Whichever way you go, be sure to put a lightning arrestor on the lead in.
David Forsyth wrote:

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






--
Joe Leikhim K4SAT


"Jazz is not dead. It just smells funny." -F.Z.

If the antenna is the typical end-fed wire then the impedance will be
very high. Most AM radios have a high impedance input designed to
match a random wire like that. If you use coax, the capacitance of the
coax (center conductor to shield) will essentially short most of the
signal to ground and little will get to the receiver. If you've ever
opened up the coax used on car radios you'll find that it is a special
high impedance coax. A small wire fits loosly thru an insulated tube
with the shield around the outside. This keeps a relatively large
spacing between the center conductor and the shield in order to
minimize capacitance.

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

Thanks for all who responded thus far (and sorry to be such a wellspring of
newbie questons).

Yes, I must confess that there is no lightning arrestor installed as of yet!
I was aware that one should install such a device at the time I put up the
antenna, but I didn't have one handy, nor did I feel the need to invest in
one. I was thinking that in the late fall/winter we really don't get any
lightning here (north-east PA) and therefore I wouldn't really need a
lightning arrestor until the Spring. I'm sure I'm probably wrong on this,
though, as it was mainly a product of my Scots heritage getting the best of
me.

I guess it would be helpful to include some more specifics about what radios
Im trying to feed with this antenna. Thus far, I have accumulated an
A****er Kent "big box" Model 20, an A****er Kent 55-C (chassis only), an
RCA Radiola 18, and a homebrew regen. This is my latest project.

It uses a '36 screen grid tube as detector and a 6F8G as dual-stage audio
driving a loudspeaker through an overly large Hammond OPT. So far I've only
wound a coil for BC band and this thing works amazingly well. I plan on
making some smaller coils for short wave (hopefully the solar storm stuff
wont be long in staying).

I also have future plans for a Grigsby-Grunow that was given to me to fix
up, but it's on the distant horizon as of yet.

So far nobody has complained about the large pile of radio-related crap in
the sun porch, but Im sure it's a matter of time. I will probably have to
route the antenna lead-in through a wall or two and around some bends and
twists to get it into the workshop in the basement. I guess I was assuming
I should use coax for this, but apparently not, from what everyone here is
saying. I'm not as concerned about noise as I am about possible signal
loss. Is this something to even be concerned about with a plain old
insulated stranded wire lead-in routed through walls and such?

I'm still new at this RF stuff (being a relatively recent convert from the
realm of "AF"), so please bear with me, and thanks for all the helpful tips
and suggestions!


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

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

"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