No. Reflections are linear phenomena, so they don't generate signals on
any new frequencies, or convert the frequencies of signals.

Diodes, on the other hand, are nonlinear devices which can do that. They
can create harmonics from existing signals, and they can mix signals
together to produce signals on frequencies that equal the sum and
difference of various multiples of the signals being mixed. Likewise, a
strong signal or signals can drive a poorly-designed receiver front end
into a nonlinear region for the same effect.

It's easy to test for the diodes. Find a suspected mixing product, and
see if it goes away when you disconnect the diodes. To check your
receiver front end, put an attenuator between the antenna and the
receiver. A 500 ohm potentiometer should be adequate for the test. As
you increase the attenuation, receiver mixing products will drop in
amplitude more quickly than valid signals. At some amount of
attenuation, you should hear only valid signals.

Roy Lewallen, W7EL

mike wrote:

After thinking about this a little more. What if my current impedance
mismatch between my antenna and transmission line is actually causing
reflections which are noticed by me as images on other frequencies?

Might a signal coming in on 3200 khz echo end to end back to 2300 khz?

This seems probable and the diodes may not be causing it at after all.

mike

I was going to make a comment but Roy covered it.


"Roy Lewallen" wrote in message
...
No. Reflections are linear phenomena, so they don't generate signals on
any new frequencies, or convert the frequencies of signals.

Diodes, on the other hand, are nonlinear devices which can do that. They
can create harmonics from existing signals, and they can mix signals
together to produce signals on frequencies that equal the sum and
difference of various multiples of the signals being mixed. Likewise, a
strong signal or signals can drive a poorly-designed receiver front end
into a nonlinear region for the same effect.

It's easy to test for the diodes. Find a suspected mixing product, and
see if it goes away when you disconnect the diodes. To check your
receiver front end, put an attenuator between the antenna and the
receiver. A 500 ohm potentiometer should be adequate for the test. As
you increase the attenuation, receiver mixing products will drop in
amplitude more quickly than valid signals. At some amount of
attenuation, you should hear only valid signals.

Roy Lewallen, W7EL

mike wrote:

After thinking about this a little more. What if my current impedance
mismatch between my antenna and transmission line is actually causing
reflections which are noticed by me as images on other frequencies?

Might a signal coming in on 3200 khz echo end to end back to 2300 khz?

This seems probable and the diodes may not be causing it at after all.

mike

Mike,

You definitely sound like me about 10 years ago. I started with a RS DX-390
radio and went from there. You didn't mention what kind of Sony portable
you had, but the first thing I realized (regardless of antenna) -- was to
get a better SW radio. You did say you're on a budget and that makes it
frustrating at times. But if you're careful, you can find a good deal on
ebay or other sites. I've seen Drake R-8 radios sell for around $250.
(They sold for $1200 in late '93.)

As for a 'good' SWL antenna... I picked up two of the RS shortwave antenna
kits (@ $10 ea) and bought a Palomar balun with RG-8 coax. I used to have a
Drake R-8 but traded it (stupidly) for something else. I've had a Yaesu
FRG-100 but now own an Icom R-75.

I can recieve pretty well, but I too am bothered by noise. I believe mine
to be more atmospheric rather than homemade QRM. I found that antenna
height is pretty important. My 100ft longwire antenna sits anywhere from
20-35ft above ground -- never going below 20ft.

You didn't mention what kind of programs you are listening to? If you're
listening to SW broadcasts on AM, then you'll hear much more 'noise' on AM
then you would on sideband. If you're trying to listen to military or
other HF sideband traffic, then you might be disappointed. I could barely
get ham stations on my DX-390! When I received my Drake R-8, I was amazed
at how much traffic was out there on HF -- that I couldn't hear before. The
quality of radio make a huge difference. ;o)


-Nick
n7zya

"mike" wrote in message
...
Ok, I guess I have a handle on things now.
I am a newbie SWL still in learning mode.

To properly match the impedance of coax I must use a matching
transformer (sometimes 'incorrectly' called a longwire balun).

Guess I will have to take a look at the ICE 180, MLB, UMB...etc.

So with the tranformer my PI network tuner should resonate better (?)

I plan to keep using it regardless given its recently added back to
back voltage limiting diodes between input and ground and a static
bleed off resistor for DC to ground.

This is what I have going now and it has reduced noise.

I am running a 12 guage wire from the ground banana plug of my antenna
tuner to a copper wire brade that connects my TV antenna to a ground
rod. This composes one end of my coax ground to eliminate common mode
currents.


The other end is where the coax meets my 13 meter random wire hung on
a wooden fence.

Lacking a proper ground rod, I soldered a short length of 12 guage
wire from the coax sheild to the bottom of a diced up coat hanger (16
inches in length) and stripped away the 12 guage wire sheild for the
length of the hanger segment (exposing the copper). This I plunged
into the resonably moist soil under a lylac tree.

Hodge podge for sure. But I'm on a budget till my new job starts next
week.

Thanks for all the help,

Mike