Note: If you would like a copy of any of the circuit diagrams or figures referred to in

this column, simply send a SASE to Ham To Ham Column, c/o Dave Miller NZ9E,

7462 Lawler Avenue, Niles, IL 60714-3108 and indicate the month and circuit or

figure name on your request. No requests will be honored without a self-addressed and

adaquately stamped envelope (SASE).

Ham To Ham #25 - October 1997

73's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108

USA

E-mail: dmiller14@juno.com

For better battery behavior

Here's a tip from 73 author J. Frank Brumbaugh W4LJD that parallels his article on Gel Cell

batteries presented in the February 1997 issue of 73 Magazine entitled "The Gel Cell Storage

Battery (A great little power supply)": "Here's a very simple way to keep tabs on your Gel Cell

battery when it's powering a QRP rig, emergency set-up, field day station, etc. It's an inexpensive expanded-scale charge-status-meter that can be left connected across the Gel Cell during the entire time of operation, since it draws only microamps from the battery that it's monitoring. Figure 1 shows the easy-to-reproduce circuit in schematic form. The actual part values will depend upon what your own 'junk box' yields, what might be obtainable at the next hamfest, or which surplus outlet (hopefully a 73 advertiser) you might tap for the least amount of cash outlay on your part.

M1 in the schematic is a surplus microammeter, which may be 50uA, 100uA or 200uA full scale,

whatever you can find. The smaller the full-scale reading of the meter, the less current will be

drawn from the battery you wish to monitor for a given mid-scale reading. D1 can be any garden

variety silicon diode (such as a 1N4001, RS #276-1101). It's main purpose is to prevent any

possible damage if you happen to inadvertently reverse the plus and minus input leads. ZD-1 is a 1N4739, 9.1-volt, 1-watt zener diode (RS #276-562). Any combination of lower voltage zeners in series, that adds up to about 9.1 volts, will also work. Due to the extremely low current drain, the wattage rating of the zener diode is not particularly important. R1 is an inexpensive 'set and forget' trim pot, whose value will be dependent upon the actual sensitivity of the final meter that you might end up with. For a 50uA meter, R1 can be a 100K ohm trim pot (RS #271-284). Just wire everything in series, with the polarities shown as shown in the schematic, and you're all set.

As mentioned before, this is basically an extremely low-drain, expanded-scale voltmeter circuit.

Anything over about 9-1/2 volts will give you a reading, and you can place the meter's needle

wherever you'd like it to be on the meter's scale, by using the trimpot. You can mark the meter's scale with actual voltage figures, or simply with an 'OK range' and a 'STOP range'.

If you intend to treat your 12-volt Gel Cells with the care and respect that they deserve, 11.5 volts is generally the point at which you'll want to stop discharging them, and this simple metering circuit will tell you when to do it."

Moderators note: Nice idea for a handy battery monitoring circuit, Frank. By the way, you can

modify the circuit to accommodate any battery voltage that you'd like to monitor (6V, 9V, etc), just

by altering the choice of zener diode (ZD-1) in Frank's schematic. Choose a zener diode (or combination) whose zener-voltage rating is a volt or two below the stop-discharge-potential of the battery pack that you're using. Everything else should stay pretty much the same.

More power to you

Stephen Reynolds sent in this idea from his own recent experiences: "I've always wanted a

dedicated power feed into my ham shack, but my power service panel wouldn't support the

needed breakers and capacity. It would have been possible to have a new power service

entrance panel professionally installed, of course, but that was beyond what I wanted to allocate

from my already limited 'ham budget'.

A previously unseen opportunity presented itself, however, when our electric stove finally gave

up and we decided to replace it with a gas unit instead. I now had a 240 volt, 40 amp circuit on

my current fuse panel that was available for other usage, namely my ham station! I ran #8

gauge wires to a new sub-panel in my shack, being careful to follow all of the electrical codes

for my area, and I now have plenty of power conveniently available for just about anything

imaginable, of either a 240 volt or 120 volt nature.

If your own fuse service panel is currently filled to capacity, and you have an electric stove,

electric clothes dryer, or electric water heater, you might be able to utilize any of those circuits

for you ham shack simply by replacing that older electric appliance with a new gas fired model

without the extra expense of a whole new entrance panel. Be familiar with, and always follow

your own local electrical codes to the letter, if you decide to implement this idea yourself. And

seek out the help of a licensed electrician if you don't have the experience or inclination to do-it-

yourself. Now where did I see the ad for that super-duper linear amp?"

Moderator's note: As Stephen mentioned, don't involve yourself with your home's 240 volt AC

service unless you're absolutely confident that you know all of the proper procedures for dealing

with that level of electrical power. 240 volt AC is deadly!

Plug potpourri

Here's an easy-to-apply tip from David Hyman KB0ONF: "If the AC power cords in your ham

shack, computer station or test bench seem to be a jumble of unidentifiable cords and plugs,

you're not alone. Here's an idea that you might try to at least put some measure of order back into that maze of plugs.

Place a small square of white vinyl tape on each plug, and mark the tape with an easily-read

identifier, such as the type number of the item of equipment that it powers. Make sure that when

the plug is inserted into its socket that the tape will be in a position that's readable ... since most

plugs are polarized these days and they can only be inserted one way (see Figure 2). Also be sure to use vinyl tape, because it tends to be more compatible with the rubber or plastic surface of the typical AC plug than other varieties. Vinyl tape is generally available at automotive supply stores because it's been shown to hold up against the rigors of an automotive environment better than others, and it will do the same behind your operating table or test bench."

Moderator's note: The white vinyl tape that David suggests can be written on using a sharp-

tipped, indelible marking pen such as the Sanford "Sharpie" (reg. trade mark) No. 37000 Ultra

Fine Point permanent marker. If there isn't enough room on the tape for a full identifier, you can

simply use a single number as shown in the sketch in Figure 2. Make the number large enough

to easily read and "perfect" enough so there's no mistaking what it says. Now make up a list on

a card or sheet of paper that identifies each number with the item of equipment that it represents.

Keep that card somewhere handy so that you'll have it when you need to ferret-out a particular

plug for removal. A good idea from KB0ONF.

Tight fit

William Thim N1QVQ offers this bit of sage advice: "Mobile antennas that screw into their

mounting base, often have a tendency to loosen up over time. If your antenna's manufacturer

hasn't supplied some type of locking washer for use between the antenna radiator and the

mobile mount, then you might consider backtracking and installing your own. The "wavy" washer shown in Figure 3 works nicely, applying pressure between the radiating element and the mount itself at several points around it's perimeter. You should be able to locate these washers, at your local hardware store or home center. One (or even two) will usually pretty well guarantee that your mobile antenna will stay good and tight in its mounting ... if the antenna is snugged-down correctly to start with. In place of the "wavy" style of washer, you might be able to use one of the older split-ring type of lockwashers, though the split-ring types only provide one primary point of pressure per mating surface (top and bottom).

Whichever lockwasher system you choose, make sure that the metal that it's made of is

compatible with the metal used in your particular mobile antenna and mount. Electrolytic action

between dissimilar metals can often defeat any gain made by keeping the mounting tight,

especially in areas of high humidity and/or salt air, such as might be encountered along coastal

areas. Also recheck your SWR after adding any lockwashers to a VHF or UHF antenna to make

sure that it hasn't changed appreciably, trimming the radiator's length slightly if necessary."

Moderators note: I've experienced the antenna loosening that Bill mentions on my own mobile

installation. I have the feeling that it's probably due to a combination of road vibration and wind

against the antenna, along with the continual changes in temperature that our mobile antennas

are subjected to in their external vehicular environment. The result of course is that, over the

course of time, the antenna radiator can make poorer and poorer contact with its screw-on

mounting stud, leading to intermittent and unpredictable signals on both receive and transmit. In

the worst of cases, the transciever's finals could even be damaged by the quickly varying loads

reflected back into the radio. Bill's solution is a good one, along with routinely checking the

tightness of the antenna in its mount as a regular maintenance item. A coat or two of your vehicle's touch-up paint around the mobile mount-lockwasher-antenna joint will also help to protect against weathering and electrolytic action, as well as serving as a visual indication of loosening if the paint shows any significant fracture lines.

Murphy's Corollary: Feeling completely satisfied is generally a strictly temporary aberration.

That's it for this month and the first column of our 3rd. year on the pages of 73 Amateur Radio

Today Magazine. Many thanks to all of those who've made contributions to the column in the past 2 years, and as always, to those who've sparked the ideas featured in this month's edition, including:

J. Frank Brumbaugh W4LJD

P.O. Box 30

c/o Defendini

Salinas, PR 00751

Stephen Reynolds, N0POU

510 S. 130 Street

Omaha, NE 68154

David Hyman KB0ONF

1455 Edgcumbre Road

St. Paul, MN 55116

William Thim, Jr., N1QVQ

50 Miller Road

Broad Brook, CT 06016-9676

Also, be sure to check out the Ham To Ham column's home page 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.