RadioBanter - View Single Post - Newb Question

Telamon · September 22nd 06, 11:16 PM posted to rec.radio.shortwave

In article om,
wrote:

* Use a Balun with a Dipole Antenna Another 'improved' Shortwave
Listening (SWL) Antenna design would use a Balun {Matching
Transformer} between the Dipole Antennaand the Coax Cable
feed-in-line. This is most often a 4:1 {Four-to-One} Matching
Transformer. Using the Balun will better 'match' the Dipole Antenna
to the Coax Cable feed-in-line and the Receiver across a wide
frequency range then simply using a Dipole Antenna that is directly
connected to the Coax Cable.
- - - The direct conneted Dipole Antenna is great for Hams
working on a single Shortwave (HF) Frequency Band.

This BALUN information is incorrect.

It's this balun similar to the ones used to connect 75ohm coax to the
screw connects on the back of a TV?

The dipole antenna is around the 72 ohm mark, which will vary with
height but is close enough that the BALUN is not needed. If you want to
improve the match with a BALUN you will need a fractional two core unit
to achieve this transform.

A better antenna in the same space would be a folded dipole, which would
use the common and cheap 4:1 transform used with FM and over the air TV
antennas.

If you are going to used a made for TV unit some do not work well at 3
to 30 MHz. Generally look for a unit with more heft due to the more
massive core inside. The units that do not work well from 3 to 30 MHz
use a capacitive matching circuit with a smaller core.

--
Telamon
Ventura, California