Pete KE9OA wrote:
. . .
In conclusion, make sure that the IMD isn't being generated in your test
setup, and make sure that you are not exceeding the recommended RF input
level to the SBL-1.

A quick test for spurs being generated by the spectrum analyzer is to
increase the spectrum analyzer input attenuation by 10 dB. Real spurs
will drop 10 dB. Most spurs generated by the analyzer will drop a
greater amount -- 20 dB if they're second order, 30 dB if they're third
order, and so forth. If any spurs do drop more than 10 dB, you have to
reduce the SA attenuator setting or the input signal level to the SA --
at least the level of the signal(s) generating the spurs.

Roy Lewallen, W7EL

On Fri, 30 Jun 2006 06:48:45 -0500, "Pete KE9OA"
wrote:

What kind of spectrum analyzer are you using? What are the front end

I'm not using one the author of the thread is.

attenuator settings on the spectrum analyzer? What is your reference level?

Ask him not me.

All of these things, especially the front end attenuator settings, can
affect your result. If the 1st mixer in the spectrum analyzer is driven into
nonlinearity, you can see all kinds of IMD products that are generated in
the analyzer itself.
Also, why are you doing this test with the RF port of the mixer terminated
in 50 Ohms? This type of termination is only used when doing either return
loss tests or noise balance tests.
If you are driving the SBL-1 mixer with +7 to +9dBm of LO level and you are
driving the RF port with a signal that is at least 20dB below the 1dB
compression point of the SBL-1, the main things you should see at the I.F.
port are a supressed LO signal, an upper sideband that is about 7dB lower in
level than the RF injection level, and a lower sideband that is also about
7dB lower in level than the RF injection level.
The 1dB compression point on the SBL-1 is about 0dBm, so I would set the
level to the RF port at -20dBm. If you go above this level, you will see
higher conversion loss, and possibly more IMD products at the I.F. port of
the mixer.
In conclusion, make sure that the IMD isn't being generated in your test
setup, and make sure that you are not exceeding the recommended RF input
level to the SBL-1.

Pete

You top posted to a reply that I'd posted to and your context is way
off as a result. Go bat to the root of the thread and read the
posting again.

Briefly, he's seeing spurs every 25 or 50 khz with a LO in the 45mhz
region and NO RF on the input (unterminated RF port).

Allison



wrote in message
news
On Wed, 28 Jun 2006 07:43:20 -0500, tim gorman
wrote:

john wilkinson wrote:



Hi,
If I feed my second mixer into a spectrum analyser, and inject a
44.545MHz
LO, with no power to the first IF stage, I see spurs at about 48-50KHz
intervals on the mixer output, from 0 to the 455KHz normal output freq.


The mixer is an SBL-1.

Any ideas as to where these are comming from?

Best regards,
John

A couple of observations.

If you simply disconnected the second mixer from the 1st mixer then it
sounds like you do not have the output of the 1st mixer properly
terminated. Unless, that is, the spectrum analyzer provides a good 50ohm
termination in the probe. The SBL-1 is a double-balanced mixer but in
order
to get the "balance" to work right you must properly terminate *all*
ports.
Otherwise all kinds of impedances can be "thrown" back to the other
ports -
causing all kinds of problems with attached LO's and RF stages.

Regularly spaced spurs from DC to 455khz does not sound like spurious
mixing
products. It sounds more like an oscillator being driven into saturation
causing square waves to be produced which are providing regular harmonic
outputs. This could be a product of poor terminations on the mixer ports.

Tim, the LO is 45.455 (or 44.545) either way there should be no LF
outputs from the mixer below the LO injection unless it's a spur on
the LO.

Directly connecting the output of a SBL-1 to the input of another mixer,
even another SBL-1, is not recommended either. The SBL-1 does not have
built-in terminations. A good, symmetric, 50ohm 3db pad between the stages
would provide a much better setup and would not significantly impact your
overall noise factor. Be sure and connect your spectrum analyzer to the
far
side of the pad.

Thats true though his testing is with a 20db IF after it and one would
hope that does present a 50ohm match to the IF port. Usually if the
poarts are badly matched the mixing spurs are greater and the port
to port isolation go to pot. If the only thing going in is the LO
then likely the LO is the source but if there is gain flollowing then
the gain stage is also suspect.

I've worked with enough SBL1 and MD108s and all their similar DBMS
to know the SBL1 in this case is not the offendor Even if
misterminated. Likely causes are the 45mhz filter is looking reactive
to the IF amp and the IF is unstable (makes a fine OSC) or there is
some other source of RF that is unaccounted for (spurs).


Allison
Kb!GMX

This thread is directed at the author, not you. The purpose of my posting in
the latest position of the thread is to move things in a chronological
order. The original poster knows how to read, so it is quite possible that
this person won't miss my posting.

Pete

wrote in message
...
On Fri, 30 Jun 2006 06:48:45 -0500, "Pete KE9OA"
wrote:

What kind of spectrum analyzer are you using? What are the front end

I'm not using one the author of the thread is.

attenuator settings on the spectrum analyzer? What is your reference
level?

Ask him not me.

All of these things, especially the front end attenuator settings, can
affect your result. If the 1st mixer in the spectrum analyzer is driven
into
nonlinearity, you can see all kinds of IMD products that are generated in
the analyzer itself.
Also, why are you doing this test with the RF port of the mixer terminated
in 50 Ohms? This type of termination is only used when doing either
return
loss tests or noise balance tests.
If you are driving the SBL-1 mixer with +7 to +9dBm of LO level and you
are
driving the RF port with a signal that is at least 20dB below the 1dB
compression point of the SBL-1, the main things you should see at the I.F.
port are a supressed LO signal, an upper sideband that is about 7dB lower
in
level than the RF injection level, and a lower sideband that is also about
7dB lower in level than the RF injection level.
The 1dB compression point on the SBL-1 is about 0dBm, so I would set the
level to the RF port at -20dBm. If you go above this level, you will see
higher conversion loss, and possibly more IMD products at the I.F. port of
the mixer.
In conclusion, make sure that the IMD isn't being generated in your test
setup, and make sure that you are not exceeding the recommended RF input
level to the SBL-1.

Pete

You top posted to a reply that I'd posted to and your context is way
off as a result. Go bat to the root of the thread and read the
posting again.

Briefly, he's seeing spurs every 25 or 50 khz with a LO in the 45mhz
region and NO RF on the input (unterminated RF port).

Allison



wrote in message
news
On Wed, 28 Jun 2006 07:43:20 -0500, tim gorman
wrote:

john wilkinson wrote:



Hi,
If I feed my second mixer into a spectrum analyser, and inject a
44.545MHz
LO, with no power to the first IF stage, I see spurs at about 48-50KHz
intervals on the mixer output, from 0 to the 455KHz normal output
freq.


The mixer is an SBL-1.

Any ideas as to where these are comming from?

Best regards,
John

A couple of observations.

If you simply disconnected the second mixer from the 1st mixer then it
sounds like you do not have the output of the 1st mixer properly
terminated. Unless, that is, the spectrum analyzer provides a good 50ohm
termination in the probe. The SBL-1 is a double-balanced mixer but in
order
to get the "balance" to work right you must properly terminate *all*
ports.
Otherwise all kinds of impedances can be "thrown" back to the other
ports -
causing all kinds of problems with attached LO's and RF stages.

Regularly spaced spurs from DC to 455khz does not sound like spurious
mixing
products. It sounds more like an oscillator being driven into saturation
causing square waves to be produced which are providing regular harmonic
outputs. This could be a product of poor terminations on the mixer
ports.

Tim, the LO is 45.455 (or 44.545) either way there should be no LF
outputs from the mixer below the LO injection unless it's a spur on
the LO.

Directly connecting the output of a SBL-1 to the input of another mixer,
even another SBL-1, is not recommended either. The SBL-1 does not have
built-in terminations. A good, symmetric, 50ohm 3db pad between the
stages
would provide a much better setup and would not significantly impact
your
overall noise factor. Be sure and connect your spectrum analyzer to the
far
side of the pad.

Thats true though his testing is with a 20db IF after it and one would
hope that does present a 50ohm match to the IF port. Usually if the
poarts are badly matched the mixing spurs are greater and the port
to port isolation go to pot. If the only thing going in is the LO
then likely the LO is the source but if there is gain flollowing then
the gain stage is also suspect.

I've worked with enough SBL1 and MD108s and all their similar DBMS
to know the SBL1 in this case is not the offendor Even if
misterminated. Likely causes are the 45mhz filter is looking reactive
to the IF amp and the IF is unstable (makes a fine OSC) or there is
some other source of RF that is unaccounted for (spurs).


Allison
Kb!GMX

I figured something like that occured. Sometimes, I even receive direct
e-mails from group postings. No offense intended.

Pete

wrote in message
...

Not to belabor but as explanation. I use Free Agent and it displays
in indented threaded form so your reply was nested two deep from
my first reply posting.

Allison
Kb1GMX

On Sat, 1 Jul 2006 14:50:17 -0500, "Pete KE9OA"
wrote:

This thread is directed at the author, not you. The purpose of my posting
in
the latest position of the thread is to move things in a chronological
order. The original poster knows how to read, so it is quite possible that
this person won't miss my posting.

Pete

wrote in message
. ..
On Fri, 30 Jun 2006 06:48:45 -0500, "Pete KE9OA"
wrote:

What kind of spectrum analyzer are you using? What are the front end

I'm not using one the author of the thread is.

attenuator settings on the spectrum analyzer? What is your reference
level?

Ask him not me.

All of these things, especially the front end attenuator settings, can
affect your result. If the 1st mixer in the spectrum analyzer is driven
into
nonlinearity, you can see all kinds of IMD products that are generated
in
the analyzer itself.
Also, why are you doing this test with the RF port of the mixer
terminated
in 50 Ohms? This type of termination is only used when doing either
return
loss tests or noise balance tests.
If you are driving the SBL-1 mixer with +7 to +9dBm of LO level and you
are
driving the RF port with a signal that is at least 20dB below the 1dB
compression point of the SBL-1, the main things you should see at the
I.F.
port are a supressed LO signal, an upper sideband that is about 7dB
lower
in
level than the RF injection level, and a lower sideband that is also
about
7dB lower in level than the RF injection level.
The 1dB compression point on the SBL-1 is about 0dBm, so I would set the
level to the RF port at -20dBm. If you go above this level, you will see
higher conversion loss, and possibly more IMD products at the I.F. port
of
the mixer.
In conclusion, make sure that the IMD isn't being generated in your test
setup, and make sure that you are not exceeding the recommended RF input
level to the SBL-1.

Pete

You top posted to a reply that I'd posted to and your context is way
off as a result. Go bat to the root of the thread and read the
posting again.

Briefly, he's seeing spurs every 25 or 50 khz with a LO in the 45mhz
region and NO RF on the input (unterminated RF port).

Allison



wrote in message
news On Wed, 28 Jun 2006 07:43:20 -0500, tim gorman
wrote:

john wilkinson wrote:



Hi,
If I feed my second mixer into a spectrum analyser, and inject a
44.545MHz
LO, with no power to the first IF stage, I see spurs at about
48-50KHz
intervals on the mixer output, from 0 to the 455KHz normal output
freq.


The mixer is an SBL-1.

Any ideas as to where these are comming from?

Best regards,
John

A couple of observations.

If you simply disconnected the second mixer from the 1st mixer then it
sounds like you do not have the output of the 1st mixer properly
terminated. Unless, that is, the spectrum analyzer provides a good
50ohm
termination in the probe. The SBL-1 is a double-balanced mixer but in
order
to get the "balance" to work right you must properly terminate *all*
ports.
Otherwise all kinds of impedances can be "thrown" back to the other
ports -
causing all kinds of problems with attached LO's and RF stages.

Regularly spaced spurs from DC to 455khz does not sound like spurious
mixing
products. It sounds more like an oscillator being driven into
saturation
causing square waves to be produced which are providing regular
harmonic
outputs. This could be a product of poor terminations on the mixer
ports.

Tim, the LO is 45.455 (or 44.545) either way there should be no LF
outputs from the mixer below the LO injection unless it's a spur on
the LO.

Directly connecting the output of a SBL-1 to the input of another
mixer,
even another SBL-1, is not recommended either. The SBL-1 does not have
built-in terminations. A good, symmetric, 50ohm 3db pad between the
stages
would provide a much better setup and would not significantly impact
your
overall noise factor. Be sure and connect your spectrum analyzer to
the
far
side of the pad.

Thats true though his testing is with a 20db IF after it and one would
hope that does present a 50ohm match to the IF port. Usually if the
poarts are badly matched the mixing spurs are greater and the port
to port isolation go to pot. If the only thing going in is the LO
then likely the LO is the source but if there is gain flollowing then
the gain stage is also suspect.

I've worked with enough SBL1 and MD108s and all their similar DBMS
to know the SBL1 in this case is not the offendor Even if
misterminated. Likely causes are the 45mhz filter is looking reactive
to the IF amp and the IF is unstable (makes a fine OSC) or there is
some other source of RF that is unaccounted for (spurs).


Allison
Kb!GMX