SW Receiver - ext. antenna impedance?
 

I have a Grundig YachtBoy SW/MW receiver that I'd like to connect to an
external long-wire antenna, but I'd like to have the antenna on the
roof, while I'd be listening in my office in the basement. I'd like to
make a couple of simple baluns to match it to 75 ohm coax. What's the
impedance that the receiver is expecting? It's just a phono plug
input... Grundig's web site is, ah, not very technical...

--
Jon Gauthier

Given the likely reaction to an increase in
terror-alert level to "severe threat imminent,"
wouldn't a more appropriate alert color be brown?
-Brad Simanek on www.ruminate.com

i think, if there is no koax-input, You don't need a balun. The Grundig
Satellit 600 has both, a 75 Ohm koax- and a high-impedance-input.

greeting Leo Baumann

www.leobaumann.com

On Wed, 19 Nov 2003 16:29:47 -0500, Jon Gauthier
wrote:

I have a Grundig YachtBoy SW/MW receiver that I'd like to connect to an
external long-wire antenna, but I'd like to have the antenna on the
roof, while I'd be listening in my office in the basement. I'd like to
make a couple of simple baluns to match it to 75 ohm coax. What's the
impedance that the receiver is expecting? It's just a phono plug
input... Grundig's web site is, ah, not very technical...

Hi Jon,

The matching doesn't really matter all that much for a receiver,
unless it is through an antenna tuner (quite useful even for casual
SWL). This cuts down on intermods and desense caused by local AM
stations (you would be surprised how much they can hammer your DX
without being heard).

On the other hand, the advantage of coax (50/75 Ohm) is in isolating
the noisy environment of the home from the signal path by allowing the
antenna to be remote. Using a feedpoint choke insures that noise does
not get into the picture. That choke can be in the form of 6-10 turns
of coax in a 4-8" diameter, or using a HAM 1:1 Current Balun
(generally 10-25 ferrite beads that fit over the jacket of the coax
cable at the feedpoint end OR the coax wound through a large ferrite
torus 3-5 times).

73's
Richard Clark, KB7QHC

Thanks, Richard - I'll give it a try.

Richard Clark wrote:
On Wed, 19 Nov 2003 16:29:47 -0500, Jon Gauthier
wrote:


I have a Grundig YachtBoy SW/MW receiver that I'd like to connect to an
external long-wire antenna, but I'd like to have the antenna on the
roof, while I'd be listening in my office in the basement. I'd like to
make a couple of simple baluns to match it to 75 ohm coax. What's the
impedance that the receiver is expecting? It's just a phono plug
input... Grundig's web site is, ah, not very technical...


Hi Jon,

The matching doesn't really matter all that much for a receiver,
unless it is through an antenna tuner (quite useful even for casual
SWL). This cuts down on intermods and desense caused by local AM
stations (you would be surprised how much they can hammer your DX
without being heard).

On the other hand, the advantage of coax (50/75 Ohm) is in isolating
the noisy environment of the home from the signal path by allowing the
antenna to be remote. Using a feedpoint choke insures that noise does
not get into the picture. That choke can be in the form of 6-10 turns
of coax in a 4-8" diameter, or using a HAM 1:1 Current Balun
(generally 10-25 ferrite beads that fit over the jacket of the coax
cable at the feedpoint end OR the coax wound through a large ferrite
torus 3-5 times).

73's
Richard Clark, KB7QHC

John,

A single wire is going to have a huge variation in impedance over the 5 - 30
MJz range. You are much better of with a fan type antenna that has multiple
dipoles, all tied together at the feedpoint. I saw one of these in a ham
catalog, but can't remeber where. For a compromise, I would cut dipoles for
6.5, 11, and 16 MHz. Tie them together at the feedpoint, and fan out the
ends. You don't really need a balun, but if you want to, use a 1:1 with
either 50 or 75 Ohm coax. The length of eacch dipole in feet is 468/MHz,
half of that length on each side.

Tam/WB2TT
"Jon Gauthier" wrote in message
...
I have a Grundig YachtBoy SW/MW receiver that I'd like to connect to an
external long-wire antenna, but I'd like to have the antenna on the
roof, while I'd be listening in my office in the basement. I'd like to
make a couple of simple baluns to match it to 75 ohm coax. What's the
impedance that the receiver is expecting? It's just a phono plug
input... Grundig's web site is, ah, not very technical...

--
Jon Gauthier

Given the likely reaction to an increase in
terror-alert level to "severe threat imminent,"
wouldn't a more appropriate alert color be brown?
-Brad Simanek on www.ruminate.com

I have a Grundig YachtBoy SW/MW receiver that I'd like to connect to an
external long-wire antenna, but I'd like to have the antenna on the
roof, while I'd be listening in my office in the basement. I'd like to
make a couple of simple baluns to match it to 75 ohm coax. What's the
impedance that the receiver is expecting? It's just a phono plug
input... Grundig's web site is, ah, not very technical...

Forget the balun and other matching devices. While trying to cover a wide
frequency range it is a waste of time. There will be more than enough
signal for receiving without any matching devices.

Usually, it is best to work for best signal to noise ratio. A way to do this
is to use an "antenna tuner" or "match box", and adjusting for best signal.
Some type of antenna swr or z-meter will give the impedance the receiver
sees- it's usually not a matched condition.
w4mb