Spurs on mixer output

[Scott]

Have you looked at the 44.545 MHz injection signal with the spectrum
analyzer? What do you see there? Any spurs on it? I'm not exactly
sure how you have it set up...are you saying you have disconnected the
output of the 1st mixer so that it doesn't reached the 2nd mixer? If
so, what does the 44.545 signal mix with to get the 455 KHz 2nd IF?
Also, if the input to the 2nd mixer is simply disconnected, is the input
port of the 2nd mixer terminated somehow? Also, are you feeding the
proper level of 44.545 to it (not overdriving it are you??)? Not sure
what level is required for the SBL-1.

Scott
N0EDV

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

[Leon]

Scott wrote:
> Have you looked at the 44.545 MHz injection signal with the spectrum
> analyzer? What do you see there? Any spurs on it? I'm not exactly
> sure how you have it set up...are you saying you have disconnected the
> output of the 1st mixer so that it doesn't reached the 2nd mixer? If
> so, what does the 44.545 signal mix with to get the 455 KHz 2nd IF?
> Also, if the input to the 2nd mixer is simply disconnected, is the input
> port of the 2nd mixer terminated somehow? Also, are you feeding the
> proper level of 44.545 to it (not overdriving it are you??)? Not sure
> what level is required for the SBL-1.
>

+7 dBm.

Leon

[nospam@nouce.bellatlantic.net]

On Tue, 27 Jun 2006 21:37:44 +0100, 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

You have spurs on one or both of the inputs to the SBL1. Passive
doide mixers will not generate spurs like that though they may pass
them through if the sources are dirty.

Also the IF could also be oscillating and your see ing that
contribution. If its the 100db IF duscussed before, thats a lot of
gain and I'd hope its bypassed and shielded very well.

Allison

[john wilkinson]

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

[nospam@nouce.bellatlantic.net]

On Wed, 28 Jun 2006 19:48:20 +0100, john wilkinson
> wrote:

>> You have spurs on one or both of the inputs to the SBL1. Passive
>> doide mixers will not generate spurs like that though they may pass
>> them through if the sources are dirty.
>>
>> Also the IF could also be oscillating and your see ing that
>> contribution. If its the 100db IF duscussed before, thats a lot of
>> gain and I'd hope its bypassed and shielded very well.
>>
>> Allison
>Hi Allison,
>
>I have disconected the second mixer from the output of the first IF amp.
>That amp is powered down, and disconnected from any supply.
>The LO input to the mixer is from a crystal oscillator, at 7-8dBm.
>The output from the mixer is into the spectrum analyser only, not the
>second IF.
>
>This morning I did an experiment. If I left the RF port unterminated, the
>output was quite clean on the analyser.
>If I put a 50 Ohm term to gnd, the spurs appear.

Either the LO is dirty and your not seeing it due to overdriving the
analyser or the stages after SBL1 are dirty.

What I'd expect with the input of the SBL1 terminated and the LO
applied is the LO (40db or so down) some second and third harmonic
also way down and if you go far enough down some noise.

>Maybe it is on the LO itself, but looking at the LO on the analyser it
>looks OK to me.

Ok whats at the output of the SBL1? Or more specifically whats
between the SBL1 and the Analyser?


Allison

[tim gorman]

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.

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.

tim ab0wr

[john wilkinson]

On Tue, 27 Jun 2006 17:03:06 +0000, nospam wrote:

> On Tue, 27 Jun 2006 21:37:44 +0100, 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
>
> You have spurs on one or both of the inputs to the SBL1. Passive
> doide mixers will not generate spurs like that though they may pass
> them through if the sources are dirty.
>
> Also the IF could also be oscillating and your see ing that
> contribution. If its the 100db IF duscussed before, thats a lot of
> gain and I'd hope its bypassed and shielded very well.
>
> Allison
Hi Allison,

I have disconected the second mixer from the output of the first IF amp.
That amp is powered down, and disconnected from any supply.
The LO input to the mixer is from a crystal oscillator, at 7-8dBm.
The output from the mixer is into the spectrum analyser only, not the
second IF.

This morning I did an experiment. If I left the RF port unterminated, the
output was quite clean on the analyser.
If I put a 50 Ohm term to gnd, the spurs appear.

Maybe it is on the LO itself, but looking at the LO on the analyser it
looks OK to me.

Thanks,
John

[nospam@nouce.bellatlantic.net]

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

[Pete KE9OA]

What kind of spectrum analyzer are you using? What are the front end
attenuator settings on the spectrum analyzer? What is your reference level?
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

> wrote in message
...
> 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

[Steve N.]

This didn't sound like the problem if I read it correctly, but...
To test for analyzedr generated effects, switch-in 10 dB of attenuatin in
FRONT of the analyzer mixer (not in the analyzer IF). If the garbage drops
more than 10dB (like 20 or 30) then you are over driving the analyzer. If
it is coming from outside, then you'll se dB for dB changes.

73, Steve, K9DCI

Ain't the math of nonlinearity great?



"Pete KE9OA" > wrote in message
. ..
> What kind of spectrum analyzer are you using? What are the front end
> attenuator settings on the spectrum analyzer? What is your reference
level?
> 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
>
> > wrote in message
> ...
> > 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
>
>

[Roy Lewallen]

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

[nospam@nouce.bellatlantic.net]

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
...
>> 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
>

[Pete KE9OA]

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
...
>>> 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
>>
>

[Pete KE9OA]

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
...
>>>>> 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
>>>>
>>>
>>
>