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

David Forsyth wrote:
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?

Not necessarily. If you need shielding for noise purposes that might be
worthwhile but apart from that there's no advantage over just a single
wire. The radios you're typically working on have high impedance inputs.

In a random-wire installation, the total length of the wire IS the
antenna. There is no lead-in per se. By using a shielded cable you are
effectively shielding that portion of your antenna. I think you might
find it won't work as well on BCB with the shield grounded and you would
have to lift that at the radio end negating having it there in the first
place.

On shortwave freqs the loss of the cable in a mismatched state such as
feeding a random wire (or an old hi-z radio) may also work against you.

I'd go with the plain wire unless there is a noise problem that is being
picked up by the vertical portion of the antenna.

My 2c.

-Bill

--exray-- wrote:

I'd go with the plain wire unless there is a noise problem that is being
picked up by the vertical portion of the antenna.


Being a smarter than average bear (my own opinion of course :~) I
figured I'd use coax to bring my long wire antenna into the house, and
I'd ground the shield.

Didn't work very well.

Now I'm just using plain wires for each of the antenna and ground and it
works very well. I'd say that my antenna outside the house is about
10-15' off the ground and runs for about 100' in a 50' x 50' "L" shape.

--
regards from ::
John Bartley
43 Norway Spruce Street
Stittsville, Ontario
Canada, K2S1P5
( If you slow down it takes longer - does that apply to life also?)



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--exray-- wrote:

I'd go with the plain wire unless there is a noise problem that is being
picked up by the vertical portion of the antenna.


Being a smarter than average bear (my own opinion of course :~) I
figured I'd use coax to bring my long wire antenna into the house, and
I'd ground the shield.

Didn't work very well.

Now I'm just using plain wires for each of the antenna and ground and it
works very well. I'd say that my antenna outside the house is about
10-15' off the ground and runs for about 100' in a 50' x 50' "L" shape.

--
regards from ::
John Bartley
43 Norway Spruce Street
Stittsville, Ontario
Canada, K2S1P5
( If you slow down it takes longer - does that apply to life also?)



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

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.

Bob, is this something I could possibly be able to use in this application?
Where does one find such high-impedance coax? As an alternative, would it
be possible to put an active device up near the antenna that would act as a
buffer to feed a low-impedance line?

Dave


"Bob Lewis (AA4PB)" wrote in message
...
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.

David Forsyth wrote:
Bob, is this something I could possibly be able to use in this application?
Where does one find such high-impedance coax? As an alternative, would it
be possible to put an active device up near the antenna that would act as a
buffer to feed a low-impedance line?

Dave

The trick in this recommendation is that the car radio feedline is a
specific length (a few feet)and its capacitance is taken into account.

-Bill




"Bob Lewis (AA4PB)" wrote in message
...

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.

David Forsyth wrote:
Bob, is this something I could possibly be able to use in this application?
Where does one find such high-impedance coax? As an alternative, would it
be possible to put an active device up near the antenna that would act as a
buffer to feed a low-impedance line?

Dave

The trick in this recommendation is that the car radio feedline is a
specific length (a few feet)and its capacitance is taken into account.

-Bill




"Bob Lewis (AA4PB)" wrote in message
...

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.

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.