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What Is A REPEATER?

What is a repeater, well we all know but it is obvious that many people are unaware of what a repeater is and what it does.

Basically, it is a receiver and transmitter usually mounted at an elevated position, to enable communication over a greater area than simply station to station.

ALL repeaters in the UK are privately owned and funded and are freely available for anyone to use, despite what so of the "repeater groups" think. What happens is a group get together and buy or build the required equipment, find a suitable place to mount it, and get the necessary permission from the property owners, plus get a power supply to run it.

A repeater is an automatic device that when it receives a signal on one frequency, will automatically re-transmit it on another. In the past, repeaters were activated by sending a 1750KHz tone, some still respond to this, but nowadays it is more common to use CTCSS tones that seamlessly activate the repeater when you wish to use it.

As most 2 Metre and 70 Cm radios are fairly limited in range, repeaters are found at almost 30 - 40 mile intervals. So called "Short Wave Listeners" monitor repeaters as do the majority of active radio amateurs, standard practice is to call for a contact on the repeater, then go and find a free frequency, although there is no reason not to continue on the repeater if it takes your fancy.

As you can imagine, repeaters are where the fun is and have long been abused with all manner of devices and just simple mucking about and playing music. On the repeater you have the biggest audience, so naturally that is the place to play.

Repeater abuse has been tackled many different ways over the past 50 years, all with little effect, changes in legislation now mean that the "Repeater Keeper" (the licensee of the station) is responsible for anything his station re-transmits, and many people have installed remote switch off facilities. It can be endless fun forcing the keeper to switch it off, waiting for it to come back to life again, then forcing it off.

You have to remember that these people have constructed, paid for and installed this equipment for the sole purpose of retransmitting what is on one frequency, on another, usually at much greater power and over a vastly wider area, and now they are also responsible for that signal. In the past, people have been prosecuted for repeater abuse, and the evidence given has been nothing but the retransmitted signal - the change in the legislation means that whatever the repeater retransmits is the direct responsibility of the repeater keeper, and any so-called abuse must be traced back to the source rather than just using the repeater output as evidence.

R.I.D. Repeater Improvement Devices

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.

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.

These radios are ideal, high power output, low current consumption, plus you can change the frequency without the hassle we used to have in finding crystals. They are small enough to fit inside small die cast boxes, and if left in their case, RF proof insofar as the transmitted power does not seem to infiltrate the audio source. You can knock up a really good device for well under 100, deploy it, and retrieve when the battery is flat minimising the chances of being caught to almost zero! Search eBay to find some bargains.

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.

Antenna Length

For 2 Mtrs., a 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

Laughing modules from a greeting card

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! Now fully documented
HERE

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 held "open" by the lower power bug, it then timed out if the other party didn't talk over it.

You have to think about it, as it is not readily obvious what this 'easy to make' device can do, if you are on the repeater committee it looks like a serious fault that has to be rectified, to the casual listener it's not obvious. However, this has the effect of targeting the very group of hard-core nutters that matter, the demented repeater keeper and his cronies, it'll have them pulling their hair out - if they have any left.

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 commercially available crystal controlled transmitter modules.

All you need is 48.5Cms of thin wire for an antenna, and off you go.

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!

2011 - Components for a RID (Repeater Improvement Device)

A quick look around the Internet has brought up good sources of parts to make your own Repeater Bug.

You can't beat a second-hand handheld as the transmitter, reliable, re-tuneable, usually with a tone-burst included and small. Check Ebay.

Digital Recording Module, sound source, just the job and very cheap  HERE

Quartz Clock Movements:-

http://www.cousinsuk.com/catalog/8/1171/1405.aspx

We can't find any identical quartz movements at the moment, the ones the LPWS used were standard quartz clock movements with a pair of contacts that momentarily made contact "on the hour" and triggered an external chiming device.

This is one of the chiming quartz clock movements, the 2 wires "make" momentarily every hour to provide the trigger for the timer. OK not high tech, but experience shows that electronic timers don't like being in close proximity (inside the same box!) to local RF sources.

Advantages:- It works, the battery lasts >6 months, cheap, accurate - so you know when in the hour the device will be triggered, small.

Audio Source/Digital Sound Module 2012

Many thanks to G6JNS for emailing this marvellous device! It works, it's cheap, and it's small.

With 20 seconds recording time it is the ideal sound source for a Repeater Improvement Device, 20 seconds might not sound much, but it is just about perfect.
The output is OK to use straight across the microphone input of most handheld transceivers or you can retain the speaker for simple construction.
The microphone for recording your sounds or message is on the right, the other 2 components are the push to record button, and the push to play button. The latter would be replaced with a trigger from the timer or a simple tiny relay will do.
Designed to run on 6 volts, but seems to work quite well below this voltage.

The best thing about this is the price, 3.59 inc VAT!!

Order from Mindsets Online

 
 
      "Wicked" Willy Bodwen ex Sgt. 3116 (forced to retire & not a laughing policeman!)

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