~Handie Talkies~
This page is written to educate
radio
operators on the effieciency of handie talkies.
Most handie talkies put out no more then 5 watts, some far less.
The antenna on a handie talkie is a compromise antenna. Try this
visual
test... a dipole antenna for 146 MHz is 3.2 feet long.
Lay a yard stick down on a table. Lay your HT beside it, with
the
antenna connector at the 18 inch mark.
The dipole antenna (3.2 feet long) has "unity" gain, i.e. zero
gain. 5
watts in and a very short coax will probably result in nearly 5
watts
effective radiated power.
You can see that the antenna and the body of your HT are far
shorter
than the yard stick. (Yes, the body of the HT is part of the
antenna
system.)
There is no way your HT will be as effective with it's rubber
duckie
than if it had a dipole antenna connected. In fact, your ERP may
be far
less than the HT's rated 5W output.
Rubber Duckie Antenna Facts: (some of this information taken
from
http://en.wikipedia.org/wiki/Rubber_Ducky_antenna
Most handie talkie antennas are some type of spring encased in a
rubber
coating. In fact, once the rubber is remove, what you have left
is a
spring.
If the coils of the spring are wide (a large diameter), relative
to the
length of the array, the resulting antenna will have narrow
bandwidth.
Conversely, if the coils of the spring are narrow, relative to
the
length of the array, the resulting antenna will have its largest
possible bandwidth.
If the antenna is resonant, and the spring has a large diameter,
the
impedance will be well below 50 ohms, tending towards zero ohms
with
large inductors as the structure starts to resemble a
series-tuned
circuit with little radiation resistance.
If the antenna is resonant, and the spring has a small diameter,
the
impedance will increase towards 70 ohms.
Therefore, from these rules, one can surmise that it is possible
to
design a Rubber Ducky antenna that has about 50 ohms impedance
at its
feed-point but a compromise of bandwidth may be necessary.
Modern
Rubber Ducky antennas such as those used on cell phones are
tapered in
such a way that few performance compromises are necessary.
At 70 CM (UHF) frequencies, a quarter wave antenna (1/2 of a
dipole) is
6 inches. Most HT's with 70 CM have a 6 inch antenna on them.
BUT...
most of those HT's also have 2M (VHF) in them.
Therefore, where does the rubber duckie actually radiate? Even
if it is
some kind of hybrid antenna, the radiation efficeiency is going
to be
less than the 6 inch 1/4 wave antenna.
And, if the rubber duckie is actually an antenna made for 2M
(NOTE:
most 2M antennas will show a perfect match on 70 CM) then the
radiation
pattern for 70 CM is going to be so skewed that
the effectiveness goes down the tubes.
So, what can a HT be used for?
If you are line-of-sight of a repeater then you can probably use
it. If
it is line-of-sight and not too far away.
If you are in a hole or dip, your HT is probably better off
being used
in monitoring or paper weight mode...seriously... unless..
You decide to use an external antenna.
How do you pick the external antenna? Buy the antenna that will
give
you the most gain, and keep the coax short. A 6 db gain antenna
with 5
watts input through a short coax will yield about 19 watts ERP.
You can also build an antenna! Do a Google search for "ground
plane antenna", "j-ole antenna" or even "home made beam
antenna".
And here is something to think about on cable loss:
CABLE | LENGTH (ft) | LOSS | PIN (W) | POUT (W) |
RG-213 | 100 | 2.61 dB | 5 | 2.7 |
RG-213 | 50 | 1.3 dB | 5 | 3.7 |
RG-8 | 100 | 2.34 dB | 5 | 2.9 |
RG-8 | 50 | 1.17 dB | 5 | 3.8 |
RG-8X | 100 | 4.0 dB | 5 | 1.9 |
RG-8X | 50 | 2.0 dB | 5 | 3.2 |
RG-58 | 100 | 5.0 dB | 5 | 1.5 |
RG-58 | 50 | 2.5 dB | 5 | 2.8 |
So, if you buy a 6dB gain
antenna, add 50 feet of RG-8 cable, feed with 5 watts, you will have an ERP of
about 15.2 watts.
So, the next time you try to hit that distant
repeater while
sitting in
your car under it's "Faraday Cage", and you think your HT is
broke (or
worse, the repeater is screwed up) remember
your HT is a compromise. It will not do the unreasonable....