300 ohm twinlead antenna.
 

"tom" wrote in message ...

On 6/6/2013 4:18 PM, Channel Jumper wrote:
Geoffrey S. Mendelson;805681 Wrote:
Take a length of 300 ohm twinlead. Short the far end, End feed one side
of
the close end, and leave the other side disconnected.

What do I have?

I know if I short both ends, I have a wide(er) bandwidth end fed random
wire.

Is it still an end fed random wire with an electrical length of twice
its
physical length?

Something completely different?

If for example, if I have 10 meters of space, and hang it, will I have
a 20 meter long random wire, which would sort of be a 40 meter band
1/2 wave end fed antenna? Or would I have an odd 10 meter long end
fed antenna (for 20m?)

Can it be switched between the two by adding a shorting switch at the
close
end? Open it would be for 40m, and closed for 20?

TIA,

Geoff.


--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
It's Spring here in Jerusalem!!!

Get yourself a ARRL antenna book


# I have several different revisions of it but have never run across what
# Geoffrey is asking about. Could you please point to an example in the
# ARRL Antenna Book? And please give the revision.

# Thanks.

# tom
# K0TAR

If it were a single wire, there would be a voltage node at the end. If it
is instead a length of twin lead with one wire fed and the far end of the
twin lead shorted, I can't envision what would change. One possibility is
no change, another is that the voltage node would be back at the starting
point, and of course, something else.

My initial thoughts were that the voltage node would be at the far end of
the twin lead, with the return wire having close coupling to the fed wire.

After a little head scratching, and having some spare time, I plugged an
experiment into EZNEC.

I characterized a 16.5 foot whip over real ground and got a resonance at
14.4 MHZ at 36 ohms.

With the 300 ohm line simulated with the second wire separated by 0.05 foot,
there were resonances at 10.7 MHZ (4.7 ohms) and 19.6 MHZ (63 ohms).

My conclusion: I didn't model it correctly :)

Wayne W5GIE

300 ohm twinlead antenna.
 

"Wayne" wrote in message ...



"tom" wrote in message ...

On 6/6/2013 4:18 PM, Channel Jumper wrote:
Geoffrey S. Mendelson;805681 Wrote:
Take a length of 300 ohm twinlead. Short the far end, End feed one side
of
snip

OOOOOPS.....I've got a big error in the model.
Nevermind...I'll get back.

300 ohm twinlead antenna.
 

"Wayne" wrote in message ...



"Wayne" wrote in message ...



"tom" wrote in message ...

On 6/6/2013 4:18 PM, Channel Jumper wrote:
Geoffrey S. Mendelson;805681 Wrote:
Take a length of 300 ohm twinlead. Short the far end, End feed one side
of
snip

# OOOOOPS.....I've got a big error in the model.
# Nevermind...I'll get back.

OK, after correcting the error in my EZNEC model parameters, the results
were too weird to have significance.

300 ohm twinlead antenna.
 

On Monday, July 8, 2013 11:41:47 AM UTC-5, Wayne wrote:
OK, after correcting the error in my EZNEC model parameters, the results
were too weird to have significance.

Here's a zipped EZNEC file model of an 80m folded dipole.

http://www.w5dxp.com/80mFD.zip

300 ohm twinlead antenna.
 

W5DXP wrote:
On Monday, July 8, 2013 11:41:47 AM UTC-5, Wayne wrote:
OK, after correcting the error in my EZNEC model parameters, the results
were too weird to have significance.

Here's a zipped EZNEC file model of an 80m folded dipole.

http://www.w5dxp.com/80mFD.zip

Thanks, but my whole point was that it was not a folded dipole. It was an
end fed random (or 1/4 wavelength) wire connected to another 1/4 wavelength
wire at the far end, making it a 1/2 wavelength wire.

BUT since it is twinlead the 1/4 wavelength wires would be very tightly
capacitively coupled, which may between the capacitance and the poximity
make it not a 1/2 wavelength wire.

It was a thought to get another band out of a stretch of twinlead. Short the
far end. At the frequency it was 1/2 wavelength, use it as an end fed
wire with the near end shorted, and at half of that, use it as a 1/2
wavelength wire with the near end opened.

It does not seem that it will work that way.

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379
It's Spring here in Jerusalem!!!

300 ohm twinlead antenna.
 

"W5DXP" wrote in message
...

On Monday, July 8, 2013 11:41:47 AM UTC-5, Wayne wrote:
OK, after correcting the error in my EZNEC model parameters, the results
were too weird to have significance.

# Here's a zipped EZNEC file model of an 80m folded dipole.

# http://www.w5dxp.com/80mFD.zip

Thanks. I'm filing that away for future reference.