Telamon wrote in
:

In article et,
Slow Code wrote:

"RHF" wrote in
ups.com:

For One and All,

QUESTION - Shortwave Listening (SWL) Antenna Tuners
- - - Do You Have An Opinion ? - - -

Why Antenna Tuners Aren't Necessarily Useful for Shortwave Listening
http://www.nyx.net/~dgrunber/tuner.ssi
- - - by - - - Daniel A. Grunberg

Here is "Dan Grunberg's Home Page"
http://www.nyx.net/~dgrunber/

Welcome - Here are some of my documents that may interest you.

TOPIC - SHORTWAVE RADIO :

* Advice to Shortwave Newbies
(Useful sources of information and useful links)

* Minimal Antennas and Grounds
(Why they may be all you need)

* So You're Certain You Need an Outdoor Antenna
(With a link to a reasonable design)

* Why Antenna Tuners Aren't Necessarily Useful
for Shortwave Listening
(This article could save you some money)

* A Rambling Review of the Lowe HF-150
(A nice receiver)

* Nifty 48-Inch (122-cm) Whip Antenna
with a PL-259 Connector

* The Sony 7600G and Its Synchronous Detector
(Why sync detectors are worth having)

* Analog vs. Digital Receivers (an introduction)

* Preventing Wire Antennas from Breaking in the Wind


and that's Today's On-Topic Post - iane ~ RHF
.
.
. .


Nice on-topic post. A tuner isn't really necessary for impedance
matching, but it can act as a pre-selector if your receiver has a poor
front end in it. Which can help improve things in some situations.

People like to argue about tuners and pre-selectors so I would like to
expand on this a little.

A pre-selector is basically a band pass filter. Main use is to attenuate
out of band signals that may, depending on how good your radios blocking
is, be very helpful in reducing false images from showing up and making
reception of in band signals messy and confusing. Some units are
adjustable to the point that even some in band signals can be
attenuated. This fine-tuning is good from the standpoint that radio has
a narrower range of signals to block and this should result in improved
signal to noise as any time you limit the bandwidth of a spectrum the
noise floor drops. Noise is broadband energy and any time you limit the
received bandwidth you reduce the noise power. Obviously the better the
receiver is designed the less there is to be gained by using a
pre-selector.

An antenna tuner is a circuit used to resonate an antenna at the
frequency of operation. The effect on reception appears similar but
occurs for a different reason. Because the action of the tuner causes
the antenna to be optimized for the frequency of operation, the range of
frequencies above and below it are relatively attenuated due to not
being picked up as efficiently so you get a similar result but for a
different reason.

Why is the distinction important? Because the pre-selector can go
anywhere in the transmission line (coax) from antenna to radio and is
most often conveniently located near the radio. The tuner needs to be a
part of the antenna and so is located there where its output is at the
coax transmission line to the radio.

The pre-selector is an in line band-pass filter that can go anywhere
along the transmission line. The antenna tuner is located at and is
actually a part of the antenna.

What's is that? You say hams use antenna tuners in the shack for
transmitting purposes. This is not a good practice but if they are using
an antenna that is close to resonance and are just trying to protect the
transmitter from dealing with the additional reflected power then its OK
but in using it they are not improving how well their antenna functions.
The tuner in the shack does not improve or change how well their antenna
radiates.

Another thing people keep endless repeating is that nether antenna
tuners or pre-selectors help and just make signals louder (they mean
stronger), which of course with the AGC operation of the radio means the
result of using either is the S meter reads higher. This is only true
for medium to strong signals. For a weak signal, the signal to noise
should at least have a small improvement, determined by how weak the
signal was to begin with, receiver design, local noise, and current
propagation. If the signal is very weak, the tuner and pre-selector
could result in it being readable. Here the antenna tuner has the best
possibility of making a signal that is below the receiver noise floor
strong enough to be heard (detected) on the radio.

In summery, in my opinion, a pre-selector would be a good bet to improve
portable reception when connected to an external antenna especially the
worse case single conversion units. Following that in usefulness would
be an antenna tuner. People chasing DX with tabletop units might want to
try antenna tuners where less useful for them would be pre-selector use.



As you said in your first sentence, people will argue about it. I agree
with what you say.

My point is that when you use a tuner with a receiver, it's acting as a
bandpass, which is the cause of the improvement if the receiver needs
front end help, Unwanted signals affecting the AGC are reduced. Impedance
matching with a tuner on HF I don't think you hear a difference. Maybe
we're meaning the same thing but saying it different ways.




SC