Sunday, 7 October 2012

PMR446 Parrot Repeater

This summer I visited Ireland on holiday. Part of the fun of going over was to set up a simplex "parrot" repeater on the PMR 446 MHz band in the Galway / Clare area with local radio enthusiast Luke 29ER139.

The principle of the simplex repeater is that it receives a transmission, digitally records it and then automatically retransmits that recorded message. Hence it's commonly described term: the parrot repeater. The useful thing about the simplex repeater is that it can be connected to most transceivers on a single frequency. No need for a duplex (dual frequency) facility. By recording and repeating a transmitted message with a repeater station set up on high ground, communication range can be extended. The only problem with this system is that you have to wait for the retransmission to finish to be able to reply. There is a time limit with the parrot, usually no longer than 30 seconds.

The following YouTube video shows now a simplex repeater works.


Very popular this days are the Pan-European licence-exempt PMR446 walkie talkies. Being low power devices the range is small, several 100 metres in built up areas to several kms in clear countryside. Having a simplex repeater allows these walkie talkies range to be extended over a greater area. Luke and I decided this was the best cost effective repeater system for his local area.

A Radio-Tone simplex repeater controller (SRC) was purchased online from eBay and sent over from Hongkong and taken over to Ireland. Luke supplied a Puxing 777 handheld 5 watt UHF transceiver and is easy to set up with the SRC. A lead acid 12 volt battery was chosen to power the repeater with a trickle charger off the mains electricity. The SRC has an internal rechargeable battery and that was removed, as the the unit can run on 12 volts. Unfortunately the manufacturers of the 777 doesn't recommend voltages higher than 8 volts as it uses a 7.2 volt battery pack. So I had to make a 7.2 volt regulator using kitchen table technology. Going through Luke's components and scrape pile of old radios, I managed to build a L200C regulator circuit. This was all mounted in a plastic tub ready for action. For an aerial system we decided upon a Nagoya NL770 mobile antenna, as it's a 5/8wave over 5/8wave colinear with some dB gain, light weight, and has a low SWR on 446 MHz.

Testing the repeater on a dummy load. To the left is the regulator,
right is the 777 and at the bottom is the SRC.
The homebrew L200 regulator circuit built inside a CB pre-amp box

The next day we drove to a nearby high spot which is about 900 feet asl to install the repeater in a shed (with permission of course). We fixed the antenna on a plastic drainpipe and mounted it on top of the shed. Connected several metres of mini RG8 coax cable between the repeater and antenna, and did the final checks. All was working fine.

Luke installing the antenna

Overall the repeater has a good and reliable 20 plus km range, through quite a hilly area with a wide coverage of forestry. We were pleased with the range as UHF signals don't work well in wooded areas. So now the locals on the border areas of county's Clare and Galway a free community repeater on PMR ch 7 no tone (no ctcss at the moment).

I recently spoke on the phone to Luke the "repeater manager", and it's still working. The only problem is that the cheaper type of PMR walkie talkies have poor transmit audio and don't reproduce well when repeated. Next time I'm visiting Ireland, I'll check the audio settings, replace the coax with a higher quality coax as mini RG8 is a bit lossy at UHF, replace the antenna with a higher gain model, and programme the tone squelch if there has been any abuse.

Monday, 4 June 2012

Binky Goes Off-Grid

Binky, an old friend of mine who lives in a nice wooden cabin on a farm, contacted me recently needing help putting together her off-grid alternative energy system. Now for many people having an alternative energy system has become the latest middle class hobby to save the planet (said tongue-in-cheek). But for Binky it's essential as she has no mains electricity. I went down to see her and she presented me with a:

* 6 amp solar panel (from the USA but can't remember the manufacturer)

* a very fancy all singing, all dancing charge controller unit (Schneider C40) to prevent overcharging

* an amazing bank of industrial 70 Amp hour nicad cells that was she purchased secondhand (Alcad LC-70). The nicad battery consists of 10 x 1.2 volt cells linked together to provide 12 volts.

* a small cheapie (but very useful) multimeter to check the voltage of the battery.

My brief was to put it all together in a safe and efficient manner. For a start the voltage of the system is 12 volts, which means thick cabling as there is potentially high currents involved and to avoid power losses. Luckily Binky is quite a low power user. She mainly wishes to power a small DAB** digital radio and a lighting circuit, but with plenty of room for future expansion. Fuses need to be added and a meaty diode in-line with the solar panel to prevent power feeding back down.

"Mains" style switch/fuse boxes was used with 13 amp fuses, between the battery, charge controller and solar panel. Used "cooker" cable to wire it all up. All the connections are through a large "choc" block, which also supports the diode. All of this was bolted onto a wooden panel to be mounted on the wall. At the moment all power distribution is via automotive "cigar lighter" connectors. Not the best connectors in the world, but useful for now.

As the system evolves I will update you all on its progress.

Best wishes from Dave the Pixie

**Digital Audio Broadcasting

Sunday, 6 May 2012

21 to 30 MHz Mobile/Portable Antenna

A few months ago I purchased at a radio rally a Sharman Multicom 40M band mobile antenna on a whim. Wasn't really into using it, so decided to convert it to other bands. Initially it was going to have a frequency range of 24.9 to 29.7 MHz to cover the 12M & 10M amateur bands with 11m CB. It was going to have a base loaded coil with 5 taps to select the bands required. As I was experimenting a quick change of mind occurred and it was decided to add the 15M (21 MHz) amateur band.

The antenna consists of two sections. The bottom half which is a fibre glass tube with the loading coil and at its base has a standard 3/8" UNF thread, and the top half which is a stainless steel whip. Two grub screws hold in the whip and allows adjustment for tuning. As there is plenty of enamelled wire (22swg) in the bottom section, this can be reused to wind loading coils for other frequencies.

First stage of conversion is to carefully cut off the heat shrink plastic off the the lower section. Cut or desolder the enamelled wire from the base. Unwind the wire so it is straight and parallel to the bottom section, down to the base with the 3/8" thread and cut. Put aside the surplus wire for later.

Glue 5 bolts 40mm apart at the bottom of the bottom section, 10mm above the antenna base. These bolts will be used as taps for band selection on the loading coil. Araldite epoxy resin and 5mm diameter brass bolts was used.

On the highest bolt (from the base) connect the wire. This is the 28/29 MHz tap. You can solder or use nuts and washers to make this connection. Whatever method, don't forget to scrape the enamel off the wire otherwise you will have a bad connection!

Between the 28/29 MHz tap and the 27 MHz tap is 3 turns of wire.

Between the 27 MHz and the 26 MHz tap is 3 turns of wire.

Between the 26 MHz tap and the 25 MHz tap is 2 turns of wire.

Between the 25 MHz tap and the 21 MHz tap is 11 turns of wire.

Solder a short wire link from the antenna base and connect to the 21 MHz tap.

I wanted the whip to slide inside the antenna for storage. So the two grub screws on the top of the bottom section was removed to use a 4mm thumbscrew or similar. Unfortunately my local hardware store didn't have a thumbscrew, so I used a 4mm bolt bent into a L shape. I inserted 50mm (2 inches) of the the upper whip and tightened up the L bolt, to allow for future adjustments. Tape or use heat shrink plastic over the wire along the bottom section to the 28 MHz tap.

The antenna was tested on top of my van using a Sirio SO239 body mount with a 3/8" to SO239 adapter. As an experimental antenna, I used thin strips of tape to hold the windings in place. Wire jumper made from 160mm of flex with crimp connectors both ends. Connect one end of the jumper to the 21 MHz tap with a wing nut, and use the other end to connect to select the other taps, with a wing nut. For 21 MHz, remove the jumper wire.

Minor adjustments were made to the windings to improve the SWR. When you are happy with the SWR, glue or use self-amalagamating tape over the windings.

The SWR bandwidth is nice and wide. Measurements taken with a MFJ 269 Antenna Analyser which I recently purchased from Roy at

10M Section
30.0 = 1.5
29.5 = 1.4
29.0 = 1.3
28.5 = 1.3
28.0 = 1.5

CB27 Section
28.0 = 1.3
27.5 = 1.2
27.0 = 1.3
26.5 = 1.5

CB26 Section
26.5 = 1.3
26.0 = 1.2
25.5 = 1.3

12M Section
25.0 = 1.2
24.5 = 1.4

15M Section
21.5 = 1.1
21.0 = 1.1

As you can see, no need for an ATU (antenna matcher)!

Even though my original intention was to use this antenna static mobile, it could be used for portable work, backpacking, balconies etc. You will have to use a suitable groundplane. I would suggest three wires connected together; 3.40 metres for 21 MHz, 2.85 metres for 25MHz and 2.45 metres for 29 MHz. Better mention that I haven't tried this yet and the antenna may need adjusting.

With hindsight, the use of brass bolts wasn't necessary but looks impressive. A neater way of tapping the loading coil for the required band would be using banana plugs and sockets. Especially better for backpacking.

73's from Dave the Pixie, G7OPC.

Sunday, 1 April 2012

Buying Old and New Equipment

For the radio hobbyist buying equipment, there is often a dilemma - do you buy old gear with a good reputation, or new gear untouched out of the box? Old stuff generally is well built, chucky with a feeling of nostalgia, but can be unreliable and difficult to find spare parts. New stuff has a warranty, usually smaller and more compact, and offer an array of facilities that would be science fiction 30 years ago. Unfortunately the downside of modern gear is minimisation causing difficulties in repair, and lead-free solder is unreliable and harder to work with.

One problem if you buy old or new is finding a competent service technician to repair your equipment, which are becoming few and far between is this disposable culture.  Younger people prefer to deal with computers than get involved in radio - many of which don't even know that 2-way radio even exists.

Using the CB/freebanding radio world as an example. Most 10/11 metre modern "export" multimode rigs are just junk. Poor quality control, bad alignment, and a lot of frequency instability for modern standards. If someone is a keen on freebanding, it would be better to buy a HF amateur rig that has been widebanded.

A more sensible approach is to buy equipment that does the job, whether old or new. Flexibility in choice rather than going for the latest bells and whistles. Better to buy gear that can be written off in a few years. If it costs an arm and a leg may be you are beyond your budget. Another approach is to use modern up-to-date gear for every day operating and use the old rigs for that occasional blast of nostalgia. A bit like having a modern hatchback to get to work and back, but in the weekend polishing your 1970's classic car, giving it a good rev up and a spin down the motorway.

 Good examples for secondhand purchase:

* Big old meaty 20 to 30 amp linear regulated power supplies
* Old 2m/70cm rigs that don't have CTCSS (buy a generic ctcss encoder board to upgrade them)
* Old skool Uniden SSB CB radios (if you have a good "rig doctor" to maintain them)
* Antennas that haven't had much use

One thing that should always be purchased new is coaxial cable. Water slowly enters and corrodes down through the cable.

The following video is a tongue and cheek reflection of the combination of old and new stuff:

 73's from Dave the Pixie

Tuesday, 27 March 2012

Confessions of a Radio Pixie part 2 - Mr. Mervyn: The Spy from the DTI

Mr. Mervyn wasn't actually a spy, he was a radio investigation officer from the Department of Trade & Industry's Radiocommunications Agency, which is now part of OFCOM*. Affectionately known by his first name Graham by radio users locally, he doned in those days a fetching moustache and had a piecing stare through his tinted bifocal spec's. He had busted a few people in his time for using unlicenced equipment, and my time was coming.

Around 1991 I rented a small room (more like a cupboard) off a CB radio shop to do repairs, and one afternoon Graham came in to have a nosey around. He pulled his ID card out and asked to inspect my workshop. Unfortunately I had several shelves of  CB radios that were unlicensable stacked high belonging to customers. So calmly (even though inside I was shitting myself) and said the words, "You can't come in without a search warrant", just miraculously popped out of my mouth. He grinned nervously and replied, "Fair enough". So he hanged around the shop for a while and then left. In the shop at the time was John the sales assistant (who also does repairs) and a regular customer Dave. We bundled all the illegal CB rigs into Dave's car, a Fiat Panda, and drove back to my flat several miles away to drop them off for temporary storage. You would of thought we were dealing in moonshine or even drugs, than radio equipment that didn't have the right stamp on it.

I didn't get bothered again by Graham. Prehaps he had bigger fish to fry, or prehaps I stood up for my rights. Most people would of caved in and let an authority figure in, whether they had the right or not. It's the same with the TV licence. People just let them in, as they think the authorities have some magic device that can detect TV's in the house. Even if it was stored unplugged in the cupboard, lol. This of course is nonsense, and this digression has lead me to an interesting future blog to write my opinions of the TV licence. Watch this space!

73's from Dave the Pixie

* The UK regulatory authority for communications

Sunday, 18 March 2012

Radio Sport - CQ Contest

I've always consider myself a easy going person. I try my best to accept other people's interests and one of my favourite sayings is "nature thrives on diversity". But there is a peculiar aspect of Amateur (Ham) radio which does my head in at times - CONTESTS! Also known as Radio Sport, contests is basically how many stations can you contact within a given period, and with the highest amount of confirmed reports you get a nice certificate.

You may be wondering want's wrong with that? Initially, it's prefectly fine, but on the HF (shortwave) bands it's wall-to-wall contesters almost every weekend. HF has sadly become like shark infested waters. All these contestors do is shout, and shout and more shouting. And all they are shouting about a signal report (which is more or less the same report - 5 & 9), progression number, and a goodbye. Meanwhile other types of operators cannot use the bands. Even as I was typing the draft of this blog, there was a dispute on 80 mtrs where contestors were walking all over M3/M6 foundation licence holders that can't operate more than 10 Watts. Luckily some high powered 400 Watt muscle stations (advanced licensees) came in to help them out.

The following video is from Burt K1OIK who has even more stronger opinions than myself. It's nice to see in the vid that not all contestors are selfish scumbags.

There are of course benefits in contesting. It can hone the skill of an operator, help in understanding radio propagation, fine tune the equipment used, and using frequencies that may be hived off to other radio services. VHF/UHF and microwave contests take considerable skill and patience as long distant contacts are much more rarer than on HF. But on HF many operators seem to suffer from that modern disease of arrogance, ignorance and greed. Walking all over anyone in their way just to get a bit of paper to put in a frame and displayed in their shack.

Is there a solution to this problem? Since amateur radio is well organised on a national and international level, agreements can be made to restrict HF contesting. The radio spectrum is just like the highways: many different vehicles for different purposes but we all have to share the lanes.

73's from Dave G7OPC

Thursday, 15 March 2012

Car stuck on the dunes, PMR to the rescue!

In 2008 I went to visit friends in the west of Ireland. We decided to camp out one weekend in the Connemara. We stayed near Balliconneely near Clifden, which for some reason I kept calling it Ballybikini. We all had a good laugh over my mispronounciation and turned into some good craic. We camped out by the coast on the sand dunes, and was occasionally spied on by a herd of cows and the local rednecks. One afternoon I went off by myself for a walk with a small bag which included a small PMR446* walkie talkie.

Later that afternoon I noticed a very frustated family of city folk from Dublin with their car stuck on small hump on the sand dunes. I went over to investigate, and yes there were truly stuck - the wheels were spinning! There was no way they were getting out the car out without additional help. So I called back to the base camp on the walkie talkie, spoke to Mary and explained the situation. After a while we assembled the task force of Robin, Dave, Cormac and Kevin (apologies if I left anyone out) with rope, planks, shovels and a vehicle. Gradually we moved the car allowing the poor family to drive home. Their grandmother was so grateful for our help that she gave me 50 euros, and told me to buy a drink for myself and all of the lads. Which I dutifully did at the local shop - wine, beer and food for all.

So even those "bubble wrap" walkie talkies often seen in supermarkets are useful radio communication devices and can help in many situations. Don't underestimate them!

73's from Dave the Pixie

* Private Mobile Radio on 446 MHz. A Pan-European system of low powered portable 2-way radios.

Tuesday, 13 March 2012

Confessions of a Radio Pixie part 1 - Jamming

Occasionally I will be publishing articles associated with my dealings with radio in the past including when I was a "rig doctor". For several years of my life I used to repair and service radio equipment especially CB's. I used to have a CB customer called Henry (not his real name) how had a passionate dislike for a breaker that used UK CB Ch31 called Clive (not his real name). Henry wanted to wind up Clive and asked me if I could come out with a "jamming" device. Since cheap CB walkie talkies that were very common in the 80's often had crystals for Ch30, I decided to build a jammer with this crystal. I soldered the crystal into a very small oscillator board powered by a 9 volt PP3 battery. This was installed inside a cigarette packet with a short piece of wire to send out a small scale signal and was hidden up a tree by Henry very near Clive's antenna.

So you may be wonder how this worked? Very simply the crystal oscillator board was retuned from 27.89125 to 27.90025 MHz. Channel 31 is on 27.90125 MHz. So when ever someone was speaking to Clive on Ch31, the different between the two frequencies would produce an 1 kHz audio whistle (middle of human hearing spectrum) on Clive's receive. (As 27.90125 minus 27.90025 = .001 MHz = 1 kHz.) This is known technically as the Heterodyne Principle. But in reality no CB transmitter is never bang on frequency so the whistle will vary in pitch, depending on who was talking to Clive.

Well the feedback I got was that this was driving Clive bonkers. He had this mysterious interference that no one else could hear (due to the fact that the jammer was very low powered). He even got the local electricity provider (known then as SWEB) out to check the "lines" for interference. Luckily for Clive the battery went flat after a few weeks, and the interference "magically" disappeared ;-)

73's from Dave the Pixie

Monday, 12 March 2012

Contacting Wales on Flea Power

Yesterday fellow radio enthusiast Martin M6YFT and I went hill topping on St.Agnes Beacon. It was slightly cold and mist was hanging around us. Visibility was poor, which was a shame as on a good day you can easily see the North Cornish coastline from St.Ives to Trevose Head. The Beacon is the highest point in our area being just over 600 ft asl.

Equiped with a Uniden 2830, Yaesu FT817, Kenwood TH-F7e, Thunderpole mk5 11/10m antenna, and a "pixie" made 2 element yagi 2m beam. The beam was made with bits and pieces: a boom from a TV antenna, elements are structs from a portable massage couch, and a connection box from a CB "wotpole" antenna.

Managed to make a few contacts on the 27MHz CB and 145MHz (2m) amateur bands, but the best was talking to Phil GW0IRT portable in Abergevelly on 433MHz (70cm) amateur band with 50mW and a bulk standard rubber duck antenna. We calculated that it was 143 mile trip. It was a lift condition and soon afterwards signal strength dropped. Must mention that Phil was using a 9 element yagi, so part of this contact was due to his set up.

It was only 2 weeks ago I was having a conversation with a local radio ham where he was saying that life was too short for QRP (low power). But Martin and myself were over the moon in making a contact on what can be only described as "flea power". QRO (high power) is all great and dandy, but working QRP has it challanges, taking patience, and a having a sense of propagation (radio and atmospheric conditions). Getting the antenna system right is always a bonus, as you cannot afford losses at lower power levels. Regardless though of the type of equipment and the power levels used, you can only make contacts when conditions are right.

73s from Dave G7OPC