dynamic range questions

[Corboy - Poteet]

I've got some questions for the receiver meisters. These are not K3
questions but will affect my understanding of the K3 specs when they
appear.

IMD for the K3 (Orion, FTxxx, etc) refers to spurious signals produced
by operation of a stage (or stages) in the nonlinear portion of its
transfer curve (or whatever it's called)?

The measurement "ground rules" imply two signals: one at fc and the
other at fc+x, where "x" is 20khz, 10khz, ... ?

The parameter usually being determined is referred to as the two tone
dynamic range and indicates the point at which third order signals
resulting from 2fc-(fc+x) and 2(fc+x)-fc begin to appear in the signal
path?

fc and fc+x are chosen to put (at least one of) the third order
signals in the IF passband?

I assume that receiver circuit characteristics before the roofing
filters (or IF bandpass filter) essentially determine the dynamic
range. However, dynamic range figures "always" seem to degrade for
small separations of fc and fc+x. Is this because fc and/or fc+x are
falling within the IF passband and are producing spurious signals in
the stages following the roofing filters?

For the case of strong signals in the IF passband, are the dynamic
range tests run with the AGC disabled? In actual operation, wouldn't
the AGC reduce signal levels below the point where distortion products
were being generated (in the stages following the roofing filters)?

The two tone test is only a proxy for the "real world". In actual
operation, if any signal (or signals) in the RF passband or mixer
passband exceeds the receiver dynamic range, will ALL of the signals
in the passband begin contributing third order products?

Is the magnitude of the third order distortion products a function of
the "degree" of the nonlinearity? Can different receiver models with
the same dynamic range numbers (operating under the same conditions)
differ considerably in the "signal strength" of junk signals?

When test results are "phase noise limited", what is going on? Is the
phase noise acting simply as RF noise that masks the spurious signals
being observed? Or is it acting as a "third signal" that mixes with fc
and fc+x and causes the production of third order products at a lower
signal level than fc and fc+x would alone?


Mike  W5FTD

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[Curt Milton]

Mike

for two tone dynamic range testing, both signals are
located intentionally outside the detection passband
(narrowest filter) of the receiver, and the receiver
is tuned so that one of the third order intermods is
within the passband.  

you may find that this is a useful reference:

http://www.arrl.org/tis/info/pdf/109435.pdf

when the measurement is bounded by phase noise, it
means that instead of introducing a distortion product
or reducing the level of a weak signal, instead the
phase noise introduced by the receiver itself
(generally the local oscillators) has degraded
detection of the weak signal.  

otherwise, you seem to be on the right track with your
understanding.  

73, curt

--- [hidden email] wrote:

> I've got some questions for the receiver meisters.
> These are not K3
> questions but will affect my understanding of the K3
> specs when they
> appear.
>
> IMD for the K3 (Orion, FTxxx, etc) refers to
> spurious signals produced
> by operation of a stage (or stages) in the nonlinear
> portion of its
> transfer curve (or whatever it's called)?
>
> The measurement "ground rules" imply two signals:
> one at fc and the
> other at fc+x, where "x" is 20khz, 10khz, ... ?
>
> The parameter usually being determined is referred
> to as the two tone
> dynamic range and indicates the point at which third
> order signals
> resulting from 2fc-(fc+x) and 2(fc+x)-fc begin to
> appear in the signal
> path?
>
> fc and fc+x are chosen to put (at least one of) the
> third order
> signals in the IF passband?
>
> I assume that receiver circuit characteristics
> before the roofing
> filters (or IF bandpass filter) essentially
> determine the dynamic
> range. However, dynamic range figures "always" seem
> to degrade for
> small separations of fc and fc+x. Is this because fc
> and/or fc+x are
> falling within the IF passband and are producing
> spurious signals in
> the stages following the roofing filters?
>
> For the case of strong signals in the IF passband,
> are the dynamic
> range tests run with the AGC disabled? In actual
> operation, wouldn't
> the AGC reduce signal levels below the point where
> distortion products
> were being generated (in the stages following the
> roofing filters)?
>
> The two tone test is only a proxy for the "real
> world". In actual
> operation, if any signal (or signals) in the RF
> passband or mixer
> passband exceeds the receiver dynamic range, will
> ALL of the signals
> in the passband begin contributing third order
> products?
>
> Is the magnitude of the third order distortion
> products a function of
> the "degree" of the nonlinearity? Can different
> receiver models with
> the same dynamic range numbers (operating under the
> same conditions)
> differ considerably in the "signal strength" of junk
> signals?
>
> When test results are "phase noise limited", what is
> going on? Is the
> phase noise acting simply as RF noise that masks the
> spurious signals
> being observed? Or is it acting as a "third signal"
> that mixes with fc
> and fc+x and causes the production of third order
> products at a lower
> signal level than fc and fc+x would alone?
>
>
> Mike  W5FTD
>
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[Geoffrey Mackenzie-Kennedy-2]

Curt,

Would you not agree that a 3rd Order dynamic range test performed with both
test tones placed outside of the IF filter's passband ,with a product in the
passband, does not provide a complete measure of a receiver's odd order IMD
performance but only that of its front end? A receiver with a "weak" cascade
following the IF filter might appear to be be a good performer based on
tests done this way, but will probably fall apart when two or more strong
signals enter the IF filter's passband. During the development of high
performance receivers common practice in my experience was to employ
multiple signal tests, two tones in the IF passband and one or two placed on
the skirts. I am aware of suggestions that have been made during the past
years regarding these test procedures used to evaluate amateur receivers,
likewise to restore proper useage of the term MDS which is another story :-)

73,
Geoff
GM4ESD


Curt Milton <[hidden email]> wrote:

> Mike
>
> for two tone dynamic range testing, both signals are
> located intentionally outside the detection passband
> (narrowest filter) of the receiver, and the receiver
> is tuned so that one of the third order intermods is
> within the passband.
>
> you may find that this is a useful reference:
>
> http://www.arrl.org/tis/info/pdf/109435.pdf
>
> when the measurement is bounded by phase noise, it
> means that instead of introducing a distortion product
> or reducing the level of a weak signal, instead the
> phase noise introduced by the receiver itself
> (generally the local oscillators) has degraded
> detection of the weak signal.
>
> otherwise, you seem to be on the right track with your
> understanding.
>
> 73, curt

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[Bill VanAlstyne W5WVO]

Geoffrey Mackenzie-Kennedy wrote:

> A receiver with a "weak" cascade following the IF filter might appear
> to be be a good performer based on tests done this way, but will
> probably fall apart when two or more strong signals enter the IF
> filter's passband.

Well... yeah,sure. That's why the K3 offers a selection of appropriately
narrow roofing filters at the 1st IF frequency. If you're trying to copy CW
with the 6 kHz AM filter inline, of course you're going to have problems, just
as you certainly do with all the up-conversion radios (like the TS-2000 I own)
with broad-as-a-barn-door roofing filters in the 1st IF. Strong off-frequency
signals within that wide passband will cause later stages to fall apart, no
question. That's why the K3 (and a few other radios like the Orions) are
designed the way they are -- to do everything possible to mitigate against
that possibility.

Bill / W5WVO


 During the development of high performance

> receivers common practice in my experience was to employ multiple
> signal tests, two tones in the IF passband and one or two placed on
> the skirts. I am aware of suggestions that have been made during the
> past years regarding these test procedures used to evaluate amateur
> receivers, likewise to restore proper useage of the term MDS which is
> another story :-)
> 73,
> Geoff
> GM4ESD
>
>
> Curt Milton <[hidden email]> wrote:
>
>
>
>> Mike
>>
>> for two tone dynamic range testing, both signals are
>> located intentionally outside the detection passband
>> (narrowest filter) of the receiver, and the receiver
>> is tuned so that one of the third order intermods is
>> within the passband.
>>
>> you may find that this is a useful reference:
>>
>> http://www.arrl.org/tis/info/pdf/109435.pdf
>>
>> when the measurement is bounded by phase noise, it
>> means that instead of introducing a distortion product
>> or reducing the level of a weak signal, instead the
>> phase noise introduced by the receiver itself
>> (generally the local oscillators) has degraded
>> detection of the weak signal.
>>
>> otherwise, you seem to be on the right track with your
>> understanding.
>>
>> 73, curt
>
>
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[Geoffrey Mackenzie-Kennedy-2]

Yes I agree, but not all up-conversion radios suffer from this problem. It
is a great pity that the design of amateur up-conversion radios do not seem
to include very strong IF amplifiers IIP3 in the +45dbm region, which allows
for some relaxation in roofing filter requirements , cost I suspect. Far
fewer close in spurious responses to deal with.

Geoff
GM4ESD

Bill W5WVO <[hidden email]> wrote:

> Well... yeah,sure. That's why the K3 offers a selection of appropriately
> narrow roofing filters at the 1st IF frequency. If you're trying to copy
> CW with the 6 kHz AM filter inline, of course you're going to have
> problems, just as you certainly do with all the up-conversion radios (like
> the TS-2000 I own) with broad-as-a-barn-door roofing filters in the 1st
> IF. Strong off-frequency signals within that wide passband will cause
> later stages to fall apart, no question. That's why the K3 (and a few
> other radios like the Orions) are designed the way they are -- to do
> everything possible to mitigate against that possibility.
>
> Bill / W5WVO

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[Don Wilhelm-3]

Geoff,

While all the situations that you pose are valid measurements, I believe
that the 'figure of merit' that should be applied is with both signals
within the receiver passband.  That alone will indicate the ability to
copy a weak signal in the presence of a strong one - that is basic BDR
(IMHO).
Third order blocking IMD is quite another thing - there are many
variables to consider.  The best that we can hope for is that the
'standardized' tests will provide a good indicator of the performance on
the real world - a receiver with narrow 'roofing filters' should excel
in that test - although the test reports should specify the filter
widths.  The close spacing tests go a long way toward simulating the
'real world', but are really only a set of conditions that are defined
for lab tests - the real world operating conditions may present an
entirely different set of parameters.

Current tests do consider MDS to be the minimum signal that can be
demodulated with no other considerations.  Right or wrong, that is the
way it is for now - something must be defined for lab measurements to be
valid - we just trust that they are adequate to be useful in actual
operating conditions.

73,
Don W3FPR


Geoffrey Mackenzie-Kennedy wrote:

> Curt,
>
> Would you not agree that a 3rd Order dynamic range test performed with
> both test tones placed outside of the IF filter's passband ,with a
> product in the passband, does not provide a complete measure of a
> receiver's odd order IMD performance but only that of its front end? A
> receiver with a "weak" cascade following the IF filter might appear to
> be be a good performer based on tests done this way, but will probably
> fall apart when two or more strong signals enter the IF filter's
> passband. During the development of high performance receivers common
> practice in my experience was to employ multiple signal tests, two tones
> in the IF passband and one or two placed on the skirts. I am aware of
> suggestions that have been made during the past years regarding these
> test procedures used to evaluate amateur receivers, likewise to restore
> proper useage of the term MDS which is another story :-)
>

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[Bill VanAlstyne W5WVO]

Don Wilhelm wrote:

> Third order blocking IMD is quite another thing - there are many
> variables to consider.  The best that we can hope for is that the
> 'standardized' tests will provide a good indicator of the performance
> on the real world - a receiver with narrow 'roofing filters' should
> excel in that test - although the test reports should specify the
> filter widths.

Rob Sherwood always specifies rig settings/options -- don't know about ARRL.
Not so much, I don't think. This should be done universally, and in detail.
The devil is definitely in the details here.

That said, I believe real-world performance can be expected to pretty much
follow the bench metrics, based on my own limited experience (especially on
the negative end). To wit:

Some years ago, before I was dry behind the ears in terms of understanding
receiver design concepts and metrics, I acquired a Kenwood TS-2000, seduced by
its sexy looks, multi-band multi-mode capabilitities, and so forth.

Having used this rig on 6M under difficult contest conditions (extraordinarily
strong sporadic-E openings with many S9+40 signals) over several years, I can
tell you for sure that this rig absolutely falls on its derrière in the
presence of nearby strong signals. It is the next thing to useless as a
contest radio, especially on SSB. (I don't think much of it on CW, either.)
Subsequent to my acquiring it, Rob Sherwood came out with his 2 kHz dynamic
range metrics, and these showed the TS-2000 to be almost at the bottom of the
pack in terms of 3rd-order IMD dynamic range (57 dB). ARRL's numbers pointed
in the same direction, though they only measured to 5 kHz separation.

This experience made a believer out of me, as the test data exactly
illustrated my own on-air experiences with this whoreson dog of a radio.  ;-)

On the other end of things, the TenTec Orion and Orion II continue to be the
contesters' radios of choice, despite the plethora of problems both these
radios have had with design, manufacturing, and firmware. I doubt that
steely-eyed contesters are going to stick with a problematical radio unless
there is really something going there in terms of basic performance that they
can't get anywhere else. At the end of the day, it's dyanamic range, dynamic
range, and dynamic range.

So yes, I do believe in receiver bench metrics!

Bill / W5WVO


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[Geoffrey Mackenzie-Kennedy-2]

Don,

Your suggestion that both applied signals should be in the receiver's
passband in order to obtain a 'figure of merit' agrees with the argument for
a more useful 3rd Order dynamic range test on amateur receivers, a
discussion which has been taking place for several years as far as I know.
Of course the phase noise of each test signal source has to be suitably low
in level at a very small offset to avoid corruption of the test results, or
if you like 'Test equipment phase noise limited' results. Assuming that the
receiver's 3rd Order dynamic range is not limited by its own LO's phase
noise, this requirement placed on the test equipment could be one reason for
resisting any change to the current test parameters however unsatisfactory
they might be. Arguably one could move up from the noise floor to determine
the 3rd Order dynamic range.

With regard to the protection provided by roofing filters, one approach used
during the design of specialized high performance receivers whose end cost
was not, within reason, a controlling factor was to assume that the filter
would not provide protection, although filter generated IMD was taken into
account. This meant that the IMD performance of the entire receiver was
maintained at a high level, and any protection provided by the filter was
'icing on the cake'. From that point on in the design process one could make
adjustments aimed at reducing power consumption and cost provided that the
receiver's  IMD performance within the filter's passband was not
compromised.

MDS as you appreciate means 'Minimum Discernible Signal' not a signal at the
noise floor. IIRC the term was first intended to quantify the signal which
could be discerned by a human or device connected to a receiver's output,
which certainly in the human case introduces a variable. Some people can
hear a signal well below the noise floor thanks to the filter between the
ears, others with impaired hearing may not hear the signal until it rises
well above the noise floor. You might be interested to read SM5BSZ's
comments on the misuse of the term MDS in QEX March / April 2006 page 36,
others have commented before.

Thank you for your comment.

73,
Geoff
GM4ESD


Don Wilhelm <[hidden email]> wrote:

> Geoff,
>
> While all the situations that you pose are valid measurements, I believe
> that the 'figure of merit' that should be applied is with both signals
> within the receiver passband.  That alone will indicate the ability to
> copy a weak signal in the presence of a strong one - that is basic BDR
> (IMHO).
> Third order blocking IMD is quite another thing - there are many variables
> to consider.  The best that we can hope for is that the 'standardized'
> tests will provide a good indicator of the performance on the real world -
> a receiver with narrow 'roofing filters' should excel in that test -
> although the test reports should specify the filter widths.  The close
> spacing tests go a long way toward simulating the 'real world', but are
> really only a set of conditions that are defined for lab tests - the real
> world operating conditions may present an entirely different set of
> parameters.
>
> Current tests do consider MDS to be the minimum signal that can be
> demodulated with no other considerations.  Right or wrong, that is the way
> it is for now - something must be defined for lab measurements to be
> valid - we just trust that they are adequate to be useful in actual
> operating conditions.
>
> 73,
> Don W3FPR

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[Corboy - Poteet]

Geoff, thank you very much for the response. I am posting to the list
as others may find your comments helpful.

Mike  W5FTD


------------------------------------



Mike,

A couple of comments before I crash - it is past 3 am here!!

> IMD for the K3 (Orion, FTxxx, etc) refers to spurious signals produced
> by operation of a stage (or stages) in the nonlinear portion of its
> transfer curve (or whatever it's called)?

Yes, and the test result should specify which spurious products e.g.
3rd Order.

> The measurement "ground rules" imply two signals: one at fc and the
> other at fc+x, where "x" is 20khz, 10khz, ... ?

This is where the "numbers game" starts! A proper test has both
signals in the passband along with the products, but the great
majority of commercial amateur receivers would not do too well. So
with great reluctance on the part of ARRL the spacing "x" has been
gradually decreased with both signals outside of the passband so that
the product being measured is within the passband.

> The parameter usually being determined is referred to as the two tone
> dynamic range and indicates the point at which third order signals
> resulting from 2fc-(fc+x) and 2(fc+x)-fc begin to appear in the signal
> path?

This would be the 3rd Order dynamic range. The dynamic range is
sometimes measured from the noise floor but not always. This is
because some amplifiers / mixers do not "behave" properly because the
level of the 3rd Order products over some part of the allowed input
level range does not increase at the rate of 3db for every 1db
increase in the level of the input signals.

> fc and fc+x are chosen to put (at least one of) the third order
> signals in the IF passband?

Yes.

> I assume that receiver circuit characteristics before the roofing
> filters (or IF bandpass filter) essentially determine the dynamic
> range. However, dynamic range figures "always" seem to degrade for
> small separations of fc and fc+x. Is this because fc and/or fc+x are
> falling within the IF passband and are producing spurious signals in
> the stages following the roofing filters?

Yes, and this is something that many designers seem to forget.

> For the case of strong signals in the IF passband, are the dynamic
> range tests run with the AGC disabled? In actual operation, wouldn't
> the AGC reduce signal levels below the point where distortion products
> were being generated (in the stages following the roofing filters)?

I believe that most if not all 3rd Order dynamic range tests on
amateur receivers are run with the AGC disabled, but don't quote me!
In actual operation the IMD generated by some types of AGC controlled
amplifier can get worse as AGC is applied. It is up to the designer to
do his job properly!

> The two tone test is only a proxy for the "real world". In actual
> operation, if any signal (or signals) in the RF passband or mixer
> passband exceeds the receiver dynamic range, will ALL of the signals
> in the passband begin contributing third order products?

Yes, how much will depend on individual levels and of course the
receiver design.

> Is the magnitude of the third order distortion products a function of
> the "degree" of the nonlinearity? Can different receiver models with
> the same dynamic range numbers (operating under the same conditions)
> differ considerably in the "signal strength" of junk signals?

Yes is the short answer. This is one good reason why 3rd Order dynamic
range tests should be done with both signals in the passband which can
expose problems which might exist after the IF filter in model A but
not in model B. IMD generated by IF filters can be a problem which
might not be fully exposed if the test signals are widely spaced. Two
major issues are of concern here (1) the effect of the filter on the
dynamic range of the driving stage and (2) the generation of IMD
products within the filter which are passed on to the following IF
cascade.


> When test results are "phase noise limited", what is going on? Is the
> phase noise acting simply as RF noise that masks the spurious signals
> being observed? Or is it acting as a "third signal" that mixes with fc
> and fc+x and causes the production of third order products at a lower
> signal level than fc and fc+x would alone?

Phase noise from a noisy LO has the effect of lifting the noise floor
and is involved in reciprocal mixing. "Phase Noise Limited" means that
the useful performance of the receiver has been compromised by LO
noise, for example the 3rd Order dynamic range is reduced or limited
by phase noise because there is less "headroom" between the increased
noise floor and the point where the receiver runs out of steam.
Reciprocal mixing takes place when the LO phase noise mixes with an
unwanted signal to produce a "noise" IF signal which could mask weak
real signals - an unwanted LO if you like.

I hope that this helps a little.

73,
Geoff
GM4ESD


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[Geoffrey Mackenzie-Kennedy-2]

My pleasure Mike, my 3am "Autopilot" appeared to be working, maybe!

One final comment. The two in passband signal tests will tell you how a
receiver will perform in use for example in a pile up situation where the DX
station is not working split, whereas the wide spacing tests will only give
you a hint. But you need very good test equipment.  As Bill W5WVO said in
his post "at the end of the day it's dynamic range".  Once a large dynamic
range has been obtained, then in CW receivers zero beat QRM stripping
circuitry can be introduced - but that is another subject.

73,
Geoff
GM4ESD


Corboy-Poteet <[hidden email]> wrote:

> Geoff, thank you very much for the response. I am posting to the list
> as others may find your comments helpful.
>
> Mike  W5FTD
>
>
> ------------------------------------
>
>
>
> Mike,
>
> A couple of comments before I crash - it is past 3 am here!!
>
>> IMD for the K3 (Orion, FTxxx, etc) refers to spurious signals produced
>> by operation of a stage (or stages) in the nonlinear portion of its
>> transfer curve (or whatever it's called)?

<snip>


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[Kevin Purcell-2]

Inline

On Jun 1, 2007, at 10:56 AM, [hidden email] wrote:

> I assume that receiver circuit characteristics before the roofing
> filters (or IF bandpass filter) essentially determine the dynamic
> range. However, dynamic range figures "always" seem to degrade for
> small separations of fc and fc+x. Is this because fc and/or fc+x are
> falling within the IF passband and are producing spurious signals in
> the stages following the roofing filters?

You have to consider which stages set the dynamic range of the  
receiver. In a well designed receiver it should be the first mixer  
that sets the dynamic range (not the RF amp, if one is used, the  
filter itself, the post-mixer amp or any of the IF or AF stages.

Yes (it's fc) that does the "damage" if it gets by a wide roofing  
filter to the post-filter amp.

An in-band measurement will give you some info on the first mixer and  
the crystal filter (the later starts to become an issue for mixers  
with a very high intercept). See Sherwoods measurements going down to  
2kHz seperation (though for CW signals this should still be outside  
the first filter).

It's a good idea to do the measurement at multiple seperation and to  
ALWAYS quote the separation with the dynamic range.

> For the case of strong signals in the IF passband, are the dynamic
> range tests run with the AGC disabled? In actual operation, wouldn't
> the AGC reduce signal levels below the point where distortion products
> were being generated (in the stages following the roofing filters)?

You normally have no AGC elements before the first mixer. It's  
usually all after the crystal filter as the filter a delay in system  
that will cause problems in getting the AGC loop well controlled.

Usually the AGC if off to make the measurement though.

> The two tone test is only a proxy for the "real world". In actual
> operation, if any signal (or signals) in the RF passband or mixer
> passband exceeds the receiver dynamic range, will ALL of the signals
> in the passband begin contributing third order products?

Yes, but only the strongest signals really make an impact. The  
spurious signals are third order products so they vary as the cube of  
the input power. Or their slope when you plot a graph in dB is three  
times steeper than the input power. The spurious signals increase  
twice as fast (on a logarithmic plot) as the input power increases.  
The intercept point is the power when the spurious signal is the same  
power as a single test tone. You can't actually get to that point --  
gain compression takes over 10 or 15dB before you hit that point.

This is a more serious issue for CW with discrete, narrow (50Hz),  
tones. The spurious signals often sound like "bad" morse code when  
two CW signals intermod together -- they're the product (the AND in a  
logical sense) of one or more CW transmissions. In other cases they  
can sound like a good CW signal (say a strong CW signal  
intermodulatinging with a SW broadcast carrier) on the wrong frequency.

For SSB there is less of an issue (in general). The power is spread  
over a 3kHz so the components are typically -18dB down on the same  
power CW signal (3kHz/50Hz) so you are less likely to hear the  
problem in the same RF environment. When it does manifest it's more  
like the noise floor increasing in stregth than discrete signals  
though in the case of an SSB signal intermodulating with a strong  
carrier you would hear a distorted SSB-like signal.

You can do the calculation to determine what a passband looks  
(sounds) like when using "non-equal power" tones for the DR test (or  
as you know them, the ham bands). Wes Hayward does it in his  
"Introduction to RF Design" book.

> Is the magnitude of the third order distortion products a function of
> the "degree" of the nonlinearity?

Yes. This non-linearity is what controls the intercept points -- the  
measure usually quoted for amplifiers, mixers and other devices (the  
3rd order intercept point is the default but of course there is a  
second order intercept point that is important too :-)

> Can different receiver models with
> the same dynamic range numbers (operating under the same conditions)
> differ considerably in the "signal strength" of junk signals?

By "junk signals" you mean spurious signals from (2nd or) 3rd order  
IMD so the answer is no.  Assuming they measure the same at the

But of course there are other differences (phase noise which might  
mask these effects) and other sources of spurious signals.

I'd recommend reading Peter E. Chadwick, G3RZP, QEX article "HF  
Receiver dynamic Range: How Much Do We Need?" (QEX May/June 2002,  
p36-41).

> A good receiver needs a dynamic range of about 100dB according to a  
> study by Peter E. Chadwick, G3RZP HF Receiver dynamic Range: How  
> Much Do We Need? which appeared in the May/June 2002 issue of QEX.
>
> The number 100dB for phase noise limited dynamic range given by  
> G3RZP refers to "SSB bandwidth" which means that the noise floor of  
> a good receiver has to be below -132dBc/Hz (3dB S/N loss, 3kHz  
> bandwidth).

When you have high dynamic range receivers then you get more and more  
interesting in phase noise!

In Europe you can and do see -10dBm signals at the antenna port  
around the 40m band (they're SW broadcasters). You might see similar  
levels in an urban environment from local hams (or other sources) too.

<http://www.nitehawk.com/sm5bsz/linuxdsp/optrx.htm>
<http://www.nitehawk.com/sm5bsz/digdynam/practical.htm>
--
73 DE N7WIM / G8UDP
Kevin Purcell
[hidden email]



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