Questions & Answers

Q: Can I use a simple ground plane antenna cut for the 2 meter band with my 70 cm radio?  The 70 cm frequencies

are about thre times the 2 meter frequencies - an odd multiple.  It seems similar to using a 40 meter dipole on 15 meters.

A: Yes it can, although it does have some limitations.  I've used a 1/4 wave 2 meter magnetic mount antenna

successfully on 70 cm.  The main lobe moves from close to the horizon at 2 meters to 41 degress up on 70 cm.  On

the low end of the 70 cm band the swr is better than 2 meters.

Q: I am considering purchasing a dual band antenna for 2 meters and 70 cm, but am puzzled as to which type offers a

better performance.  Does a J-pole provide better performance than a ground plane or vice cersa?  I plan to mast mount

my antenna at a heith of 25 feet.

A: Either arrangement will be effective, although the j-pole antenna does have an advantage over the ground plane

of about one db.

Q: Besides the spelling what is the difference between diplexers and a duplexer?

A: Diplexers are passive filtering system that split a wide band of frequencies between two orts based on frequency. 

Unually the ranges are relatively wide, such as a diplexer to allow both 2 meter and 70 cm signals to use the same

antenna.  It might have a split frequency of 300 MHz.  Note that some systems with more than twon ports are

encountered.  They are called tri-plexers for three ports, or the more general multiplexers if more than three.

The term duplexer refers to a special case of a diplexer designed to sharply filter out a relatively narrow band signal

while passing a signal at a relativley close frequency spacing without attenuation.  This is typically encountered in

repeater systems in which the same antenna is used for simultaneous reception of a signal and transmission of another

signal only 600 kHz away.  For example... 145.29 & 144.69.

Q: I am considering buying a conversion van that has a fiberglass rood.  Would it be possible to create a usable

UHF/VHF ground plane by guling mylar, aluminum or orhte foil underneath the roof?  I would like to mount my mobile

antenna on the roof if it will work well.

A: I am not sure if the mylar is really conductive and connectable, however, aluminum or copper foil should be fine

in both regards, althouogh not necessarily easy to use and install.  The key is to be able to connect to it.  If you are

feeding a vertical monopole, it is important that the shield connect to the ground right at the feed point, so you would

have to have a hole in the roof at the base and devise a connection method - perhaps a clamping arrangement - that

would connect to the foil without tearing it.