tuning a window frame
 

I suppose you could gamma match it.

--
Alec Wood M1BNK
Teesside UK

Interested in Ham Radio....have a look at www.ukradioamateur.org

"Ketalar" wrote in message
...
Subject to restrictions and poor location, I can't install any antenna.
My window has an aluminium frame.
I considered to use it as a loop, but it is inherently shorted.
How would you feed that ?
Freq : FM BC band.
Window : abt 0.90 * 1.60 (metres)
Thanks by advance.

Ketalar,
Assuming that the antenna would be for receiving only,
just connect a single wire between the receiver and the
window frame. Don't worry about 'matching'. And a second
wire from the radio's ground connection to ground. Will
there be an improvement in reception? Beats me! But it
shouldn't be difficult to find out...
'Doc

TNX fer the answer. That's what I was looking for, but I'm not an expert abt Gamma-matching : how should I proceed ?

Le Wed, 30 Jul 2003 13:07:39 +0100, Alexander S. Wood a écrit:

I suppose you could gamma match it.




--
A personne, sauf Ã* ceux qui y prendront plaisir (Franz Schubert, 1797-1828)

Subject to restrictions and poor location, I can't install any antenna.
My window has an aluminium frame.
I considered to use it as a loop, but it is inherently shorted.
How would you feed that ?
Freq : FM BC band.
Window : abt 0.90 * 1.60 (metres)
Thanks by adv

...........................................
Try connecting your leads (both) to various points on the window,you might get
lucky. I was able to achieve resonance with the windscreen
frame on a Sunbeam Tiger I restored. Luckily the spacing of the mounting studs
were close to the right tap points.
Works better the the usual 1/4 wave whip!
KC*VIF
Greg Z
to thine own sound be true

For instance, the distance between the two tap points : which one to start with , supposing I insert a variable capacitor (Sorry, the only antenna work I did was for top band) ??

Le Wed, 30 Jul 2003 18:38:09 +0200, ketalar a écrit:

TNX fer the answer. That's what I was looking for, but I'm not an expert abt Gamma-matching : how should I proceed ?

Le Wed, 30 Jul 2003 13:07:39 +0100, Alexander S. Wood a écrit:

I suppose you could gamma match it.







--
A personne, sauf Ã* ceux qui y prendront plaisir (Franz Schubert, 1797-1828)

But with the window open, or shut??
'Doc

I'll first try with the outer frame !
In summer I could turn (i.e. open) the window to see if there is an
improvement !

'Doc wrote in :



But with the window open, or shut??
'Doc

- Yes, that's only for receiving.
I need a decent signal for stereo, otherwise t is a bit noisy...
Coming back to the beginning of the discussion, I only wondered what
would be the approximate distance between the feedpoints (given the
size of the frame), and the capacitor range.
Gamma matching has always been a mystery for me....
Best regards to all,


On Fri, 01 Aug 2003 22:00:39 GMT, "Tim Conway"
wrote:

Incidentally, you do intend this as a receiver only, right?

thanks for the idea.
But I already tried this method : it does not work fine here : I'm between
concrete walls.

On Sat, 2 Aug 2003 05:28:21 -0400, WB3FUP (Mike Hall)
wrote:

For FM go to Radio Shack. Buy a folded dipole
(420-2385) for less than $5.00. Put it up as an
inverted V so that it is omni directional. Enjoy
your radio.




--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

On Sat, 02 Aug 2003 15:56:29 GMT, Richard Clark wrote:

Odd no one has actually answered your question.

- Maybe my poor english...

However, it pretty much depends on the physical dimensions of the
window frame (does the sash present a moving short across it?) before
a solid value would work. You also suffer a potential problem of it
pointing the wrong way to serve your needs (how would you tune it, if
it didn't hear anything?). Also, where you put the Gamma match would
also affect how it tuned up.

- No sash windows here in France ; they open (and close) like doors.
The window size is abt 0.90 * 1.60 (metres), which makes a gross 1.7 wave,
not so far from a 2 wavelenghts closed loop, like a square in a circle...
I suppose I could try to space my croc clips a quarter wave apart ??

Another point, if you just made the match a little longer, threw away
the capacitor, and screwed it to the wall instead; then it would
probably do just as well.
Hint: you may solve your problem more with height (put a simple
dipole up higher) than with tuning.

- You mean tap on top of the frame ?

73's
Richard Clark, KB7QHC

- Tnx es ame to you de F5LCI




--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

F5LCI wrote:
"The window size is abt 0.90 x 1.60 metres---."

The wavelength is near 3 metres at 100 MHz. So, the long dimension of
the window is slightly more than 1/2-WL. It can be considered (2)
short-circuited stubs back-to-back. At the low frequency end of the
band, the stubs may be near 1/4-wave and the antenna will be resonant.

Feed the window frame across its narrow (0.90 metres) dimension in the
centre of its 1.60m length.

The frame may be shorted acress its top and bottom to resonate the loop
(2 stubs) at higher frequencies for more response.

Kraus advises not to expect an efficient antenna made this way because
it has too little conducting materiel unless the frame is substantially
fattened. Plenty of folded dipoles and unipoles do very well without a
lot of conducting material. The difference must be in the feed
arrangement.

But, the application is for receiving, and you don`t usually need
efficiency, just good signal-to-noise ratio for success.

The window frame is there for a trial. With clips and feedline it can be
tried.

F5LCI can crank or swing his "loop" away from its closed position to see
if there`s any directional advantage. It is surrounded by conducting
materials which often cause directionality, intended or not.

Best regards, Richard Harrison, KB5WZI

- Tnx fer the answer.
As I said earlier I'm in a concrete building facing very close other ones : It is as if I am down a well...
Another problem is the hash generated by the nearby computer/screen : The s-meter does not tell all the truth. That's why I attached an external whip to the window : less noise, and why I want to use the window frame...
The xmitter, powerfull, is only two miles away but hidden by two hills : really, I am in a well !
More complicated, and hard to understand : I get a far better signal when rain is falling.

So far, I have never bought any antenna, only wire. (In another location, I had previously a nice setup on top-band as reported in RadCom abt 10 yrs ago).
I agree with you about amplified antennas.
Best regards,

Le Tue, 5 Aug 2003 17:23:31 -0400, WB3FUP (Mike Hall) a écrit:

And you put it up as an inverted v? Concrete walls does not absorb nearly
as much RF as one might think. If you are between concrete walls what do
you look at through your window. In more than 20 years I have found more
people that are convinced that they need to spend more money for an
antenna. I calculated the length necessary, and cut one myself to be used
in my cellar. I was amazed to see that what I had invested an hour in
constructing was identical to what I could have purchased for $4.00. (At
the time I had people lined up to pay me $50. to $100 an hour for my tax
preparation and planning expertise.) Building the antenna was not the
smartest use of my resources at the time. In fact my home rolled one did
not even look as good.

How far away are the stations you want to receive? If they are anything
like local, within 50 miles the antenna should work fine. Not the "T's"
you receive when you buy a receiver. The folded dipole the SKU of which is
below. I assumed you knew what I meant by Inverted V. The center of the
antenna is higher, or lower, than the ends. The ends include an angle of
between 90 and 150 degrees. (45 to 75 degrees off of the transmission line)
This makes the antenna omni-directional and it will work great.

But don't believe me. Continue to fight with the window frame, or go and
spend $40 to $60 on the amplified antennas that are sold, and that DO NOT
WORK.




--
A personne, sauf Ã* ceux qui y prendront plaisir (Franz Schubert, 1797-1828)

F5LCI wrote:
"Maybe the feedline needs sleeves?"

When the window is closed, its "balance" may be better, or it could be
worse.

Coax could be your bon ami in eliminating the computer display noise if
used with FM/TV baluns. Ground the shield to the radio. Ferrite sleeves
around the coax may reduce transport of the interference on the exterior
of the shield to the radio.

Best regards, Richard Harrison, KB5WZI

On Thu, 07 Aug 2003 19:25:14 +0200, ketalar wrote:


Tnx agn.
I already use coax (on coax input) whose shield is connected to mains
earth.
I'll try some ferrite. I'll have a look in my junk yard, there could be
ferrite sleeve baluns (as described by W2FMI). 73,

On Wed, 6 Aug 2003 07:31:48 -0500 (CDT), Richard Harrison
wrote:
Coax could be your bon ami in eliminating the computer display noise if
used with FM/TV baluns. Ground the shield to the radio. Ferrite sleeves
around the coax may reduce transport of the interference on the exterior
of the shield to the radio.

Hi OM,

I was listening to SW when I read your note above. As a test I put
the receiver against the display tube of my computer and didn't hear a
whisper of noise. The receiver's speaker magnet did affect the tube.
In fact, I run the audio through the computer's sound board to play
over my Hi-Fi speakers (three components to do one job). However, the
antenna is about 50 feet away with ferrites protecting it. I also use
the receiver on FM for stations about 10 miles away. No noise there
either.

You may need to put the ferrites on the computer leads (the source of
the noise rather than at the receiver of the noise).

73's
Richard Clark, KB7QHC

Tnx fer info.
Different setup here : the antenna is only 3 to 5 feet over the computer,
which could explain the hash...
I have the same problem at home, where the TR-7 is just behind the CRT.
Ferrite over all leads helps only a little. Last nite I fed the window
frame in the middle and, yes, the S-meter jumped 2 points up !
To avoid hash I had to put the coax away from the screen.
Best regards to all,

On Thu, 07 Aug 2003 17:36:58 GMT, Richard Clark wrote:
...the antenna is about 50 feet away with ferrites protecting it. I also
use
the receiver on FM for stations about 10 miles away. No noise there
either.