Ham To Ham #33 - June 1998

73's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108

USA

E-mail: dmiller14@juno.com

Moderator's note: Roger and Ron Block of PolyPhaser Corporation have put

together a well written series of tips and suggestions on how we can

effectively protect our ham radio stations from the effects of a

lightning strike. Part 5 of that series appeared last month, part 6

follows:

Lightning protection - what your mother never told you! - Part 6

Special installations

Let's talk a little bit this month about high-rise installations. Our

definition of a high-rise building, such as might be used for an amateur

repeater installation, is different from that of a multilevel house,

because the antennas on a high-rise are not on a ground-mounted tower.

Because of this, the single point grounding plan is an absolute must for

any high-rise equipment room. Grounding both the antenna and the single

point system in the equipment room is usually pretty

easy for buildings with structural steel framework ... just bond directly

to the building steel.

Buildings that do not utilize steel construction aren't as simple. Some

high-rise buildings have a fire riser which has a "home run" (direct

drop) to the basement, where a super charger pump is usually located. The

riser may be used as a ground path if the pump's power is properly

protected (3-phase), and a strap jumper is installed to take the strike

energy past the pump's gasket (on both its input and output ports). If

the riser is more than 50 feet away from the

equipment, it may not be the best ground path to use. Check for other

paths such as existing building lightning rods with down-conductors, or

large electrical conduits. Do not use drain pipes or vent stacks. If

these first alternatives are not available (regardless of the path

distance) and it is impossible to run a heavy strap down the side of the

building, then the antenna can not be earth grounded.

When a nongrounded antenna is hit by lightning, the energy will traverse

the coax line to a single point equipment ground location. This may be

many meters away from earth ground, therefore, the inductive/resistive

voltage drop can be very large (hundreds of thousands of volts when

dealing with lightning). The objective then, is to allow equipment to

"float" at high potential. The correct grounding plan achieves a single

point ground with no sneak paths. Sneak paths are loops that allow

lightning current to flow into the equipment room with the objective of

seeking out a "lesser" ground path.

Power safety grounds and concrete floors are the most common sources of

sneak (lesser) paths. A power safety ground can be fixed by adding a

distribution panel and protector at the single point grounding location

for small sites (a plug-in protector grounded on the single point

grounding panel). All I/Os must be protected at this single point.

During a strike, distance equates with the voltage drop to earth, thus

the entire room of equipment will be elevated above ground. Sharp

corners on equipment cabinets can break down the air (ionize the air),

causing current streamers to flow. These will be of very low current

unless an inadvertent sneak path is found by these streamers. Heater

vents and electrical conduits, not grounded to the single point system,

can become such inadvertent paths (unless these vents and conduits are

connected to critical equipment which cannot handle such surge currents

at the lower floor equipment location). It is a good idea to ground (to

the single point), all conductive objects within one meter of any single

point earthed equipment in the room. Dealing with a floating equipment

room requires a slightly different "mindset", and careful inspection and

layout should be paramount in

its protection design.

Tower-mounted equipment is similar to the above high-rise situation. The

I/Os must be safeguarded and the protectors must be located and bonded

together. Single point grounding should be easy to accomplish if the

equipment is mounted inside an approved metal enclosure.

That's Roger's and Ron's presentation for this month. If you'd like to

see the original, unabridged version of this series, you can contact

PolyPhaser Corporation, Customer Service Department, 2225 Park Place,

P.O. Box 9000, Minden, NV 89423-9000 and ask for their Special Bulletin,

"Protection to Keep You Communicating" (copyright 1995). You can also

pay a visit to PolyPhaser's home pages on the world wide web at:

http://www.polyphaser.com/. PolyPhaser's web site also supports text

downloads of the original material that's going to be condensed here,

plus other related texts on the subject. The PolyPhaser Tech Line

telephone BBS at (702)782-6728 is also available to interested readers.

The communications parameters are: Data bits - 8,

Parity - None, Stop bits - 1, Baud rate - 300 to 14400. If you are

dialing in for the first time, the Tech Line requests your name, address

and telephone number. You will also need to create a password. Once

you've logged-on, just follow the menus to navigate around the Bulletin

Board. The Ham To Ham column will continue this series on protecting

your ham station from the destructive effects of a lightning strike with

part 7 coming up next month.

Look for the silver lining

Here's a clever tip from Mike Leahan N9PQK on turning what's normally a

problem, into a solution: "I was in the final stages of construction of

TEN TEC's 2-meter to 6-meter transverter kit when I found myself in

critical need of a signal generator to align the receiver section of the

transverter. Not having a low power 6-meter signal source, I happened to

remember my shack computer, you know, the computer that outputs birdies

right on the frequency that you want it not

to interfere on! If all clouds do have a silver lining, as the saying

goes, maybe I could find one of those birdies on 6-meters to help me

through this particular dilemma.

Sure enough, there, right in the middle of the 6-meter band, was a signal

from my computer that was just the right strength to allow me to peak up

the receiver section well enough to bring its sensitivity up to the point

where I could then leave the final tweaking for a suitable off-the-air

signal later on. The transmitter section tuned up nicely using a VHF

SWR/power meter in-line into a dummy load and I used a VHF tunable

receiver to check for out-of-band spurs, but the

computer (with its plethora of harmonics) saved the day for initial

receiver sensitivity alignment. It's a good suggestion to keep in mind

the next time you need a signal source and haven't a generator available

for that particular band or frequency grouping. Maybe clouds do have

silver linings?"

Think up, not out

Here's a tip from Tom Hart AD1B for getting more milage from your limited

desk or shelf space: "Having a rather compact desk for my ham station, I

have to intergrate new items of equipment somewhat carefully and by using

a bit of "ham inginuity"! Since my mono-band transceivers, and their

associated antenna tuners for 2-meters, 6-meters and 10-meters took up

way too much

precious space when sitting side-by-side, I designed the stacking-bracket

system shown in Figure 1 would be a nice alternative.

I purchased some 1/4" x 2" x 24" oak strips at a local lumber yard to

build the support system. Mine worked out well using 4" strips for the

horizontal pieces and 5" strips for the vertical suppots, but these

dimensions may vary somewhat with difference sizes and configurations of

equipment. In addition to saving that valuable desktop and shelf space,

the stacking-brackets allow items of equipment of very different sizes to

be one-above-the-other and without the

danger of scratching cabinet tops or covering vent holes as might be the

case if the two items were in actual physical contact. The two items of

equipment can also be slid out independently to some degree, which

wouldn't be possible with direct stacking and the bracket's vertical

section can even serve as a nice spot to hand a hand-held microphone.

The time needed to build the stacking-brackets was minimal, the cost

small and the results very satisfying."

Moderator's note: Nice idea, Tom. If you don't want to drill holes in

the sides of the top piece of equipment, you can still use Tom's idea by

making up a bottom board for the top piece of gear, perhaps using two

vertical supports per side instead of one. Figure 2 shows the basic idea

graphically.

Don't pan this idea!

Here's a tasty suggestion from John Nix: "I recently visited a store in

my area that specializes in liquidating damaged merchandise (from

insurance claims salvage, etc.), and my eye was caught by some of the

variety of rectangularly shaped roasting pans that are available today

... for ham radio and electronic use of course!

Years ago, I had thought about mounting a particularly sensitive printed

circuit inside of a cake pan that sported a sliding metal cover ... to

protect the delicate components inside from possible static damage.

Today however, the array of cookery cleverness is even broader, so it may

pay to stop and browse the next time you're in one of the stores that

specialize is kitchenware.

Some of the aluminum roasting pans could easily be converted into an

inexpensive housing for a home-brewed mono-band transceiver, antenna

matching unit, or, fitted with a hinged lid, even a rugged airline

carry-on for your ham rig or lap-top computer. The secret, if that's the

right word, is to try to look at these cooking containers with a

different perspective than what the

manufacturer had in mind when he made them. 'Old fashioned ham

ingenuity' I think it's called.

Cooking containers are usually build very well, to stand up to years of

high temperatures, scraping and washing, and yet they're often priced

very reasonably, because of the mass production and mass marketing of

them ... unlike some of the lower-sales-volume cases that are ordinarily

seen in the electronics parts catalogs and stores.

So I guess the bottom line is this ... the next time you need a sturdy

enclosure for your ham radio or electronic project, take a look in the

cooking section of stores first ... you might just end up with the right

recipe!"

Stamping out twist-ties

I've run into a number of ham transceivers that utilize those metal wire

(encased in plastic) "twist-ties", used to hold bundles of wirs together

within the inter-wiring of the unit. No doubt this shortcut speeds

production, but I've often wondered whether anyone has ever encountered a

short due to the use of these conductive ties (conductive at each end at

least). I've never encountered a problem that I could directly relate to

a short or intermittent attributable directly to the use of these "ties",

but it nonetheless seems a somewhat risky choice for use inside of an

expensive piece of electronic equipment. As I find their presence inside

of ham transceivers and other related gear, I've been replacing them with

either small plastic "zip-locked" cable ties, or with waxed lacing cord

formed into single-loop style of ties. It seems a much better choice and

time well spent if it leads to less potential for problems in the future.

de NZ9E

Murphy's Corollary: A Volt-Ohm-Millampere meter will always be in the

"milliampere" position when a voltage reading is first taken, thus

shorting out the circuit under test and blowing the fuse in the meter.

The only exception to this rule is when the meter has been inadvertantly

left in the "ohms" position, in which case the meter's odd-ball

ohms-multiplier resistor will be destroyed.

Thanks go out to those who've streadfastly supported this column with

their tips, suggestions, cures for our common problems and innovative

ideas ... and especially this month to:

Roger and Ron Block

PolyPhaser Corporation

2225 Park Place

P.O. Box 9000

Minden, NV 89423-9000

Web site: http://www.polyphaser.com/.

Tech Line telephone BBS (702)782-6728

Mike Leahan N9PQK

310 Lincoln Court

Sun Prarie, WI 53590

Thomas Hart AD1B

54 Hermaine Avenue

Dedham, MA 02026

John Nix

9123 Hwy 23 NE

Foley, MN 56329

If you're missing any past columns, you can probably find them at 73's

Ham To Ham column home page (with special thanks to Mark Bohnhoff

WB9UOM), on the world wide web, at:

http://www.rrsta.com/hth

Note: The ideas and suggestions contributed to this column by its readers

have not necessarily been tested by the column's moderator nor by the

staff of 73 Magazine, and thus no guarantee of operational success is

implied. Always use your own best judgment before modifying any

electronic item from the original equipment manufacturer's

specifications. No responsibility is implied by the moderator or 73

Magazine for any equipment damage or malfunction resulting

from information supplied in this column.

Please send any ideas that you would like to see included in this column

to 73 Magazine's Ham To Ham column, c/o Dave Miller NZ9E, 7462 Lawler

Avenue, Niles, IL 60714-3108, USA. We will make every attempt to respond

to all legitimate ideas in a timely manner, but please send any specific

questions, on any particular tip, to the originator of the idea, not to

this column's moderator nor to 73 Magazine.

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