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Construction Projects

Since this page was first published there has been something of a revolution in transmitter prices thanks to the Chinese.
For a mere £20 or so you can buy a Boafeng transceiver which has CTCSS tones to activate the latest repeaters. These radios also have a very easy interface with external devices such as timers and audio sources, via the jack on the side, there is also power available.

It is dead easy to rig up a repeater jammer/bug/improvement device now, you also have a power source for the timer available. For our prototype, (which we think is the first device of this nature with CTCSS), we used the lead from a speaker/mike and the work took less than 20 minutes to complete using a sound module from a greeting card as the audio source directly wired to the mic input. 100% success!

Above is what you get in the box, they even include the plug and lead, so just cut off the remote PTT and earphone! It's all too easy and too cheap these days, you lucky people! Just search eBay for Baofeng, although the same radios are available under other just as dubious, names.

Project "X"

A prototype "Project X" device has already been made and it is extremely useful, a few modifications are needed before our modular device can be deployed properly, but the performance of the Mk1 is very encouraging.

Project X was a suggestion from an unlikely source at our 2014 AGM, something none of us was aware existed was handed over by a member, a GSM remote switch!

Basically, it is the main core of a cell phone with a SIM card carrier and a relay, it is supplied with a free SIM card, just put it in and switch it on. A call activates a relay and your remote control switch turns on your device, you can even program it for time intervals etc. a very useful gadget, again from eBay.

Use this in conjunction with the Boafeng, and you have a self contained, small, easily deployed device that has lasted at least 5 days in field tests. A doubling of the useful time between charges can be as simple as adding a light sensor so the GSM is only powered in either daylight or darkness. Again, as everything else today, eBay has many ready made devices for sale.

Modular construction simplifies the job, please DON'T try saving space by dismantling the Boafeng radio, just take our word for it!

It is fair to say that several similar projects can be made from old cell phones, but we got this GSM controller donated, however a quick search of eBay UK shows similar devices from £29.95, but be sure to get a 12v one as some are sold for home automation and are mains powered.

Our prototype can be activated by anyone with the SIM card number calling it, it doesn't answer, but the relay activates upon a call. It also has the ability to respond to only one calling number or up to 10.

If only such things were available in the "good old days", what fun!

Sorry we can't make public the size, shape, and colour of the finished article as it would make it too easy to find, but the whole thing is marginally larger than the radio and in a waterproof/rainproof housing.

Only a little more work is required to refine the design, possibly with the addition of a separate battery for the GSM controller as it has to be on all the time to work.

It was suggested at the AGM to book into a hotel and install one in the room, but there is too much of a paper trail to do that without being traced, but what an excellent idea, rather like the "bug" an LPWS member left powered by his bathroom light when he moved house, nearly 5 years passed before it stopped working or was eventually located - and it was a mere 200 yards from The Birmingham HQ of The Radio Investigation Service and the exact same building OFCOM now use for their Spectrum Engineering Officers.

Below is a compilation of old pages, how things have changed!


Build a Repeater Bug/Repeater Jammer!

Build your own repeater bug, or repeater jammer, with our help and advice!

Find your target repeater with the Grid Reference HERE

You can target your own local repeater, or make a device with variable frequencies that you can use on your travels, now that prices of hand held transceivers are falling, especially second hand ones.

Not a great deal of practical knowledge of electronics is required to construct a device, but you will need the basic skills of soldering and drilling etc. Don't be too ambitious at first though, our advice is to keep it simple.

We have made 2 distinct types of device, the simple ones, such as "Tony Toneburst", and the more advanced ones with music, messages, and digital speech.

Equipment / Transmitters


The Wood & Douglas 144FM2T3 transmitter board. As you can see, it is quite small, but compared with some of today's transmitter boards with surface mounted components, it is huge!

This is the Ramsey Electronics FM6, it is TINY and ours transmits 30 miles and accesses a repeater on a ¼ wave length of wire just as shown! The picture shows the top of the board, the components are surface mounted beneath. Shown in this picture are the battery (top), a standard crystal (centre) and a microphone (bottom left). A good feature is that this transmitter works with a mere 6 Volts.


Here is another variation of the FM6, this one was produced by Xandi Electronics in the States, but sadly they have gone out of business leaving us with only 3 of these wonderful transmitters. As you can see, this one is crystalled for 145.025MHz, and has given sterling service in the past. We had to remove it from a device to take this picture.

This is the smallest crystal controlled transmitter we have found, and by far the best. This one worked well in tests, although its use has been limited to a radio rally "talk in" frequency. Fitted inside a packet of 20 cigarettes with a laughing module and 4 AA batteries, it was carried around inside a radio rally by an unsuspecting person while we monitored the effect from outside. It is rock solid on frequency, and powerful for its size. For the test we used a loosely coiled ¼ wave wire inside the cigarette pack. It completely obliterated all signals due to its close proximity. This picture shows it before the crystal was changed, and the microphone replaced with a sound module.

To convert any of these type of crystal controlled transmitters for repeater bug use, the crystal needs to be replaced. New crystals are available from :-

QuartsLab Marketing Ltd.
PO Box 19
Phone  01322 330830
Fax      01322 334904

To work out the frequency required, a little simple maths is required. Assuming you know the frequency the unit is currently set to transmit on, (if you don't, a scanner will give an approximation) and divide INTO this figure the currently fitted crystal frequency. This will give you the MULTIPLIER, quite often 12.
For example, if the transmitter is set for 169MHz at present and the crystal has 14.08333 stamped on it, then the multiplier is 12. (14.0833 X 12 = 168.9996, the Tx frequency)
For Example:- To convert it to transmit on 145.025, the input frequency of a repeater on 145.625Mhz, divide 145.025 by 12 to get the crystal frequency, order a crystal on 12.0854. It's that simple. To ensure the correct type of crystal is supplied, we suggest unsoldering, and sending the old one with the order, that's what we always do.

For some very good transmitter kits and other interesting things:-
Ramsey Electronics

Their FHT1 "foxhunt" transmitter, for US$89.95 had definite possibilities and it is microprocessor controlled with variable time delays etc. It represented excellent value and should have done the job well with only minimal modifications. Sadly no longer available from the manufacturers, although you may find one if you search.


Download our simple resistor colour code program  Resistor Colour Codes

555 Timer Circuits

All these circuits use the versatile 555 timer        

Any Repeater Improvement Device needs to be triggered by a timer. There are a few suggestions .

Our first really successful device, Tony Tone-burst (named by the repeater users, not us), it consisted of a battery, a transmitter, a 1750KHz tone burst board and 2 simple 555 timers.

Why 2 timers? You need 2 specific timing intervals, one for the interval between transmissions, and one for the interval of transmission, later, greater experience gained from making these devices reduced the component count considerably.

Tony Tone-burst sent out a 500 millisecond burst of tone every 28 seconds, this would open the repeater, and just as it was about to time-out, and it was sending it’s Morse ID, the device would send another tone burst and reset the repeater’s time out timer.

This was made before we came across the circuit for our own tone-burst that has a built-in duration timer, if a similar device is made now, only the one timer is needed, the one to set the tone-burst interval, as the duration of the tone is pre-set to 500ms.

Actually, it did nothing to jam or prevent use of the repeater, but as radio amateurs are not fully paid up in the brain department, they would not use it or speak to anyone! In fact several people genuinely believed it was manually operated and that someone was actually sitting and pressing their tone-burst button every 35 seconds or so, and we were accused of paying someone to do it. As they say, the pictures are better on radio!

Later modifications to Tony Tone-burst were a small “laughing module” from a greeting card, and an increase in the transmit time to 1 second. This gave the following effect, tone bust > repeater opens > brief trademark laugh > silence………..timeout  starts > repeater Morse ID > tone burst again > and so on.

For a more standard device we have found that a transmit period of no more than 30 seconds provided the required amount of annoyance without transmitting long enough to be tracked down.

A maximum of 3 transmissions per hour will keep them guessing as to the location, but we suggest only 2 per hour. A simple way to achieve this is to use a small quartz clock mechanism, these are only a few pounds and there are many ways to trigger the transmit timer with one.

A really simple way to trigger the device is to find the works from a chiming quartz clock, these have two wires coming from them that are attached to a pair of contacts that "make" once per hour, throw away the hands and use these wires to trigger the transmit timer.

Don't be too over enthusiastic with transmit periods and the number of transmissions, many of our newer constructors have suffered the loss of expensive equipment this way as the "sensible" radio hams will DF the unit and steal it given half a chance!

A really good ruse is to construct two identical devices and have them set to trigger alternately from different locations, prolonged use of this example showed that they just confused anyone trying to locate them.

The following two simple timers can be constructed without a pcb if required, just solder the components onto the chip, this saves space in a confined area. Both designs are tried and tested and based on the common 555 timer chip, where power consumption is a factor, substitute the standard 555 timer with the µ555 version, but take care as these are very delicate with regard to static electricity.

We hope the circuits are self explanatory! All resistors are ¼ Watt, take care with polarity, the "idiot" diode can be omitted if you want.

Timer One

This timer is the standard design used by us for over many years, the original is still working! It provides the power for your device via the normally open contacts of a sub miniature relay, test have shown that reed switches, although drawing less current, are not nearly so reliable in service. The input "pulse" wanted is a momentary make contact, this starts the timer cycle. Various things can be used for this, but bear in mind that some devices, although they work well in test conditions, do not function when in the close proximity of a transmitter.
Our most successful devices have used one or more chiming quartz clock mechanisms. These are available for a few Pounds, and have a pair of wires that make momentary contact once per hour. Throw the hands away and just use the bare mechanism or 2 for twice an hour operation. Crude we admit, but in the field they work better and more reliably than other designs of more technical merit!

VR1 should be around 1MΩ - 2MΩ to give an on time of around 20 - 30 seconds only, this may not seem a lot, but take our advice, any longer and they will almost be able to DF the unit and steal it! You may need to experiment with the value to get your required "on" time.

Timer 2

This is from the very first successful device made by the LPWS, and nicknamed "Tony Tone Burst". This device utilised the repeater's characteristics to keep it open as the close-down Morse ID was being given. On the face of it, nothing much really, but radio amateurs being what they are, find this monumentally annoying, this stops them from using it as effectively as a 100 Watt carrier, take our word for it. This timer needs to be coupled to a transmitter with a automatic tone burst and the timer pulse adjusted to coincide with the repeater's closedown, usually around 30 seconds of non activity. The tone burst then resets the repeater timer and the cycle repeats. We know it sounds too simple to be effective, but remember we are dealing with simple souls, IT REALLY DOES WORK!

The blue resistor is the timing period controller and the one to change to suit your target repeater, ours has a hard wired resistor, but obviously a variable resistor can be substituted.


Diode D1 in both circuits, as well as the "idiot" diode are standard diodes you find lying around, if you want a part number, try using 1N914, 1N4148, or similar

Theoretically, the 555 can supply the current for a low power device without a relay, but remember we are dealing with RF in close proximity, and in practice this does not work as the timer needs to be insulated from RF feedback. Consequently, a relay must be used.

The idiot diode is there merely to prevent damage from reverse polarity, not a bad idea if you are making a sealed package, it will protect your circuit during use and testing and any accidental reverse polarity when changing the battery pack.

Testing can be done easily with a simple led and resistor such as this:-

We suggest the complete and tested circuit is fitted with wire "tails" for connection and sealed with self amalgamating rubber tape, or silicone sealant, to prevent the ingress of moisture etc.

Here is a block diagram of the component parts of a Repeater Bug, for ease of construction we always power the sound source and clock timer separately from 1.5 volt cells soldered in place, in practice these batteries last in excess of 12 months.

From the relay in the timer module, one "hot" wire is required to power both the tone burst and the transmitter, if a more complex audio source is used, extend the wire to activate this as well.

In the old days we had to use an auto-reverse Walkman unit with a C60 cassette in it, until the tape broke! Luckily, now we have innumerable sources of digital sound recorders and audio modules available for a few pounds, like the birthday card laughing module that is ideal.


1750 KHz Toneburst


Due to the introduction of CTCSS sub audible tones, the following information is somewhat obsolete, it will remain here for historical accuracy. To open the vast majority of repeaters in the UK, you now need a continuous tone on your transmitted audio, that is supposed to be below the range of human hearing.

Full details of CTCSS tones along with ways of modifying existing equipment can be found on our CTCSS TONES Page

To access most repeaters in the UK, a 500 millisecond 1750 KHz tone burst is required. When the repeater hears the tone, it switches on the transmitter and re-broadcasts anything heard on the input frequency. Most repeaters using CTCSS still retain the ability to be activated by the old style tone.

There are numerous commercially made tone burst modules available for the modification of ex PMR equipment.

The Wood & Douglas TB2 tone module, shown here, can be easily made yourself with readily available components.

The adjustments are for output level, set at quite a low volume for best results, and the of the tone burst frequency. One advantage of this module is that it actually times the length of the burst to 500mS itself. This means that it can be wired across the input and when power is applied, it self times the tone burst, quite useful!


If you are a clever sod, like some of us, you can make your own tone-burst module with the LPWS design below.


This is a simple, cheap, and effective 1750KHz toneburst circuit, essential for "opening" older repeaters in the UK.

This circuit has the added advantage that it can be left powered as it has an inbuilt 500 mS tone-burst timer. [i.e. when power is applied, the tone-burst only sounds for 500mS, after than a mere few µAmps are needed on standby]. If you are using a common ground (0V) you may be able to use just the output to the "hot" side of the TX input, check for polarity, otherwise it can be wired permanently across the input in parallel with your audio source.

The IC is a Motorola MCI 4001BCP or equivalent.

The only important adjustment is RV1, this controls the output frequency. There are several ways to adjust this, but assuming you don't have a frequency counter, you can use trial and error by testing it on your target repeater. Start with the trimmer in the centre position, most repeaters are very tolerant! [unlike the repeater groups!]
Another tried and tested way to set up the tone is by ear. Use a hand-held or a known good radio, and monitor it on a scanner, with your tone-burst connected to your transmitter apply the power and adjust for the same tone. RV2 adjusts the output level, in general, we have found the lower the level - the better it works.

If you want to get a constant output from the LPWS tone-burst circuit for testing etc. simply apply 12 volts via a 100K resistor to pin 6. This will disable the internal timer. 

This can be built on a board, or to save space, we have one actually built entirely on the back of the MCI 4001BCP chip. Another space saving way, is to use an IC socket, solder the components to the pins before plugging the chip in. After testing, both RV1 & RV2 can be substituted for fixed resistors to save space.

Tried, tested & it works! (well ours do anyway)


Here is a website for the hobbyists, like the majority of LPWS members, there are interesting projects and loads of modifications for existing kits. OK, not all radio related, but some interesting things just the same. Look in the TECHNOLOGY section.

Found on Instructables, we have just made one of these TV-B-Gone devices a mere US$19.95 kit.

Great fun when such places as Comet and Currys, also in department stores, be careful in pubs though if there are any morons watching football! Plunges John Lewis and Selfridges into silence!

A good 25 metre range, sometimes up to 50 metres. The small EPROM contains a list of "off" codes for nearly all brands of TV, pressing the button starts it scrolling through the list with Samsung, Panasonic, Sony & LG coming at the beginning. Another press starts the sequence again, the whole list takes about a minute to finish.

(A side effect of this device is that it will turn on any set that is already off though.)

2 long range IR diodes and 2 wide dispersal diodes, can be modified to take a matrix of 24!

A good source of circuits for hobbyists can be found HERE

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

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