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cost A high grade 0f this type of protector that has higher current pro-
tection and built-in telephone line protection is also commonly available
at much higher cost Some companies like Polyphaser and Brickwall
offer surge protection with much improved performance.
There are two main types of surge protectors:
. One type of protector dumps surge current into the SPGP via the
use of Metal 0xide Varistors (MOtf . This type requires an excellent
ground installation with wide grounding straps. lf y0u use this type of
system to dump current into the neutral conductor of the house wiring,
it will not perform well due to the very large inductance encountered in
the path to ground, This type of protector is only limited by the size of
the MOV devices being used and the quality of the external grounding
system. Mov devices can fail under extreme surges,
o The non-MOV type circult that uses a large inductor t0 stop most
surges and dumps excessive current progressively into a bank of
capacitors, Typical circuits for this type of protector can be found in TCA
Hotlink, 11. They can be mounted directly on the SPGP for convenience
but do not rely on the SPGP for protection. This protector is limited by
the amount of capacitance used to store the surge current, These units
are not likely to fail since they do not contain MOV devices. However,
they do contain switches and other components.
The decisron about which type to purchase is not easy. lf you live in an
area which is not prone to lightning storms, a very high quality computer
grade protector will probably suffice. However, if Iightning js a real
problem, you should select a high capacity MOV type or the non-MOV
type as described above, lf your ground system is not ideal due to the
location of the radio with respect to the ground, it is best to use the
non-MOV type circuit as that type does not rely on dumping large
amounts of current into the ground,
Coaxial Type Protectors
There are three basic types of coaxial surge protectors: the dc-blocked
high-pass filter, the dc-blocked quarter wave siub and the straight gas
tube (SGT),non-dc-blocked.
The Straight Gas Tube (SGI) (Non-D0-Blocked)
The SGT consists of a gas tube connected across the coaxial cable.
When the surge voltage exceeds a certain level (around 200 Volts for
low power applications) the gas tube fires and shorts out in a fail safe
mode. The tube must then be replaced, The characteristics of the SGT
are:
. There is no attenuation of lightning frequencies (20 Klz to l MHz)
. The SGT is inherently wide band.
. The SGT might not protect the receiver if the maximum acceptable
input voltage of the receiver is lower than the SGT firing voltage. This is
difficult to check as most amateur radio transceivers do not include the
maximum allowed input voltage in the specifications
The Quarter Wave Stub (DC-Blocked)
The quarter wave stub is simply a shorted stub connected in parallel
with the transmission line. Hence, it has excellent low frequency proper-
ties while appearing as a low loss band pass filter at the desired oper-
ating frequency. lts characteristics are:
. The device is narrow band (approximalely 20% band width)
. The device is passive so there are no components to change rn
case of large surges. lt will not normally fail, even in extreme conditions.
o lt filters out lightning frequencies,
The High-Pass Filter (DC-Blocked)
The high-pass filter type consists of a shunt connected inductor and a
series connected capacitor to form a high-pass filter. lts characteristics
are:
o lt filters out lightning frequencies and is desrgned to do so in an
optimum fashion. The Polyphase DSX model attenuates lightning frequencies
by 89 dB. The quarter wave stub attenuates lightning frequen-
cies by approximately 55 dB.
. The device is passive so there are no components to change in
case of large surges. lt will not normally fail, even in extreme conditions.
Other Configurations
This article discussed the basic set-up which consisted of a single
coaxial cable feeding an antenna that was mounted on a grounded
tower. There are many other arrangements that are often used, Some
systems have a low noise amplifier mounted at the top of the tower
where power must be fed to the amplifier. ln this case the coaxial surge
protector will be mounted at the top to the tower between the antenna
and the amplifier. 0ften, there is an antenna rotator mounted at the top
which requires DC power. The cables that feed the power to the rotator
must also be protected. These and other configurations are discussed in
TCA Hotlinks I -5
An inverted V GSRV or dipole antenna will use a Balun that is mount-
ed at or near the antenna feed point. ln this case the coaxial surge
protector will be mounted on the SPGP
A vertical antenna with ground radials can be set up in the same way
as the tower mounted system. The coaxial cable is first connected to a
single grounded feedthru and then to the house panel as described
above,
A Common Pitfall
An amateur who is using a non-protected system, disconnects his/her
expensive transceiver from the antenna coaxlal cable and places the
cable on the floor of the radio shack when a storm is approaching. This
simple act violates safety guidelines that have been given to us by oro-
fessionals. Here is what can happen. The storm can cause an arc 0n
the lpen ended coaxial cable in the han shack, create hot plasma in
the room and possibly set fire to the house.
Further Study Using TCA Hotlinks
Further information is provided via TCA hotlinks which are easily
accessed via the RAC website. For this information, please visit http:i/
www.rac.caltca. Hotlinks make it unnecessary to type URL addresses
into your computer and provide you with calculators and other support
that demonstrates the ideas presented in the articles. The following
hotlinks for this article are available on the RAC site.
TCA Hotlink, 1 PolyPhaser Technical Literature
htto ://www. oolvphaser. com/
TCA Hotlink, 2 An overview of Lightning Protection for Ham Radio
Stations
http://www. polvphaser.com/NR/rdonlvres/C1 565001 -FB1 A-4AC2-
\.lO QCWAJournal . Wlnter 2aO7 t wwwqcwa.org