Archive for the 'Antennas' Category

Hoverman TV Antenna

Thanks to the efforts of a great many antenna enthusiasts, the Hoverman design is reborn to help TV viewers obtain off the air (OTA) television signals.

On my hamradio site I document some history, manufacture and testing of a modern version of the venerable Doyt Hoverman UHF TV antenna.

Please enjoy Superbowl TV Antenna.

Magnetic Antennas Work Well on Vehicles

If you are new to ham radio, CB or scanner listening you may have been told magnetic antennas are less efficient than comparable antennas that attach via a direct physical connection.

The answer is… it depends. However, magnetic mount antennas seem to receive more criticism than they deserve and for VHF and higher frequencies the coupling they provide from shield to vehicle body may, indeed, be superior than other mount methods.

The details are available at this article from COSjwt…

http://www.cosjwt.com/index.php?a=3

Read this and know magnetic antennas are a viable option for the CBer, Ham and scanner listener.

J-Poles aren’t so simple afterall

I finally got my copper pipe J-Pole up on a modest mount and cabled into my ham shack. It works, but I stumbled into many interesting things that most folks seem to ignore. In addition to the many J-Pole tutorials on the Internet you should also consider:

Radio Mobile for RF Link Analysis

Here is a great tool for RF Analysis which:

  • Deals with diffraction effects,
  • Computes the Fresnel effects,
  • Handles elevation data from many different sources

RF Links have many issues that plaque all too many folks in charge of ensuring radios work as planned. A tool like this provides this kind of view…

radiomobile.png

With this tool you can understand why some RF links actually fade even when the two antennas are in complete view of each other. When the wavelengths get longer than light wild things happen. The program is free and, from what I can tell so far, works very well.

MFJ Antenna Analyzers

In the past few months I have been testing antennas and antenna ground systems for a series of articles on the main part of this web site…

http://www.cosjwt.com/

One piece of equipment which proved absolutely essential is the antenna analyzer from MFJ Enterprises. I have the older cousin of the MFJ-259B pictured here…

mfj-259b.jpg

Decoupling a J-Pole

When feeding a J-Pole is obviously makes sense to install a choke balun to ensure the outside of the coax shield does not conduct energy down the coax thus degrading the antenna pattern via additional radiator area. This article nicely discusses using beads to achieve the goal:

Ground Rods Don’t Help RF Much

During construction of a vertical antenna in my back yard, I wondered if the popular suggestion that ground rods are essential to good RF performance and antenna efficiency even if you have a system of radials was true.

The answer appears to be no. Visit…

http://www.cosjwt.com/index.php?a=21

…for more information.

Cheap Lightning Protection

Here is a simple way to protect your radio investment from the high voltages induced by lightning activity.

pl259_protector.jpg

Just attach it to your radio and hook the antenna lead to the protector. Ideally you would put this at the entrance to your house or vehicle, but anything is better than nothing. It is a very simple spark gap device which may not protect your radio completely. However, at under $10 it is well worth having at least some peace of mind.

Twin CB Antennas on Trucks

twoantennaslight.gif

Ever wonder why truckers use twin antennas for their CB radio needs? Here is an article which uses simulation to examine the merits and pitfalls of this technique.

Simulation of Two CB Antennas

GAP Titan vs. Reference Monopole

Gap Titan

Here is a good example of a comparison between the Gap Titan antenna and a simple mono-band dipole. While this is yet another A/B test, the author does follow reasonable engineering practices.