More Construction Advice

An alternative source of transmitters can be found now that the prices of NEW handhelds have significantly dropped.
There are currently some bargains about, and new ones can be bought for as little as £50.00. Consequently, this has affected the second-hand market, a few years ago we bought 2 small second-hand Icom DJ100s for £30.00 each, so this may be a better route to a quality transmitter with a tone-burst already fitted.

A good source of cheap hand-helds which are just the job for remote repeater jamming purposes are available HERE.

Here is an Alinco DJ100E bought off Ebay for just over £20, it is compact, powerful and robust with a tone-burst and variable output power, a bargain. Now a very stable and versatile repeater jammer can be made for well under £100.

If you discard the battery section, the whole unit is then really quite small. We usually use Yuasa 12 volt jelly cells from B&Q burglar alarms, although for solar powered applications NiMh batteries are superb, or modify a solar powered garden light.

Antenna Length

For 2 Mtrs., a ¼ wave wire antenna needs to be approximately 48.5 Cm long or 19.2 Inches in English! You can coil it or extend it, although as most 2 Mtr repeaters are vertically polarized, best results are obtained from a vertical wire. Experiments have been carried out with long wires, and even a very successful test using a barbed wire fence! This was excellent as the signal appeared to radiate from a large area, although when it rained, and as the barbed wire fence wasn't insulated, it stopped working almost all together!

Audio Sources

Keep it simple at first, an ideal audio source can be found in musical or speaking greeting cards. As you can see, they are small, cheap, and their audio output is just the right level to be connected to the microphone input or either of the featured transmitter boards or a hand held. Throw away the silly button cell, and power it from an AA battery or from part of the device's power source. No more than 1.5 Volts though!

Power Sources

We favour the Yuasa 12 Volt jelly cells used as standby power on burglar alarms, these are relatively cheap, but do not try recharging them with a car battery charger! NiMh batteries are also very good, NiCads are a bit pathetic really as they suffer from the dreaded "memory effect".

Final construction of the bug

A decent R.F. proof housing needs to be used for a device made from a transmitter board, there are some ideal die cast casings in the Maplin catalogue. 

In our original designs, all the components, including the battery, were in the same casing. This was sealed against rain with silicone sealant, with an insulated connector for recharging the battery. This worked quite well until the small amount of gas given off from the lead acid jelly cell whilst charging, started to corrode the tracks on the circuit board!

We now favour the transmitter, audio source, and timers being sealed inside their own waterproof die cast metal casing, with the battery attached to power leads. The Yuasa batteries are quite capable of being exposed to the atmosphere with no detrimental effects, and this design has distinct advantages, we just put a couple of rubber bands round the 2 items.

No possibility of corrosion due to acid fumes, and the batteries are easily changed.

In the past, a well sited device needed to be collected, taken home and re-charged, then replaced in its hiding place. With a separate battery you do not run the risk of being found with the device in your possession either at home, or to and from the site. Thus a possible source of problem is completely removed as you can simply change over the battery as and when it needs replacing. A 15 to 20 second blast every 30 mins usually gives at least 8 days use. It is unwise to regularly change batteries, for example, every Sunday afternoon. It is best to be as random as possible, and even leave a discharged unit for over a week before recovery.

A 1.9 A Hr battery will give at least a full week of 24 Hr. use at our recommended intervals, that is no more than 2, 30 second bursts in any hour. As we have already said, our extensive tests have shown that this gives the required amount of annoyance coupled with a great degree of difficulty for DFers!

For devices made with old hand helds, a plastic case is usually good enough, as the radio has enough R.F. screening in its own case.

One of our most successful campaigns used 3 identical devices, all timed by quartz chiming clock modules, set to go off at 20 minute intervals. The 3 devices were 15 miles or more apart across 2 counties, but still each one was in line of sight to the target repeater, it still bring a smile to my face now, remembering the monitored conversations of the people who spent night after night trying to locate what they thought was just one device.
15-20 seconds an hour might not sound much, but getting a blast of Laughing Policeman Song 3 times an hour really sent some of the straight laced buffoons right to the edge, and whilst they spent every night racing round the countryside in 2 or more cars, we stayed at home in the warmth listening to their fruitless search tactics, very satisfying. 100% success!

Device Locations

Finding suitable locations can be quite interesting. Devices can be placed either in built up areas or in the countryside, ideally, within line of sight of a repeater. They need to be camouflaged to a certain extent to avoid being found accidentally.

We recommend the use of a handheld to test the sites selected. Set your radio for the LOWEST output, we suggest a few milli-Watts, if you can still open the repeater, then the device will as well!

This aspect of the hobby can be more informative, rewarding, and educating than many of the more legitimate pursuits of the cardigan wearing loonies!

Other Possibilities

There are no end of possibilities for the ingenious here. Some very sophisticated devices have been made with digital speech modules, a vast improvement over the original auto-reverse walkman we used in our Mk.3 model!

Technical progress has brought the price of these modules down to just a few pounds, and they have the advantage of non-volatile memories, so they retain the message or music even when the power is removed.

One of our members, who travels the country on business, has a very nice gadget that plugs into the mike socket of the Yaesu radio in his car. It plays small snippets of songs and abuse at random intervals from a neat sound module, and draws its power from the mike socket. Limitations of this aspect of our hobby will only be brought about through your lack of imagination!

Phantom Repeater Fault Module

An interesting and simple device was made by an LPWS member that transmitted only a very low power carrier wave on the repeater input frequency, no sound and no tone-burst. When someone used the repeater, all seemed OK until they stopped talking, the repeater was help "open" by the lower power bug, it then timed out if the other party didn't talk over it.

The power was so low that it was impossible to locate with the repeater's TX signal firing up every few minutes. It was powered by 4 AA rechargeable cells, which gave it a little over a full day's use. The repeater group still have no idea about this device, their reaction was to assume the logic was at fault and constantly take the repeater apart/

The device was recovered every few days, recharged, then replaced. The repeater group then assumed the logic circuitry at fault again, and they spent ages trying to locate the fault. Dead simple, highly effective, and cheap, and they are still none the wiser!

Here is a picture of the actual device

Made from a virtually scrap device bought at a rally for £5.00, subsequent variations have been made just 10% of this size, using the much smaller crystal controlled bugs, the only factor controlling the size being the power source.

Examples of suitable crystal controlled transmitter modules

At this low power, antenna matching is not a problem, in a rural situation you can actually use a length of barbed wire fence, for example, as a long wire antenna. A prototype we tested was constructed in a small black plastic box with just a wire and crocodile clip protruding, this was attached to the fence wire and provided a carrier strong enough to hold the repeater input open, over 2 miles away!

Total cost, under £50, entertainment value £ PRICELESS!