On 12 feb, 08:21, aldg wrote:
I have a Craig CR-4100 radio at my desk at work. It's surrounded by a
metal shelf work on the desk top. As a result, it picks up only 1 or 2
FM stations and no AM stations.

The radio's built-in antennas a

1. Internal bakelite AM antenna with NO external antenna input plug;
and an

2. External (on back of radio) extending metal pole FM antenna with NO
external antenna input plug.

I would like to add an active or passive external AM and FM antenna
that I can set on the top of the desk's metal shelf work and allow the
radio to pull in all the local AM and FM stations.

From the Usenet Newsgroup: rec.radio.shortwave, I would like the
following:

1. A suggestion for an external AM and FM active or passive antenna;
and

2. A wiring diagram that will describe how to install the external
antenna.

Thanks, in advance for your input in this matter.

Al Gershen
Grants Pass, OR, USA

Hello,

For the wiring diagram and instructions, see Brenda Ann's excellent
response.

Regarding diminishing returns, relocate your receiver (or other
receiver) to a place where you can receive the stations you want (both
FM and AM), and that is appropriate to locate your antennas. When you
can find such a place, you can proceed adding the external antenna
inputs.

If you plan to install the antennas outdoor (that means cable will
enter the building from outside), make sure to follow local
regulations on safety (lightning).

For the FM antenna, a straight wire half wave dipole or folded dipole
(with 4:1 balun in it) will be fine if you can receive the stations on
a portable also (at the position of the antenna). Use 75 or 50 Ohms
cable to connect the antenna to your receiver.

For the AM antenna, a large single wire loop (about 1 square meter [11
square feet] may do the job. Also here, use 75 or 75 Ohms cable to
connect the antenna to the receiver. The loop must be oriented
vertically and has maximum reception in the plane of the loop.

If you are in an interference rich environment, you may need to insert
a balun (if not already present in the antennas), to reduce the effect
of interference generated close to the cables and receiver.

Note that antennas exist that may perform better, but complexity
increases more then proportional and success depends on several other
factors. I don't know the quality of the receiver, but using external
antennas may result in bad reception due to strong signal overload.

Best regards,


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me.