REPEATERS

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 some of the "repeater groups" think.

Basically, this is a 'Vanity' device, rather like a personalised number plate on a car, it is a way to pretentiously try and elevate oneself above the rank and file radio amateurs by constructing a repeater and ostentatiously believing it is yours and gracefully, or in some cases belligerently, letting others use it.

What happens is that the equipment is set up to receive transmissions on one frequency and retransmit them, usually from a more advantageous position, on another different frequency, whether the originating station wants it done or not.

A license from OFCOM is required. There are several downsides to repeaters, the license holder becomes responsible for the re-transmitted signal. This is of little consequence now as since December 1st 2008 the rules dramatically changed, but in the past, music and swearing etc. were considered illegal.

What usually 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 supply of mains power, and these days, an Internet connection, to run it.

A repeater is a fully 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, a few 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. A CTCSS tone is sub-audible and generated by your transmitting radio, each repeater uses a different tone for activation.

The following illustration should give an idea as to the basic idea of repeater operation :-

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 automatic devices and just simple mucking about and playing music. On a 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 (the repeater) 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 making them switch it off again.

R.I.D. Repeater Improvement Devices

Many new Chinese walkie talkies or handhelds can be found on eBay for as low as £10.00, Baofeng being the most common, these are an ideal basis for an automatic Repeater Improvement Device as they incorporate the battery, VOX activated transmit, and built in CTCSS tone generator.

With a little ingenuity a simple device can easily be made to send the audio through the jack input, set to VOX and automatically transmit as long as the audio is present.

Another recent advantage is the cost and easily found supply of Power Packs or mobile phone chargers, which can power the device for long periods, and are easy to recharge from any USB supply. A much cheaper option than higher capacity genuine batteries.

Antenna Length

For 2 Metre repeaters a simple ¼ wave wire antenna is usually more than adequate. This needs to be 48.5 Cms long or 19.2 inches.

The easiest way is to just strip and cut back the screening on a length of coax, this will actually work far better than the rubber antenna that is supplied with the radio.

Experimentation with antennae can show remarkable effects, we had a very successful remote mounted device that used a wire with a crocodile clip, this was clipped to the top wire on a barbed wire fence, and had the strange property of transmitting  for miles whilst being very difficult to locate as the signal seemed to come from a wide area, in fact the whole field. This had the odd side effect of appearing the be intermittent as when it was raining or damp, the transmitted signal was almost non existent. This was a lucky advantage as the last thing you need is for your handiwork to be found and stolen by your fellow hobbyists.

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 directly to the microphone input. 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, they need a low powered trickle charger.

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 alloy boxes on eBay. 

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 externally by 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 handhelds, 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 brings 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 on 70Cms, 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 and sandals brigade!

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 then held "open" by the lower power bug, it would eventually 'time out' as repeaters usually have a maximum transmit duration built in.

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 has occurred 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 transmit 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.

With the advent of cheap Chinese handheld radios such as Boafeng etc. devices can be made far easier and much more economically than before. At the time, £50 for the circuit and a suitable crystal was considered cheap, now complete dual band radios with a battery are on eBay for less than £20.00!

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The crystal controlled transmitters shown below date from the last century and we'll leave the pictures here as a matter of record.

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!

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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 details of 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.