Now I know it is getting late...................sorry about those typos!

Pete

"Pete KE9OA" wrote in message
...
The only way that this should happen is if either the receiver is very
conservatively rated (do we know exactly what method was use to make this
measurement?), or if the measurements were incorrectly done. I am not sure
that real world performance would reflect those measurements, unless you
are
in an area where there are several strong signals that are only 5kHz
apart.
When I am measuring the overload point on the receiver that I am
developing,
it is very easy to drive the system into overload with a signal generator,
yet with a 100 foot longwire in the presence of three 50kW MW
broadcasters,
no overload is present.
I think that specs do tell the story, if the measurement system is
properly
set up.
As an example, on one project, I needed to make some desense measurements
from 5kHz to several hundred MHz away from the desired signal. The desired
signal level was -140dBm. Using an HP8657 or an 8640B, the broadband noise
from these two units was so high, even a 300MHz away from the desired
signal, that I had to run the generators through a K&L tunable filter. The
only generator that was slightly usable was an HP8642B. This is the one
that
uses the Modulated Fractional Divider, with the Sigma-Delta modulation.
In reference to you statement about the receiver working better than its
rated specs, I just don't think so, unless as I said earlier, the
measurements were done incorrectly. The only way to really to a close-in
IP3
measurement is to run the interfering signal through a very selective,
deep
skirted crystal filter. You need the interfering signal to have almost
non-existant close-in phase noise; otherwise, the measurement is
meaningless.

Pete

"Telamon" wrote in message
...
In article , "phil "
wrote:

hi Eric:

i am responding here as my reader ate the thread...

You can mark the group unread or un-subscribe and re-subscribe to the
group to get all messages on the news server.

snip

But at very different signal strenghts and with very different
characteristics: The R8B overloaded abruptly -- switching in a 1 dB
step was enough to have it operating normally or overloaded. The
R75,
by contrast, had this "mushy" signal strength area.

neither radio is an IP3 god. a portable with LW loop will outperform a
radio hooked to a wire requiring 40+ dB attenuation.

Blindly reading specifications can lead you astray on how the radio will
perform. Some measurements require the radio be in a non-optimum
reception state.

I'm going to play devil's advocate and ask the question "why do some
radios work much better than the IP3 @ 5KHz measurement would indicate?"

Anybody feel free answer the question.

--
Telamon
Ventura, California