Hints and Tips

LM386 anti hiss modification

The LM386 is a very useful little audio amplifier chip and has proved popular in QRP receivers. It has one draw back, in that it is quite a noisy device. A modification waas described by KA4UOS in Sprat 79, but originally in the Oklahoma QRP Group Newletter. Just two components need to be added, a 10K resistor and a 10n disc ceramic capacitor as shown above. They can often be tacked on on the reverse of a PCB already constructed .(G3YCC)

Front panels for home brew rigs

Instead of using aluminium for the front panel of your new rig you're finishing off, try using PCB material. It is easier to work with, especially when drilling and adding meter holes etc and it takes spray paint well. It is also easy to solder earthy connections to on the inside, like potentiometer connections, bypass capacitors and so on .(G3YCC)

Re-use that Box!

One of the things I found useful over the years is never throw away used metal boxes or cabinets just because the holes are not in the right spot, or because there are too many holes, etc. Cover the box with white formica for a fraction of the cost of a new box. White formica is great for lettering (with transfers) and a dab of finger nail polish keeps the transfers from being scratched off. ( W3RDF)

Antenna Tip

Fishing swivels soldered to the ends of a section of wire serve as "quick connects" enabling you to couple sections together for different bands. Don't depend on the loosly coupled swivels for electrical connections. Make sure you have a jumper with an aligator clip on one end to ensure good continuity. ( W3RDF)

Spraying Front Panels

My favourite spray paint treatment for front panels is to use Ford Graphite 2 - a stage paint. It is comes in two cans, the paint and a clear lacquer. It gives an attractive and hardwearing finish. Remember to prepare aluminium well by cleaning thoroughly and rub the metal surface with wire wool to give a key for the paint. A coat of primer is recommended. There is a special 'primer' for aluminium which is also useful (G3YCC)

A Third Hand

Got a box full of old capacitors? Got one of those oldies with screw terminals on the top? Screw a bull dog clip on one of the terminals and Hey Presto - a third had to hold that PCB, DIN plug etc., whilst you solder it.(G3YCC)

Ugly Style Circuit Boards

If truth be told I am usually building more often than I operate but I don't usually bother with pcb's unless I envisage more than "one offs". Even so, I usually use the very nice and freeware Easytrax PCB program to first lay out the components. My style is then to use a chunk of single sided board, copper uppermost and mount the components ugly style. Leads that don't go to earth, go through to the other side via holes cleared by a veroboard cutter. They then join up underneath, usually by using the component leads themselves with sleeving if required.

By using easytrax first, it ends up not quite so ugly. You can retrieve a copy from the Lehigh archives. i.e. ftp://ftp.lehigh.edu/pub/listserv/qrp-l/tools/easytrax.zip

Easytrax also has the ability to print a "silk screen", so you can use it as a drilling and component placing guide. ( G4WIF)

Another Front Panel Idea

Equipment front panels I do on the computer. We exchanged mail recently about drawing packages. I use Freelance v2 which you can get a rallies for very little. Once the front panel is printed from my old-ish but great little H.P. 520 inkjet printer, I cover it with plastic book covering material. Then I cover the equipment panel with thin double sided sticky tape which holds the printed design in place. Of course if you get it wrong or mess it all up, you have the file on disk to make a new one.

Of course EVERYTHING has an idiot diode built in! (G4WIF)

One Man's Antenna problem Solved

Here is a completely unoriginal idea for a simple multi band wire aerial:-

My garden is a very odd shape and I could not see an easy way of putting up a G5RV or other dipole/doublet arrangement without bending it. I mapped the garden by triangulating it using a tape measure and bamboo for the "surveyors poles". I estimated the height of the house by counting the bricks to the eaves and pitch of the roof. Drew the map on squared paper.

Casting my eye through the ARRL Handbook I saw a design for something called the Loop Skywire. In essence this is a square sided full wave loop at about 40' oriented horizontally and fed by co-ax. I looked at my map and the design, cut a square of paper to scale for a 40 meter square loop and saw that the ends would not be easy to support. I then mocked up a 40 meter equilateral triangle and saw that, if I mounted the Apex under the eaves of the house (About 7 Meters high) I could support the base at about 3 Meters by extending the height of the fence posts by a couple of feet.

I went to the local DIY Shop and purchased 100 Meters of thick twin flex (AKA Bell wire) for, I think 8. Back in the garden I put two canes 13.3 meters apart tied an end of the cable to one of them and measured off 40 Meters (ie 3 Lengths). I then split the 2 wire in to two 40 Meter lengths (Much swearing as it coiled and tangled a lot). I put aside one length for the loop and cut the other one in half to make the feeder. I used scrap plastic book binders (V section, hint attributed to Rev G Dobbs, Practical wireless) for the spreaders, each cut into 6 cm lengths with holes 4 cm apart. Placed these at 30 cm intervals.

Found three brass cup hooks in the scrap bin and a couple of 6 foot lengths of scrap 2x1 pine and a couple of bungee hooks. 1 hook in each piece of wood. Then used said wood to extend fence posts to about 3 Meters. Found a 35mm film canister and some self amalgamating tape. Drinned 4 holes in the canister put the ends of the loop into two, the ends of the feeder into the other two, pulled both through and soldered the ends of the feerer to the ends of the loop. Put the cap on the canister and, after checking the continuity wrapped lots of tape around the canister to make it water tight. Went up stairs to the upstairs bedroom and opened the window. Screwed third cup hook to the wood under the eaves. Then, with much amusement to the next door folks, I used some string to raise the feed point up to the cup hook and tied it on with some nylon wire taking care to relieve the strain. Back in the garden I looped the bungee hooks around the loop and, climbing a ladder, hooked one bungee hook to the cup hook on the each extended fence post. It sagged a bit between the fence posts so I put up a third support. Lastly I pulled the feeder around to the shack and fed it through the window. Without an ATU this antenna gives a low SWR on 80, 40, 20, 15 and 10 Meters. This was checked using my Ten Tec ARGOSY 2 and my Stockton Power Meter. It cost me less than 10 and was fun to put up.(G0XAR )

Getting that nut started!

Can't get the nut on that bolt, deep in the rig? Use a blob of Blutak on a screw driver to temporarily hold the nut and get it on half a turn. (G3YCC)

Panel spraying

My favourite spray paint for boxes, front panels is Ford Two Stage Graphite, consisting of the dark grey paint and a clear lacquer. Add your labels before the final coat of clear lacquer. Don't forget to prepare the surface well before spraying - gentle wire wool treatment is fine. Aluminium is best prepared by using a Chromate priming coat.(G3YCC)

Nut rescue!

I often use one of the old AVO clip type prods to pick up wee nuts & bolts or anything else that may have been dropped into the works of a rig etc.(G3MBN)

Antenna tip

I use a nylon cable-ties (you know, the sort with a ratchet built in), to support the 300 ohm ribbon feeder at the centre insulator of dipoles and such other centre-fed antennas. Simply anchor it to the insulator, and thread the loose end down through a number of the slots. Then bend it back on itself and tape it in place. Self amalgamating tape is good here. They are also useful as cable restraints where it enters/exits a cabinet for instance, such as a mains lead etc.(G3MBN)

Tidy that work bench!

Some plastic freezer packs, or even egg boxes make good bench tidies for preventing loose items from being lost when you are working on some piece of kit.(G3MBN)

Another Tip for Finishing Off that Box!

I often use black Fablon, self adhesive shelf covering material, instead of spray painting. It takes Letraset well and you get a perfect finish which is fairly durable. It also covers a multitude of sins, scratches etc. Unwanted holes from a previous project can be covered by a layer of stiff card board, like one of those useless QSLs we all tend to accumulate! (G3YCC)

Uses for Waxoyl

The use of silicon grease or WaxOyl smeared into the connection box of VHF/UHF antennas will make the screws last for years. Apply with a small kids paint-brush. Also smear some around the lid seal.(G3MBN)

Circuit board idea

P> I have been working on a method of doing printed circuit board prototypes, without any etching chemicals. Sounds crude, but I cut through the copper on the board with knives made from old hacksaw blades. The knives are patterned after Inuit cutting tools, used for skinning seals etc.

If you're only doing one board (like a printed circuit prototype), its really quite quick. I've worked with lots of 14-pin integrated circuits, and even some surface mount components. You can't cut really thin traces used in computer-type boards (where lines are routed between I.C. pins) but for analog circuits, its adequate.( VE3DNL)

Improve that Receiver, Free!

Have a few rigs here with upward pointing speakers as a result you lose power in that direction.

My solution was to buy a 5" dia kids plastic ball, cut in half as accurately as you can and then cut in half once more. sit the result on top of the rig. not only can you steer the audio to where you want it in the shack but it also improves the high frquency response, please try it and let me know what you think .(G4APO)

Printed Circuit Board Tip

Though I mostly construct using "ugly style" (see a previous Hint & Tip) I have been known to make the odd PCB. Instead of the conventional and more expensive PCB pen I use STAEDTLER permanent markers which are usually used on slides for overhead projectors. Use the "fine" type for the tracks and the "medium" sort for filling in large areas that you don't want etched. For even larger areas, such as earth planes, use insulation tape. An additional bonus to using marker pens is that they are easily available in the high street.(G4WIF)

The Bamboo Vertical

An early 1970's issue of 73 Magazine contained an article called "The Bamboo Vertical" or some such thing, which popped into my mind as I read all the posts about vertical antennas and related subjects on the list. The author described a wire vertical dipole taped to a tall bamboo stick supported up high enough to have a clear shot at the horizon. The writer said it was the next best thing to a beam for working DX.

The tuned feeders left at an angle similar to the sloping lower half of the dipole so the feeder would be spaced a similar distance from each leg to keep from disturbing the balance.

My vertical ground plane currently in use is similar except that it has 4 radials for enhanced omnidirectional performance. It is exceptional on low angle paths and DX. It's cut for 20 meters but with the tuned feed it performs acceptably from 40 through 10 meters.

I am thinking of removing 3 radials to slightly increase the feedpoint impedance for an easier match at the tuner end of the feedline, and perhaps enlarging it a bit for better performance on 40 and 30 meters. I think this antenna could easily be taped to a PVC mast for cheap construction and elimination of a dipole windload usually placed at the top of a mast. ( KD0CA)

MFJ Versa Tuner Tip

I just learned something that may be common knowledge to everyone else, but here it is. Messing around with the calibration of a MFJ Versa tuner (949D), I adjusted the trim pots which calibrate the forward and reverse power meters. I was not clear on how to calibrate the reverse power meter so I called MFJ. They said just to switch the tx input cable with the antenna output (which should actually be an external dummy load) and the reflected power meters would then read forward power and could be calibrated using the trim pot accordingly.(KB9KOL)

A Handy Bench Aid

Here's another useful FREE aid from Sprat (of course!), thanks to G0BHI.

Another Front Panel Idea

The technique was as follows:- Use your trusty word-processor to write the legends as required for the panel in question. Do a print-out on some plain paper to check for correct spacing, position etc. When satisfied, print onto white paper, then use a photo-copier to transfer the design onto suitable coloured card. Take this along to your local print/copying shop and have it plasticised, ie given a plastic coating as they do with maps etc. The design is then glued to the front panel using a contact adhesive. Cut out holes for controls, meters etc with a scalpel before mounting same onto the pre-drilled panel.

This method is both inexpensive and versatile in that you may choose any combination of script size and font from your WP. The cost of plasticising an A4 sheet is less than two pounds. It is probably more economical to do more than one layout per sheet, or to make duplicate copies to allow for the inevitable cock-up! (G3MBN)

The Wandering Key Syndrome

As for keeping the key/paddle in one place on the desk (apart from nailing it) I find that a piece of sheet butyl rubber is very good indeed due its tacky properties. If anyone wants some, I can supply it courtesy of a local plastics factory. May I suggest a nominal quid would cover cost, post etc, for a piece say 25 cm square, any excess would go to a charity of my choice.(G3MBN) Email: brian@brimar.demon.co.uk

Solder Storage Tip

I buy solder in half-kilogram reels, because it's much cheaper that way. However, these reels are too large and heavy to hold easily while soldering, so I rewind some of it onto the small reel from the inside of an old 35mm film cassette. This is much more convenient to hold, and lasts several weeks.(G4XVE)

Powering the 49er

Having received my 49er kit from N4ES which he purchased for me at Dayton I wanted to make this the rig of choice for those business trips and vacations. The one problem I sought to surmount was the lack of a easily transportable and replaceable power source. To solve the power source, I took a MAXIM 762 IC and 4 capacitors a diode and a inductor and create 15 volts from two 1.5 volt D cells. This IC is a dc to dc coverter that will create 15 volts dc from 1.5 to 16 volt input source and provide 15 volts output at 150 ma. Just what I needed. Check out the web site ³http://www.maxim-ic.com². The dc to dc converter generates considerable noise so I isolated the power supply from the 49er by a 12 ohm resistor. This worked out fairly will since the transmitter pulled 100 ma and this gave me 1.2 volt drop accross the resistor for 13.8 volts applied to the transceiver. I added the fixes to the output filter on the transmitter side and this resulted in 1 watt of RF drive in! to 50 ohms. Measurements on the receiver indicated that I was able to listen to 10 uV signals. This provides me a transceiver that operates on 2 D cells and should they fail the local drug store or supper market is a ready supply.

The second problem (a small easily deployed highly efficent antenna) has not yet been solved and will continue to be sought after.(KQ4TQ)

Ferric Chloride Staining Tip

Recently I mentioned I had been informed by my domestic manager (XYL), that my nice new shirt had acquired some brown stains. You guessed it, ferric chloride from the latest etching of PCBs! Here is a tip received from New Zealand of how to remove the stain and still retain your marital status:

I would try this.....

Make a strong Citric Acid solution and soak the "spotted" parts with it. eg. 2 - 3 teaspoons Citric Acid to 1/2 cup warm water.

Citric acid is pretty harmless, should be some in the kitchen cupboard !

Let me know how you get on. 73 de Greg, ZL1VGC

Another front panel idea

Empty CD music/data 'jewel boxes' make a nifty cover for most small projects. Cut to size and they will fit most Mono-band transceiver front panels. Nice in as much as they tend not to "droop" or peel like thin guage plastic sheets. I have found a few that are colored amber and even 'smoke' color.

New: US $.50 and may also be found at rallys and swapmeets.

John- N5INZ

Another painting hint

Finishing (painting) enclosures.  I prepair surface, paint with cheap spray
can primer, then paint with cheap spray can paint, put in 250 degree oven for
about 20 minutes, let cool, and paint with cheap clear acrilic spray paint.
 Gives me a hard tough surface.  If using rub-off letters, put letters on
after paint cools, and before clear spray.  Be careful in that the clear
spray will likely melt the letters into the paint somewhat.  Easy and a quick

Bill, K5BDZ   k5bdz@aol.com

Thanks to the above constuctors for passing on their ideas. Please feel free to Email any tips to me, (frank@g3ycc.prestel.co.uk) for inclusion.

Frank G3YCC

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