RadioBanter - View Single Post - Loop Antennas / minijack works-clips don't / impedence??

Telamon · August 23rd 06, 05:07 AM posted to rec.radio.shortwave

In article .com,
"RHF" wrote:

Telamon wrote:
In article . com,
wrote:

RHF wrote:
wrote:
Thanks.

I was asking if the tubing made a difference, so that I could
TEST using insulated wire directly on the antenna... and then get
some tubing once I see that the wrapping works and how many wraps
are needed.

1 - If you Wrap the Insulated Wire Directly on-to the Whip
Antenna : Then you have a Fixed {Permenant} Installation on the
one Radio.

DANR - Yes - The Tubing will make a difference.

Since the Insulated Wire will be closer to the Metal of the Whip
Antenna and therefore coupling to it more effectively. You will
find that few turns are required with the Direct-Wrap. More Turns
when the Tubing is used 'in-between' the Wire and the Whip Antenna.

TIP # 1 - Instead of Tubing for your first attempt. Try a few wraps
of Paper taped around the Whip Antenna as a Thin Core to make the
Coupling Coil more easier to Put-On or Take-Off as needed.

TIP # 2 - With the Tubing the Coil Assembly can be positioned
{move} In-and-Out on the Whip Antenna so that the Coupling Effect
between the Whip and Coil can be varried {adjusted} for the best
reception.

Well, I went from 10 wraps, to about 40 wraps (of the same 22 gauge
insulated wire), directly around the antenna. I extended the bottom
(thick) part of the antenna, just enough to fit the wraps (-the wraps
are NOT spaced out). I then attached antenna and ground wires of the
loop to the ends of the wire wrapped around the antenna.

Well, off of the rod by itself, I can hear CHU Canada, but it's below
1 on the S-Meter. Using the inductive connection (40 wraps), it gives
a signal of 4 -- but it's VERY noisy. (I tried reversing the
antenna/ground to no avail).

With the antenna clip directly to the top (thin part) of the rod
antenna (rest of rod not extended), I get signal of 6 but very noisy.
When I connect the ground clip to the battery, it get's MUCH quieter
(than without ground, or with inductive connection) and it stays at a
signal of 6. Direct connection of the antenna to a radio with an
antenna jack is still much better! (I did a test with the clips to
that radio - in order to make sure it's an antenna connection issue).

So, as of now, the inductive connection isn't helping. Suggestions or
recommendations?

I emailed Universal about the AA-1, to ask if it's ok to use with
active antennas (it's also $60...which is a bit much, considering).

- The radio input is a differential mode input. This means
- it see a signal relative to its internal ground.

- Most local noise is common mode so an antenna setup
- that picks it up and presents it to the radio input causes
- the radio to respond to it without a ground connection.

- Connecting an antenna to just the antenna terminal causes
- any received station by the antenna to look the same as any
- local noise it also picks up since both are presented to the
- radio as a signal to ground.

- Connecting an antenna to the radio antenna terminal and
- ground causes the received station to appear differentially
- across the radio input so the radio responds to it and the
- common mode locally picked up noise is the same on the
- antenna and ground terminal so it is rejected as a common
- mode signal.
-
- --
- Telamon
Ventura, California

El Telo Mundo - Translation Please ! ~ RHF

Is simply connecting an Antenna to the Radio's Whip
Antenna or Antenna Terminal :
- - - Good -or- Band for Reception ?

Is simply connecting a Ground to the Radio :
- - - Good -or- Band for Reception ?

Will doing both make Radio Listening Beter : Yes -or- No ?

You are confused by the terms differential and common mode?

Common mode means that you have the same voltage or signal on both
antenna and ground. Imagine a sine wave time varying voltage in phase
on the antenna and ground lead. Even though it is varying since it is
the same signal on both terminals it will not induce a current through
the radio input because there is no potential difference between the
terminals but if the signal was only on one terminal (antenna) then
there would be a potential difference and current will flow through the
radio input.

Consider a dipole antenna with one leg connected to the antenna and the
other leg connected to the ground terminal. A local noise field will
cause the same time varying voltage to be generated by both legs of the
dipole and then the radio terminals so that the radio does not respond
to it. However, a distant station will cause a time varying voltage 180
degrees out of phase to be generated and when that time varying
potential difference appears at the radio terminals that will cause a
current to flow from the antenna terminal to ground terminal.

The result of using a balanced antenna helps the radio reject local
noise while responding to the distant radio signal in this way. If we
were discussing amplifiers we would call it common mode rejection.

--
Telamon
Ventura, California