Hi,

There is no simple answer to your problem as the impedances
and frequency range involved are too great. However, as you are
not intending to use the antenna to transmit with, take a look at
this site and do a search on "LONG WIRE BALUN".

http://www.maplin.co.uk/

If you are in the U.S. I am sure that there will be an
equivalent item around somewhere. It is even possible that there
is a design for one of these out on the net.

The device is mis-named really and should be called something
like an UNUN. Of course it is a kludge but what the hell as it
should be better than a single wire or coax feed from your
basement.


Cheers - Joe, G3LLV

After doing a lot of reading on the web about long wires, short wires,
inverted L's, impedance matching, baluns, ununs, onions, fundip, and who
knows what else...

I was thinking (run for cover please)

Couldn't one simply use a small active device to buffer the straight wire
antenna at the end where it tethers to Ye Olde Oak tree or whatever it's
tied to? I was thinking you could even make it powered with a small gel
cell or something and a solar cell to power it. Some sort of wide-band
amplifier that would have a suitably high input impedance to accomodate the
higher and varying impedance of the wire over the desired frequency range,
and yet having a fixed 75 or 50 ohm output impedance to drive the coax that
runs back to the house. Then you could use a transformer in the house at
the receiver if it's the type that wants to be fed from a high-impedance. I
would think this would get around the problem of an impedance matching
transformer mismatching the antenna on frequncies where the antenna
impedance drops significantly. Also it could provide perhaps some minimal
gain to boot. Some of those commercial impedance matching transformers sell
for over $50 US. So I would think a small buffer amp might not be too
cost-ineffective.

Dave

After doing a lot of reading on the web about long wires, short wires,
inverted L's, impedance matching, baluns, ununs, onions, fundip, and who
knows what else...

I was thinking (run for cover please)

Couldn't one simply use a small active device to buffer the straight wire
antenna at the end where it tethers to Ye Olde Oak tree or whatever it's
tied to? I was thinking you could even make it powered with a small gel
cell or something and a solar cell to power it. Some sort of wide-band
amplifier that would have a suitably high input impedance to accomodate the
higher and varying impedance of the wire over the desired frequency range,
and yet having a fixed 75 or 50 ohm output impedance to drive the coax that
runs back to the house. Then you could use a transformer in the house at
the receiver if it's the type that wants to be fed from a high-impedance. I
would think this would get around the problem of an impedance matching
transformer mismatching the antenna on frequncies where the antenna
impedance drops significantly. Also it could provide perhaps some minimal
gain to boot. Some of those commercial impedance matching transformers sell
for over $50 US. So I would think a small buffer amp might not be too
cost-ineffective.

Dave

David Forsyth wrote:

After doing a lot of reading on the web about long wires, short wires,
inverted L's, impedance matching, baluns, ununs, onions, fundip, and who
knows what else...

I was thinking (run for cover please)

Couldn't one simply use a small active device to buffer the straight wire
antenna at the end where it tethers to Ye Olde Oak tree or whatever it's
tied to? I was thinking you could even make it powered with a small gel
cell or something and a solar cell to power it. Some sort of wide-band
amplifier that would have a suitably high input impedance to accomodate the
higher and varying impedance of the wire over the desired frequency range,
and yet having a fixed 75 or 50 ohm output impedance to drive the coax that
runs back to the house. Then you could use a transformer in the house at
the receiver if it's the type that wants to be fed from a high-impedance. I
would think this would get around the problem of an impedance matching
transformer mismatching the antenna on frequncies where the antenna
impedance drops significantly. Also it could provide perhaps some minimal
gain to boot. Some of those commercial impedance matching transformers sell
for over $50 US. So I would think a small buffer amp might not be too
cost-ineffective.

Dave

If you want to put a preamp near the antenna, you can run a DC
voltage up the coax by using RF chokes in the DC lines at both ends to
isolate the RF, and series coupling capacitors to block the DC. That is
how LNA/B/Cs are powered on most Sat TV receivers, and I have used it at
60 KHz, as well. You could use a Minicircuits chip that cost about
$1.00 by adding a couple caps, a coil and a resistor. Their ERA or MAR
series would do a good job, and the part is cheap enough that you can
afford to replace it when lightning takes out your preamp. I have some
rejected blank surface mount PC boards that will work for the part (They
were laid out wrong, and engineering had to eat the cost). You can also
do dead bug, or even use the old Vector Perfboard pins or standoffs and
build it point to point. They do need a ground plane, but are quite
stable.

These parts have a 50 ohm output, so they will match either 50 or 75
ohm coax with little problems. You might need a low pass filter to
remove out of band noise and signals to prevent overload, or if you want
to have real fun built a remote tuner at the preamp.
--


Michael A. Terrell
Central Florida

David Forsyth wrote:

After doing a lot of reading on the web about long wires, short wires,
inverted L's, impedance matching, baluns, ununs, onions, fundip, and who
knows what else...

I was thinking (run for cover please)

Couldn't one simply use a small active device to buffer the straight wire
antenna at the end where it tethers to Ye Olde Oak tree or whatever it's
tied to? I was thinking you could even make it powered with a small gel
cell or something and a solar cell to power it. Some sort of wide-band
amplifier that would have a suitably high input impedance to accomodate the
higher and varying impedance of the wire over the desired frequency range,
and yet having a fixed 75 or 50 ohm output impedance to drive the coax that
runs back to the house. Then you could use a transformer in the house at
the receiver if it's the type that wants to be fed from a high-impedance. I
would think this would get around the problem of an impedance matching
transformer mismatching the antenna on frequncies where the antenna
impedance drops significantly. Also it could provide perhaps some minimal
gain to boot. Some of those commercial impedance matching transformers sell
for over $50 US. So I would think a small buffer amp might not be too
cost-ineffective.

Dave

If you want to put a preamp near the antenna, you can run a DC
voltage up the coax by using RF chokes in the DC lines at both ends to
isolate the RF, and series coupling capacitors to block the DC. That is
how LNA/B/Cs are powered on most Sat TV receivers, and I have used it at
60 KHz, as well. You could use a Minicircuits chip that cost about
$1.00 by adding a couple caps, a coil and a resistor. Their ERA or MAR
series would do a good job, and the part is cheap enough that you can
afford to replace it when lightning takes out your preamp. I have some
rejected blank surface mount PC boards that will work for the part (They
were laid out wrong, and engineering had to eat the cost). You can also
do dead bug, or even use the old Vector Perfboard pins or standoffs and
build it point to point. They do need a ground plane, but are quite
stable.

These parts have a 50 ohm output, so they will match either 50 or 75
ohm coax with little problems. You might need a low pass filter to
remove out of band noise and signals to prevent overload, or if you want
to have real fun built a remote tuner at the preamp.
--


Michael A. Terrell
Central Florida

Even the car radio type coax would probably have too much capacitance
for the length of run you'll need. Yes, you could put a preamp
(actually an active impedance converter) near the antenna in order to
drive standard 50-ohm coax cable. I classify it as an "impedance
converter" because you probably don't need or want much gain, just the
ability to match the coax impedance. On the broadcast band any gain
will likely increase the noise level as much as the signals.

If you don't have too much noise pick up from the house electrical
wiring, etc you can probably just run a single wire feed line down
into the basement. Keep it as far away as possible from any conductive
material like rain gutters, etc.

Even the car radio type coax would probably have too much capacitance
for the length of run you'll need. Yes, you could put a preamp
(actually an active impedance converter) near the antenna in order to
drive standard 50-ohm coax cable. I classify it as an "impedance
converter" because you probably don't need or want much gain, just the
ability to match the coax impedance. On the broadcast band any gain
will likely increase the noise level as much as the signals.

If you don't have too much noise pick up from the house electrical
wiring, etc you can probably just run a single wire feed line down
into the basement. Keep it as far away as possible from any conductive
material like rain gutters, etc.

In looking at some of the options I was pointed to on this matter, it seems
perhaps the first thing I should do is run a simple wire down into the
basement as best I can and see how that fares. At least now Im armed with
some alternative ideas should that method prove too lossy/noisy.

thanks again to all who responded!

Dave



"Bob Lewis (AA4PB)" wrote in message
...
Even the car radio type coax would probably have too much capacitance
for the length of run you'll need. Yes, you could put a preamp
(actually an active impedance converter) near the antenna in order to
drive standard 50-ohm coax cable. I classify it as an "impedance
converter" because you probably don't need or want much gain, just the
ability to match the coax impedance. On the broadcast band any gain
will likely increase the noise level as much as the signals.

If you don't have too much noise pick up from the house electrical
wiring, etc you can probably just run a single wire feed line down
into the basement. Keep it as far away as possible from any conductive
material like rain gutters, etc.

In looking at some of the options I was pointed to on this matter, it seems
perhaps the first thing I should do is run a simple wire down into the
basement as best I can and see how that fares. At least now Im armed with
some alternative ideas should that method prove too lossy/noisy.

thanks again to all who responded!

Dave



"Bob Lewis (AA4PB)" wrote in message
...
Even the car radio type coax would probably have too much capacitance
for the length of run you'll need. Yes, you could put a preamp
(actually an active impedance converter) near the antenna in order to
drive standard 50-ohm coax cable. I classify it as an "impedance
converter" because you probably don't need or want much gain, just the
ability to match the coax impedance. On the broadcast band any gain
will likely increase the noise level as much as the signals.

If you don't have too much noise pick up from the house electrical
wiring, etc you can probably just run a single wire feed line down
into the basement. Keep it as far away as possible from any conductive
material like rain gutters, etc.

"David Forsyth" wrote in message ...
In the interest of my recent tinkerings with radios (both antique and
homebrew), I have put up an 80 foot straight wire antenna above the house.
It sits about 35 feet up from, and horizontal to, the ground. I am using a
lead in from one end made of insulated stranded copper wire (basically old
speaker cable, about 18 guage I think). Right now, the lead-in wire comes
down from the end of the antenna closest to the sun porch, and in through
the storm window via a well-insulated bushing. Due to the location of this
lead-in, this is the spot wherre I have been doing most of the tinkering
with the radios. I also have a copper pipe ground rod in a nearby location
so as to have as short a path to ground as possible.) It seems to work OK
for now but I would ideally like to run the lead-in into my basement where
my workshop is. I read somewhere (I think it might have been in reference
to crystal sets) that you can use coax for an AM lead-in. Would this be
better for a longer/more convoluted lead-in? Would I use the braded shield
as the ground connection or would I run a separate ground back to my copper
rod outside? What type of coax would be best for this sort of thing? I am
interested in receiving both broadcast and shortwave. Any info on this
matter would be most appreciated.

thanks in advance,

Dave

Al Klase figured that our several years ago:
http://www.webex.net/~skywaves/ANTENNA/antsys.htm

Jiri Placek
Boyertown, PA