|
New to Ham Radio?
My Profile
Community
Articles
Forums
News
Reviews
Friends Remembered
Speak Out
Strays
Survey Question
Operating
Contesting
DX Cluster Spots
Propagation
Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers
Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net
|
|
1-4 of 4 messages
|
Page 1 of 1
|
|
Home Brew Lightning Arrestor
|
Reply
|
|
by KE4TQH on January 27, 2002
|
Mail this to a friend!
|
|
Has anyone made or have the plans for a lightning arrestor that hooks to your coax.I heard someone say you could make one using an old sparkplug,and that it worked well.Thanks for any info. or diagrams.etc. for this.
|
| |
|
RE: Home Brew Lightning Arrestor
|
Reply
|
|
by WB6BYU on January 28, 2002
|
Mail this to a friend!
|
Spark plugs were often used with the old open wire lines. It was
relatively easy to insert two of them into a metal plate, spaced
to match the feedline. The plate was then grounded. The spark
gap could be adjusted so it didn't arc over on any band when
running full output.
But, just because many hams did it, doesn't mean it would actually
protect the station from a lightening strike!
There are two types of protection to consider: a direct lightening
strike on your antenna, and static build-up on your antenna.
A simple lightening arrestor won't help much in the first case,
but something with a gas discharge tube might provide some
protection IF EVERYTHING ELSE IS PROPERLY GROUNDED.
True lightening protection is not for the faint of heart. Check the
Polyphaser web site for more information.
Static build-up can create high voltages - enough to arc over
the capacitor in my tuner - even when there is no lightening
present. This is much easier to protect against. Some of the older
receivers used a neon bulb across the input, which would start
conducting at around 70 volts. The spark plugs work on the same
principle, but they will arc at a much higher - and not well
defined - voltage (unless they are just in the receiver circuit, they
must be adjusted so they don't arc over at the peak voltage during
transmit.) Most of the tube radios probably would survive an
occasional 70 volts on the input, but transistors probably won't.
(A transistor is called "the fastest fuse on 3 legs".) The solution is
even simpler than using a spark gap: a large resistor across the
feedline will drain the static charges off before they build up to
a level that can damage solid state equipment. The resistance
should be at least 10 times the impedance at the point where you
put it. If you are using 50 ohm feedline at a low SWR, then a 10K
10W wirewound resistor could be mounted in a PL-259 and
plugged into a "T" connector, with the shell grounded. (It doesn't
have to be a low-resistance ground, either.) For and end-fed wire
or open wire line, where the impedance could be much higher, I
might look for a 47K resistor. (With balanced feedline, use one from
each side of the line to ground.) This resistor won't disipate much
power, but common 1/4 watt resistors are only rated for 250V
across them, so you may need several in series to handle the
expected voltage during transmit.
Since all that is needed is a DC ground, you can also use an RF
choke. If your receiver uses link-coupled coils, it may already
provide a DC path across the antenna connector. But most newer
rigs don't. Most common antenna tuners have series capacitors,
but it is possible to design tuners with a coil across the output, and
these would not need any external resistors.
|
| |
|
RE: Home Brew Lightning Arrestor
|
Reply
|
|
by WB2WIK on January 29, 2002
|
Mail this to a friend!
|
For installation in coaxial cable lines, especially if used at higher frequencies (above 28 MHz), I wouldn't bother homebrewing such an "arrestor," when they are commercially available for reasonable cost and this wheel has already been invented.
Cushcraft, Alpha-Delta and others sell replaceable-cartridge lightning arrestors for installation in coaxial cable lines, using conventional connectors (PL259 UHF and UG21 type N); the advantage of these devices is they are constant-impedance designs that are useful through the VHF/UHF spectrum without introducing impedance bumps, etc. -- thus, they may be simply installed in line, using the connectors you're already using, and won't impact the way the lines or the antennas work.
Homebrewing something using a spark plug or otherwise in a coaxial line could be quite a challenge in terms of connectivity and maintaining a reasonable impedance match, especially if you ever intend to use the device above 50 MHz.
Having said all that, I don't use any such devices at all, since I'm in a "lightning free zone" and haven't even seen lightning in several years! (Lucky.)
WB2WIK/6
|
| |
|
RE: Home Brew Lightning Arrestor
|
Reply
|
|
by VU3PHN on April 9, 2004
|
Mail this to a friend!
|
I plan to add an lightening arrestor in my antenna tower. I know nothing about how to do this. would you please tell me what i have to follow.
Lawrence
|
| |
|
Email Subscription
You are not subscribed to this topic.
Subscribe!
My Subscriptions
Subscriptions Help
Check our help page for help using
Forum, or send questions, comments, or suggestions to the
Forum Manager.
|
|
|
