Hi Alan,
Due to visitors arriving tomorrow, I must make this my last post on the
subject we have been discussing.
I believe that this discussion started after Jack had warned that a square
wave source can get you into trouble if used to make 2nd and 3rd
intermodulation measurements, and noted
Hi Alan,
Indeed, most receivers do have some form of filter up front in the front
end, and therein lies one source of IMD measurement error if harmonics are
present in the applied test signals.
While the MiniCircuits application note AN-00-008 which Jack mentioned
points out that harmonics
Hi Geoff,
I guess I don't understand. Filters are linear devices. How can they
cause IMD? If the signal generator's harmonics are removed by the
receiver filters then it is the same as if the sig gen were clean, no?
73,
Alan N1AL
On Fri, 2011-04-15 at 11:54 +0100, Geoffrey
Only to a first approximation are filters linear.
Usually the major source of non-linearity is in the inductors. Even
powdered iron is non-linear to some degree. Ferrite is worse, of course.
Air is pretty close to perfect.
Capacitors are also non-linear at some level, as C is not constant with
Of course, if we didn't want to be able to copy with equal clarity
over a 100 dB input signal range, we could dispense with a lot of
this. AND do that with signals of the extremes separated by a mere 250
Hz. We are so picky. Why does anyone put up with us :)
You selling that T-shirt in bulk?
Sure, but if the filters are non-linear that's a whole different problem
that has nothing to do with harmonics in the signal source.
The question was whether signal generator harmonics are normally a
problem when measuring a receiver. I claim they are not because they
are removed by the filters
Is there any other communication system that requires the kind of close-in
dynamic range we do? It certainly wouldn't make much sense to design a
commercial system with such requirements. It seems likely we hams have the
toughest receiver dynamic range requirements on the planet.
Scott
Hi Alan,
Sorry that I was not here to reply to your previous e-mail.
With respect, filter non-linearity and the level of harmonics coming from
the signal sources are related in terms of the amplitude of the IMD products
seen at the output of the filter.
If the receiver being tested is perfect
Geoff, you're right. But I gather you're talking about two closely-spaced
sources?
I think the original question was whether harmonics from a *single* source
would
be a real problem. After all, this thread was originally about the XG3.
Generally, any harmonics aren't going to be a real big
Hi Geoff,
The case we're considering is where the test signal(s) are near the
receiver tuned frequency so they are well within the passband of the
input filters.
If the receiver's in-band dynamic range is significantly affected by
non-linear filters in the front end, then that is a serious
Getting a little far afield here and maybe a little pedantic (can you be just a
little pedantic?) mixer technology has progressed to the point that the mixer
no longer has to be the limiting factor.
Input filters and post mixer crystal filters are now the focus.
After having concentrated on
The more I have glanced through the specs for this device, the more
puzzled I have become. I grew up on signal generators that put out a
(good approximation to a) sine wave. This device is described as an RF
square wave generator, which I take to mean that the output wave shape
is a
Good questions. I had them myself, especially #2.
Wes
--- On Thu, 4/14/11, John Ragle tpcj1...@crocker.com wrote:
The more I
have glanced through the specs for this device, the more
puzzled I have become. I grew up on signal generators that
put out a
(good approximation to a) sine
...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of John Ragle
Sent: Thursday, April 14, 2011 1:15 AM
To: elecraft@mailman.qth.net
Subject: [Elecraft] XG3 device...
The more I have glanced through the specs for this device, the more
puzzled I have become. I grew up
On Thu, Apr 14, 2011 at 10:32 AM, Ron D'Eau Claire r...@cobi.biz wrote:
A square wave's frequency
Ron, I think John is aksing about the calibrated power (John, correct me
if I'm mis-stating here). If there are infinite harmonics each
with amplitude = 1/N, then 1/2 of the total energy will
All XG3 amplitude references refer to the amplitude of the fundamental
frequency component only.
Bob, N6CM
On Thu, Apr 14, 2011 at 9:09 AM, Tony Estep estept...@gmail.com wrote:
On Thu, Apr 14, 2011 at 10:32 AM, Ron D'Eau Claire r...@cobi.biz wrote:
A square wave's frequency
Ron,
Question 1: The frequency is based on the period of the square wave, in
other words, the frequency of the fundamental. If you program a
frequency greater than the maximum 200 MHz, software automatically
selects the proper fundamental so that the harmonic comes out at the
desired frequency.
It's implicit in Alan's posting, but note that symmetrical square waves have
only odd harmonics. The even harmonics will be very, very weak, present at all
only because the square wave isn't quite perfectly symmetric.
Scott K9MA
Scott Ellington
Madison, Wisconsin
USA
On Apr 14, 2011, at
Alan:
One are where a square wave RF source can get you into trouble is 2nd
and 3rd order intermodulation measurements.
Mini-Circuits Ap Note 8 discusses the reason why.
http://www.minicircuits.com/pages/pdfs/AN8.pdf
I usually use an outboard low pass filter on my HP 8657A signal
Hi Jack,
You're right that when testing a wide-band device like an amplifier you
have to filter out the generator harmonics in order to get a valid
third-order IMD test. But when testing a narrow-band device like a
receiver the harmonics are normally not an issue.
Those Coilcraft low-pass
Alan:
Coilcraft is direct sales only - no minimum quantity for internet orders
and they are pretty good about free samples if you have a business name
and address.
Jack K8ZOA
On 4/14/2011 5:58 PM, Alan Bloom wrote:
Hi Jack,
You're right that when testing a wide-band device like an
Hi Al,
You did say normally not an issue, but when making even or odd order
intermodulation measurements on a receiver the use of RF sources whose
harmonic content is significant can and usually will lead to invalid
results.
73,
Geoff
GM4ESD
On April 14, 2011 at 22:58 +0100, Alan Bloom
Hi Geoff,
Most receivers have bandpass and/or low-pass filters in the front end
that would filter out the harmonics of a square-wave test signal. I
could dream up some unusual situations where the harmonics could cause a
problem, but normally it would not be an issue.
Alan N1AL
On Fri,
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