Do you believe that what I posted isn't true, or do you just wish it
isn't true?

Roy Lewallen, W7EL

CW wrote:
Classic. I new someone would come up with the "stick a coat hanger in your
antenna socket and be happy" line.

"Roy Lewallen" wrote in message
...

Try this simple test.

Tune your receiver to a part of the dial where there's no station.
Disconnect the antenna from your receiver. If the noise level drops,
impedance matching won't help your signal/noise ratio, it'll just make
everything louder. You can accomplish the same thing by turning up the
volume control.

Roy Lewallen, W7EL

On Fri, 4 Mar 2005 21:30:40 -0800, "CW" wrote:

Classic. I new someone would come up with the "stick a coat hanger in your
antenna socket and be happy" line.

As a rule I subscribe to the school that says every antenna should be
well-matched, in the clear and fed with low loss line, even those used
for receiving. Must come from my VHF/DXing background.

That said, I know my friend Roy is correct and I am wrong when he
gives this advice. Generally speaking, the SNR is set at the antenna
and nothing done after that will make much difference. This isn't
always the case if there are noise sources that can nulled or reduced
by phasing or other directive techniques that don't reduce the signal
simultaneously.

Roy did not mention this at all. He spoke to "impedance matching."

Wes N7WS

ps. You have no idea how hard it is to type with one (the "wrong")
hand while doing drugs. I had 2 1/2 hours of surgery putting my rt.
shoulder together on Thursday. Just in time to keep me out of the DX
contest---good planning



"Roy Lewallen" wrote in message
...
Try this simple test.

Tune your receiver to a part of the dial where there's no station.
Disconnect the antenna from your receiver. If the noise level drops,
impedance matching won't help your signal/noise ratio, it'll just make
everything louder. You can accomplish the same thing by turning up the
volume control.

Roy Lewallen, W7EL
[snip]

On Sat, 05 Mar 2005 06:18:45 -0700, Wes Stewart
wrote:

ps. You have no idea how hard it is to type with one (the "wrong")
hand while doing drugs. I had 2 1/2 hours of surgery putting my rt.
shoulder together on Thursday. Just in time to keep me out of the DX
contest---good planning


Hi Wes,

I don't think this will boost your spirits by more than one S-Unit,
but in today's NYT there was a report of a fellow that chopped off
both hands, and had them sewn back on.
graphic:
http://graphics8.nytimes.com/images/...n/05hands2.jpg
story:
http://www.nytimes.com/2005/03/05/nyregion/05hands.html

73's
Richard Clark, KB7QHC

On Sat, 05 Mar 2005 11:48:01 -0800, Richard Clark
wrote:

On Sat, 05 Mar 2005 06:18:45 -0700, Wes Stewart
wrote:

ps. You have no idea how hard it is to type with one (the "wrong")
hand while doing drugs. I had 2 1/2 hours of surgery putting my rt.
shoulder together on Thursday. Just in time to keep me out of the DX
contest---good planning


Hi Wes,

I don't think this will boost your spirits by more than one S-Unit,
but in today's NYT there was a report of a fellow that chopped off
both hands, and had them sewn back on.
graphic:
http://graphics8.nytimes.com/images/...n/05hands2.jpg
story:
http://www.nytimes.com/2005/03/05/nyregion/05hands.html

Oh my, that's gotta hurt.

Some years ago my wife had hand surgery and afterwards was getting
physical therapy. Another patient there had lost a thumb to a
circular saw. They made him a new one out of another finger.

On 02/03/2005 8:57 PM, Roy Lewallen wrote:
Try this simple test.

Tune your receiver to a part of the dial where there's no station.
Disconnect the antenna from your receiver. If the noise level drops,
impedance matching won't help your signal/noise ratio, it'll just make
everything louder. You can accomplish the same thing by turning up the
volume control.

Pulling the wire just attenuates the noise. So, a more balanced match
will not help with selectivity or overworked front-ends?

If this is the case, and a balun is most useful for transmitters trying
to manage SWR, then I guess it doesn't matter.

I'm still hoping that keeping all of the antenna outside may help with
household EMI. I sort of though that since I'm bothering to have a
transmission line, I may as well hack together a matching circuit for
efficiency.

On 10/03/2005 12:31 PM, clvrmnky wrote:
On 02/03/2005 8:57 PM, Roy Lewallen wrote:

Try this simple test.

Tune your receiver to a part of the dial where there's no station.
Disconnect the antenna from your receiver. If the noise level drops,
impedance matching won't help your signal/noise ratio, it'll just make
everything louder. You can accomplish the same thing by turning up the
volume control.

Pulling the wire just attenuates the noise. So, a more balanced match
will not help with selectivity or overworked front-ends?

If this is the case, and a balun is most useful for transmitters trying
to manage SWR, then I guess it doesn't matter.

.... in which case my only real choice is to shorten the antenna, or
attenuate the signal coming to my front-end a little ...

Hmmm. More to think about.

clvrmnky wrote:
On 10/03/2005 12:31 PM, clvrmnky wrote:

On 02/03/2005 8:57 PM, Roy Lewallen wrote:

Try this simple test.

Tune your receiver to a part of the dial where there's no station.
Disconnect the antenna from your receiver. If the noise level drops,
impedance matching won't help your signal/noise ratio, it'll just
make everything louder. You can accomplish the same thing by turning
up the volume control.

Pulling the wire just attenuates the noise. So, a more balanced match
will not help with selectivity or overworked front-ends?

If this is the case, and a balun is most useful for transmitters
trying to manage SWR, then I guess it doesn't matter.

... in which case my only real choice is to shorten the antenna, or
attenuate the signal coming to my front-end a little ...

Hmmm. More to think about.

You're on the right track, but more information might help.

Your antenna is picking up signal and noise. When you disconnect your
antenna, the antenna's signal and noise are removed, leaving only the
receiver's internal noise. The fact that the noise dropped means that
the noise being coming into the receiver from the antenna is larger than
the internal receiver noise. This is nearly always the case at HF and
nearly never the case at VHF and higher. As long as the noise from the
antenna dominates over the receiver noise, then improving the impedance
match, which is what the original question and answer were about, will
only make both the signal and noise (both coming from the antenna)
bigger. This is exactly what you get when you increase the volume, and
doesn't help the signal to noise ratio one bit. It therefore doesn't
help you hear signals.

There are other ways to help the signal to noise ratio, though. If a
signficant amount of the noise is originating locally, improving
feedline balance with a balun might help. Horizontal polarization will
often be less sensitive than vertical to moderately local noise sources,
because vertically polarized waves can propagate by surface waves while
horizontally polarized waves can't. Feedline balance also improves
rejection of vertically polarized waves when the antenna is horizontal.
This is because it prevents pickup from the feedline itself, which is
often partially, at least, vertical.

Increased antenna directivity will help if the signal and noise are
coming from different directions. But this requires a mechanically or
electrically rotatable antenna unless you're only interested in
listening in certain directions. Short wave listeners sometimes use a
small rotatable loop, which has sharp nulls which can be pointed toward
a single dominant noise source.

You mention an "overworked" front end. If your front end is getting
overloaded from strong signals, which usually manifests itself as
cross-modulation -- "ghost" signals created from existing signals at
different frequencies -- either a passive preselector or an attenuator
is needed. The former is better only if the loud signals are on
frequencies reasonably removed from the frequency where you're
listening. Adding attenuation is fine, until you add so much that the
receiver noise begins dominating. You can use the antenna-disconnection
test to check for that condition. Another way to attenuate the signal is
to *degrade* the impedance match. That's right, if overload is the
problem, you'll do better with a lousier match.

You also mention selectivity. A preselector can take care of attenuating
strong, out-of-band signals. But nothing you can practically do outside
the receiver will help you separate two signals which are close
together. That requires internal modification to the receiver.

Forget about SWR. It's not of any use in improving your ability to hear
signals at HF where the noise from the antenna dominates.

Roy Lewallen, W7EL

The answers you get on this group are likely to be far less than useful. I
would recommend rec.radio.shortwave.

"clvrmnky" wrote in message
...
I've got a little shortwave receiver that has a decent amount of gain in
it's antenna input. I've been experimenting with different lengths and
placements of the wire, and seen some interesting homebrew antennas I
might try once the snow melts.

I know that receivers are less demanding of impedance matching in
general, but my readings suggest that I should have a balun (unun) of
some sort to match the impedance better, since I'm pretty much stuck
with end-fed longwires. This should get more signal to my front-end,
and a proper shielded connection to my receiver should help minimize
stray RF noise.

I'm a renter, so I'm going to experiment with running a wire along the
eaves on the balcony, which is open to two sides of the house (wooden
two-story.) That is, I do not have the luxury of using the yard, trees
or anything.

So, my idea is to have a long wire (or folded longwire made from a
length of twin-lead) go to a balun (or unun, since this is really
unbalanced-to-unbalanced) and then run a downwire from there to my
receiver through a window.

I'm guessing the real advantage would be realized if I had a good RF
ground at the receiver and/or balun. This will be sort of tricky. I
don't even think I have copper cold-water pipes anywhere, and running
copper braid over the balcony, down the side of the building and into
6-foot rod just ain't going to happen. I've heard of people using
houseplants for poor grounds when no other was available, and I have
many kilos of wet earth on the balcony.

I've seen a neat artificial ground/antenna tuner from MFJ (I think)
which seems to offer a lot of bang for the buck. It even has multiple
inputs for high-Z single wires. Would this be useful for SW?

Finally, I'm probably just going to wind my own balun out of a ferrite
core. I just can't seem to find the details on how to wind the copper.
Do I wind the primary first around the whole core, and then the
secondary on top of it? Sorry if this is stupid question, but I've got
most of the math figured out (i.e., no. of turns and such) but since
I've never seen a balun... my assumption (right or wrong) is that it is
just a special transformer.

Thanks for your comments.

-- cm

CW wrote:
The answers you get on this group are likely to be far less than
useful. I
would recommend rec.radio.shortwave.

CW, I would suggest you refresh yourself on Signal-to-Noise Ratio, and
what it has to do with antennas. I took a look at the shortwave group,
and found a lot of garbage with little or no technical content. This
thread has had some excellent content, care to explain why it was far
less than useful?