get enough power to light an LED.


John


The rf field survey for your work area is a good thing to keep tack of.
Sometimes you add gain ad in the midst of a prototype odd signal begin
to be sen. well with the rich f environment at high huge power levels
will be "seen" on your low noise designs, way before ktb or shot noise
or just a bad front end...

Marc

John Larkin wrote:

I was playing with our new spectrum analyzer and decided to just hang
a 12" cliplead off the input to see what was floating around.

See pics. The biggest signal was about -26 dBm, an FM station I guess.
Just about every slot on the FM band is full.


Looks like a luxury analyzer. Aeroflex? I thought you could buy those
only with a GSA account or for government contract work.


There's also some stuff around 1.9 GHz, but not as big.


Could be DECT phones.


This spectrum analyzer does a good job of confining its own LCD
backlight noise, but my TDS2012, right nearby, sure doesn't!


Once I did EMC work for a client and their Agilent analyzer's flat panel
was self-polluting so badly I had to stop and buy some chimney spark
screen. Surprisingly they didn't have good old screen door stuff, only
the plastic variety. Should have taken a picture, with that screen the
analyzer looked like a Humvee going into battle.

IMHO the TDS series is a disgrace for Tektronix. That noise was the very
reason why I didn't buy one and chose the competition. But when they put
a measly 2.5K in there, what were they thinking? Now I've got 25K and
paid less 8-D


With a field like this, we could likely put a modest dipole on the
roof and get enough power to light an LED.


I've got one client next to an unmarked property with lots of huge
shortwave antennas on there. Oh man, that is tough to debug sensitive
analog gear in such an environment. Another is next to a busy airport, a
couple hundred yards from the runway. That noise session is planned for
some time in October and it'll be fun. The 9:45 just departed, quick,
lets do the scan ...

--
Regards, Joerg

http://www.analogconsultants.com

On Wed, 19 Sep 2007 00:17:53 GMT, Joerg
wrote:

John Larkin wrote:

I was playing with our new spectrum analyzer and decided to just hang
a 12" cliplead off the input to see what was floating around.

See pics. The biggest signal was about -26 dBm, an FM station I guess.
Just about every slot on the FM band is full.


Looks like a luxury analyzer. Aeroflex? I thought you could buy those
only with a GSA account or for government contract work.


It's the new 3 GHz Aeroflex; anybody can buy it. With all the options
(tracking gen, preamp, high resolution) it was $13K or something. It
has a few firmware bugs, but I think they're sincere about fixing
them. Except for a few glitches, it's a lovely box, with a beautiful
display.

I was disappointed in the harmonic distortion, -65 dB typically, but
it looks like that's actually not real bad compared to other units. We
have some RF signal generators that have THD numbers like 1.5%!

To test some amps we're doing, I guess we'll have to buy a few sets of
matched lowpass/highpass filters, so we can pump in a clean sinewave,
then and pull out the fundamental before we feed it to the spectrum
analyzer. What a nuisance. Maybe we should find/make a couple of
tunable notch filters.

How does one measure the THD of an amplifier, down around -70 dbC, in
the 1-30 MHz range maybe?

Why don't spectrum analyzers do log sweeps?

John

Le Tue, 18 Sep 2007 20:20:58 -0700, John Larkin a écrit:

On Wed, 19 Sep 2007 00:17:53 GMT, Joerg
wrote:

John Larkin wrote:

I was playing with our new spectrum analyzer and decided to just hang
a 12" cliplead off the input to see what was floating around.

See pics. The biggest signal was about -26 dBm, an FM station I guess.
Just about every slot on the FM band is full.


Looks like a luxury analyzer. Aeroflex? I thought you could buy those
only with a GSA account or for government contract work.


It's the new 3 GHz Aeroflex; anybody can buy it. With all the options
(tracking gen, preamp, high resolution) it was $13K or something. It has
a few firmware bugs, but I think they're sincere about fixing them.
Except for a few glitches, it's a lovely box, with a beautiful display.

I was disappointed in the harmonic distortion, -65 dB typically, but it
looks like that's actually not real bad compared to other units. We have
some RF signal generators that have THD numbers like 1.5%!

To test some amps we're doing, I guess we'll have to buy a few sets of
matched lowpass/highpass filters, so we can pump in a clean sinewave,
then and pull out the fundamental before we feed it to the spectrum
analyzer. What a nuisance. Maybe we should find/make a couple of tunable
notch filters.

How does one measure the THD of an amplifier, down around -70 dbC, in
the 1-30 MHz range maybe?

Why don't spectrum analyzers do log sweeps?


Some do, some don't.
I've both, one of which can nicely do linear and log sweeps.

-65dB isn't that bad, depending at which level it is specified.
To measure lower (but not extreme) THD without notching out the
fundamental, you can lower the input level (2nd order SA distorsion will
lower at twice the rate, 3rd at 3 times the rate, ...), and regain the
dynamic range by lowering the IF bandwidth.

You can easily check how low a level you have to go with a BP filtered
gen.

--
Thanks,
Fred.

John Larkin wrote:
On Wed, 19 Sep 2007 00:17:53 GMT, Joerg
wrote:


John Larkin wrote:


I was playing with our new spectrum analyzer and decided to just hang
a 12" cliplead off the input to see what was floating around.

See pics. The biggest signal was about -26 dBm, an FM station I guess.
Just about every slot on the FM band is full.


Looks like a luxury analyzer. Aeroflex? I thought you could buy those
only with a GSA account or for government contract work.



It's the new 3 GHz Aeroflex; anybody can buy it. With all the options
(tracking gen, preamp, high resolution) it was $13K or something. It
has a few firmware bugs, but I think they're sincere about fixing
them. Except for a few glitches, it's a lovely box, with a beautiful
display.


Hmm, when I bought a PC-controlled receiver for EMI debug purposes
lately they told me I can only have a version where the cell bands have
been disabled. That's because this thing could decode stuff which I
really need to identify sources or gauge their phase noise. Only gov
folks can buy the full range version. Importing a model for foreign
markets without such restrictions would not have been legal. They show
up on Ebays at times but I guess instead of the Fedex truck another
vehicle would ...


I was disappointed in the harmonic distortion, -65 dB typically, but
it looks like that's actually not real bad compared to other units. We
have some RF signal generators that have THD numbers like 1.5%!


For wideband outputs it's probably the usual trade-off between
dissipation in the final amp and linearity. Or maybe the engineers
didn't care.


To test some amps we're doing, I guess we'll have to buy a few sets of
matched lowpass/highpass filters, so we can pump in a clean sinewave,
then and pull out the fundamental before we feed it to the spectrum
analyzer. What a nuisance. Maybe we should find/make a couple of
tunable notch filters.

How does one measure the THD of an amplifier, down around -70 dbC, in
the 1-30 MHz range maybe?


We used to do that the old-fashioned way with bolometer heads. One
measurement at full BW, then the harmonics via a steep enough highpass
where whatever of the fundamental pipes through is subtracted. I always
keep a sizeable stash of toroids to whip up a filter.


Why don't spectrum analyzers do log sweeps?


I've used a few that did. And my network analyzer does. For spectrum
analyzers it is rarely needed though. I guess with a modern machine like
the Aeroflex you could pipe it through USB and then let Excel re-scale
it. Don't know about your analyzer but most modern gear unfortunately
does not come with SW that allows direct live import into Excel. I do
not understand why but Excel certainly does not provide an easy path
through a virtual COM port (wrestling with that right now). I have no
idea why Senor Gates has restricted the license for mscomm.ocx so you
can only use it when you also have VB6 installed on the PC banging head
on table.

--
Regards, Joerg

http://www.analogconsultants.com

On Wed, 19 Sep 2007 01:13:06 -0700, ChairmanOfTheBored
wrote:

On Tue, 18 Sep 2007 20:20:58 -0700, John Larkin
wrote:

How does one measure the THD of an amplifier, down around -70 dbC, in
the 1-30 MHz range maybe?

Why don't spectrum analyzers do log sweeps?


Use a loop analyzer.

What's that?

John

John Larkin wrote:

On Wed, 19 Sep 2007 01:13:06 -0700, ChairmanOfTheBored
wrote:


On Tue, 18 Sep 2007 20:20:58 -0700, John Larkin
wrote:


How does one measure the THD of an amplifier, down around -70 dbC, in
the 1-30 MHz range maybe?

Why don't spectrum analyzers do log sweeps?


Use a loop analyzer.


What's that?


Telco test boxes. They can gauge the quality of stuff such as DSL lines
but I am not sure you'll get much for the 30MHz range from them.

--
Regards, Joerg

http://www.analogconsultants.com

"John Larkin" wrote in message
...
Why don't spectrum analyzers do log sweeps?

I'd love to know what the answer is if you ever find it; I've often wished for
the same thing.

"Joerg" wrote in message
...
Hmm, when I bought a PC-controlled receiver for EMI debug purposes lately
they told me I can only have a version where the cell bands have been
disabled.

That's because what you're buying is being sold as a "radio." When you buy
"test and measurement" equipment, no such silliness applies.

Only gov folks can buy the full range version.

Yeah, but with many receivers it's just a matter of cutting a jumper or
removing a diode to enable it -- the hardware is often 100% the same.

It's a stupid law anyway.

Joel Kolstad wrote:

"Joerg" wrote in message
...

Hmm, when I bought a PC-controlled receiver for EMI debug purposes lately
they told me I can only have a version where the cell bands have been
disabled.


That's because what you're buying is being sold as a "radio." When you buy
"test and measurement" equipment, no such silliness applies.


Tried that one. Didn't work. Once it's categorized as a radio it remains
a radio, no matter how you turn it. They were very friendly and took
time to explain. Basically it's because of the capability to listen in
and to dump data into a computer. I wouldn't have needed the latter but
I do need the ability to listen to RF sources in client's systems which
is why a regular spectrum analyzer doesn't cut it for this kind of job
(they don't have single sideband demodulators).


Only gov folks can buy the full range version.


Yeah, but with many receivers it's just a matter of cutting a jumper or
removing a diode to enable it -- the hardware is often 100% the same.


Not on this one. It's mask programmed in the CPU and that is probably
some huge BGA you couldn't possibly get off.


It's a stupid law anyway.


Yes. Because all it takes to skirt it is buy it elsewhere and
hand-carry. Or build an up-converter. But, it ain't legal so I won't do
any of that. Should I ever have to listen to internal noises in that
area I could still connect it to an IF out of a regular analyser.

--
Regards, Joerg

http://www.analogconsultants.com

Joel Kolstad wrote:

"John Larkin" wrote in message
...

Why don't spectrum analyzers do log sweeps?


I'd love to know what the answer is if you ever find it; I've often wished for
the same thing.


I guess all this would be easy via Excel if Billy wouldn't have slapped
that strange license block on mscomm.ocx :-(

--
Regards, Joerg

http://www.analogconsultants.com

"Joerg" wrote in message t...
Joel Kolstad wrote:

"John Larkin" wrote in message
...

Why don't spectrum analyzers do log sweeps?


I'd love to know what the answer is if you ever find it; I've often wished for the same thing.


I guess all this would be easy via Excel if Billy wouldn't have slapped that strange license block on mscomm.ocx :-(

--
I've done some work with the windows API's for comms. Maybe I can come up with some VB code to use in Excel. I just need a
serial device to futz around with.

Cheers

Martin Riddle wrote:

"Joerg" wrote in message t...

Joel Kolstad wrote:


"John Larkin" wrote in message
...


Why don't spectrum analyzers do log sweeps?


I'd love to know what the answer is if you ever find it; I've often wished for the same thing.


I guess all this would be easy via Excel if Billy wouldn't have slapped that strange license block on mscomm.ocx :-(

--

I've done some work with the windows API's for comms. Maybe I can come up with some VB code to use in Excel. I just need a
serial device to futz around with.


You might want to take a look at David Hitchner's work:
http://www.thescarms.com/VBasic/commio.aspx

I'll have to get my hands around this stuff but for an analog guy that
is not easy. My exposure to Basic to date is close to zero.

--
Regards, Joerg

http://www.analogconsultants.com

Joerg wrote:
Joel Kolstad wrote:

"John Larkin" wrote in
message ...

Why don't spectrum analyzers do log sweeps?


I'd love to know what the answer is if you ever find it; I've often
wished for the same thing.


I guess all this would be easy via Excel if Billy wouldn't have slapped
that strange license block on mscomm.ocx :-(

So use the spreadsheet calculator that lives in OpenOffice.org. It works
better than Excel, and has nothing added by Billy.

-Chuck

Chuck Harris wrote:

Joerg wrote:

Joel Kolstad wrote:

"John Larkin" wrote in
message ...

Why don't spectrum analyzers do log sweeps?



I'd love to know what the answer is if you ever find it; I've often
wished for the same thing.


I guess all this would be easy via Excel if Billy wouldn't have
slapped that strange license block on mscomm.ocx :-(


So use the spreadsheet calculator that lives in OpenOffice.org. It works
better than Excel, and has nothing added by Billy.


But AFAICT that uses quite esoteric languages for comms and because of
the absence of VBA it is incompatible to Excel code that uses VBA. Also,
OO is too bloated for my taste and I don't like memory leaks.

--
Regards, Joerg

http://www.analogconsultants.com

ChairmanOfTheBored wrote:

On Wed, 19 Sep 2007 23:28:40 GMT, "Martin Riddle"
wrote:


"Joerg" wrote in message t...

Joel Kolstad wrote:


"John Larkin" wrote in message
m...


Why don't spectrum analyzers do log sweeps?


I'd love to know what the answer is if you ever find it; I've often wished for the same thing.


I guess all this would be easy via Excel if Billy wouldn't have slapped that strange license block on mscomm.ocx :-(

--

I've done some work with the windows API's for comms. Maybe I can come up with some VB code to use in Excel. I just need a
serial device to futz around with.

Cheers


Nat'l Instruments LabView... output to spreadsheet, and create process
to view the data in various ways.


But first plunk down a bag of gold for each seat. For start-ups that's
often not in the cards.

--
Regards, Joerg

http://www.analogconsultants.com