RF interference issue again (esp. for E Drucker and Jim Weir and other RF wizards)

Ah, ok, thanks for that! What do they use? Is it standard?

Paul

"Jim Weir" wrote in message
...
You can stop playing with 10.7 as a source of the problem. I cannot
recall an
aircraft navcom using 10.7 as the IF frequency.

Nope. They are all over the map. I chose a random book from the library...it
happens to be the King KX-170B. The high COM IF is 9.0M and the low COM IF is
861.25k. The high NAV IF is 15.1875M and the low NAV IF is 1.1857M. I could
pick half a dozen books from the shelf and no two would be the same.

Jim


"Paul Sengupta"
shared these priceless pearls of wisdom:

-Ah, ok, thanks for that! What do they use? Is it standard?
-
-Paul
-
-"Jim Weir" wrote in message
.. .
- You can stop playing with 10.7 as a source of the problem. I cannot
-recall an
- aircraft navcom using 10.7 as the IF frequency.
-

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Blimey, thanks. Any idea how they decide to use these figures? Just out of
curiosity.

Paul

"Jim Weir" wrote in message
...
Nope. They are all over the map. I chose a random book from the
library...it
happens to be the King KX-170B. The high COM IF is 9.0M and the low COM
IF is
861.25k. The high NAV IF is 15.1875M and the low NAV IF is 1.1857M. I
could
pick half a dozen books from the shelf and no two would be the same.

Back in the old days we did it by trial and error and glommed onto what worked
best. When the digital computer came along, we got a full blown printout of the
inter/cross/spuri mod products across a frequency band and picked a
frequency(ies) for the IF that produced minimum spurious products.

Note the word MINIMUM. There has never been a receiver produced by the
superheterodyne process that is totally free of spurious, including the
magnificent Collins S-line or 51J series of receivers.

Jim



"Paul Sengupta"
shared these priceless pearls of wisdom:

-Blimey, thanks. Any idea how they decide to use these figures? Just out of
-curiosity.
-
-Paul
-
-"Jim Weir" wrote in message
.. .
- Nope. They are all over the map. I chose a random book from the
-library...it
- happens to be the King KX-170B. The high COM IF is 9.0M and the low COM
-IF is
- 861.25k. The high NAV IF is 15.1875M and the low NAV IF is 1.1857M. I
-could
- pick half a dozen books from the shelf and no two would be the same.
-

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

On Fri, 07 Nov 2003 12:39:37 -0800, Jim Weir wrote:

Back in the old days we did it by trial and error and glommed onto what worked
best. When the digital computer came along, we got a full blown printout of the
inter/cross/spuri mod products across a frequency band and picked a
frequency(ies) for the IF that produced minimum spurious products.

Note the word MINIMUM. There has never been a receiver produced by the
superheterodyne process that is totally free of spurious, including the
magnificent Collins S-line or 51J series of receivers.

And they were tube type equipment which I think did far better at
rejecting intermod than transistors. OTOH todays FETs are pretty good.

Of course a miser is a mixer is a mixer ... which was designed to mix
the signals. It takes sojme careful design to prevent unwanted signals
from getting into (and out of) the mixer.

As you say, none of them are perfect.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

Roger Halstead wrote:

On Fri, 07 Nov 2003 12:39:37 -0800, Jim Weir wrote:

Back in the old days we did it by trial and error and glommed onto what worked
best. When the digital computer came along, we got a full blown printout of the
inter/cross/spuri mod products across a frequency band and picked a
frequency(ies) for the IF that produced minimum spurious products.

Note the word MINIMUM. There has never been a receiver produced by the
superheterodyne process that is totally free of spurious, including the
magnificent Collins S-line or 51J series of receivers.

And they were tube type equipment which I think did far better at
rejecting intermod than transistors. OTOH todays FETs are pretty good.

Of course a miser is a mixer is a mixer ... which was designed to mix
the signals. It takes sojme careful design to prevent unwanted signals
from getting into (and out of) the mixer.

As you say, none of them are perfect.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)



I am sorry that I missed the beginning of the thread.

The King KX170 series is an excellent, if old, radio; and should be able to
regect the FM and VHF-TV band signals from as near as a couple of miles.

Nonetheless, your problem sounds like "front end overload" which is made
worse if the receiver has become slightly detuned over time. Therefore,
even though I usually assert that at least 80% of radio problems are really
antennas and other airframe wiring, I really thing that you will end up
sending the KX170 to the shop in order to solve this problem.

Peter