Saturday, May 6, 2017

Installing the 70cms Repeater at Knockroe

A meeting prior to the installation ensured that all parts had been purchase and also who currently had them in their posession.The last item required was the 20ft pole. John looked after the purchase and delivery of the pole to the site.

Gerry took charge of the guying equipment and all of the necessary parts werre handed to him. Andrew, took charge of the fencing materials and the parts for the fourth guy which needed to be set in the ground on the day.

Steve held the repeater and sundry items and spares should they be required.

The group met in Abbeyknockmoy and headed for the site. Marlow joined us and oversaw the operation on his site.

The first task was to work on the brackets to hold the pole against the wall of the hut. Gerry took charge of this with the assistance of Arek.  

The next task was to organise the staying point for the fourth guy. Joe and Andrew looked after this duty. A fair bit of digging was involved until a huge lump of rock was found. 

This rock was going nowhere so the best course of action was to drill into the rock and insert a rawl bolt. This has a couple of small clamps added and the fourth guy was affixed to this. Concrete and rocks were poured over this and then the rest of the earth covered it. A small fence was built around this area to prevent cattle damaging the guy and staying point.

The pole was raised to ascertain the length of the steel guys and also the fourth guy which would have been longer once this was done it was time to bolt the antennas to the pole. 

The raising of the mast was not too difficult with a little muscle and weight behind the mast

Gerry spent much of the time on the roof of the hut ensureing that the guys were secure. The tensioners did not need adjustment so there will be plenty of play to tighten them in the event of the guys stretching.

And so the last of the guys was attached and secured to the Rawl Bolt on the rock. With all in place it was time to look upward and see the results of the work done.

And then into the hut where John had been working on installation of the Repeater and the APRS Digipeater.

A great day was enjoyed by all. The installation took four hours to complete. A great days work was done by all with special thanks to the Team - John EI1EM. Tom EI2GP, Joe EI3IX, Steve EI5DD, Andrew EI3FEB, Gerry EI8DRB, and Arek EI9GWB and not forgetting Martin List-Petersen who oversaw the operation and took the photographs shown here.

Galway 70cm Repeater - EI7AKR

The Galway VHF Group 70 cms Repeater is now located at its permanent home on Knockroe, Abbeknockmoy, Co. Galway. This is a prime site with a superb and unimpeded view in all directions. Initial predictions using Radio-Mobile show a pretty uniform coverage of the County of Galway in almost all directions. 

As can be seen below, the coverage is impressive and will certainly be an improvement on the coverage of the present 2 metre Repeater located on Tonabrucky just outside of Galway City. This will facilitate many operators who just can not experiment with communication over distance using UHF Radio. The primary objective is to give saturation coverage of the County and, more importantly, the main routes into and out of Galway City. Regrettably, this is not possible in the direction of Clifden due to the proximity of the 12 Pins and Maamturks, however, coverage into Oughterard, and just beyond, is possible. Whilst predicted coverage is impressive, the actual mobile coverage may bring in even more surprises.

The Individual components of the Repeater are as follows

 The Repeater is fabricated from a modified Commercial Kyodo UHF Repeater unit running 40 Watts fed into a 4 stacked dipole array with an actual gain of 6dB. Naturally, ultra low loss coax feeeder will be used. The Repeater was supplied by WESCOM and modified by Enda O'Brien EI5GMB.

To achieve the isolation between transmit and receive it is necessary to insert a band pass/band reject filter in line. This is one area where compromise is not an option. A set of six Sinclair cavitiy filters were purchased. Expensive but perfect for the job. Careful tuning using a spectrum analyser and/or a VNA was required to achive the best possible rejection. The specification suggested that there would be 120dB of isolation betwwen the recive and transmit frequency and we were using a 7.6MHz split.

Ideally the cavity filter needs to be tuned into the feeder and antenna in use on site. Although the cavity filter can be tuned into a 50 Ohm load, it will be necessary to tweak it up on site. If one changes the antenna or feeder the whole process of tuning the cavity filters has to be repeated as minor changes to the load will alter the characteristic curves.Shown below are the characteristic curves on the receive tuned to 432.825MHz. 

We were fortunate that we were able to tune the cavity filters into the correct heliax feeder and antenna system prior to installation on the permanent site. This will reduce the amount of time spent tuning on site. It will probably be necessary to make minor adjustements before leaving the repeater once installation has been completed.

It is now possible to run 30 watts of power without any worry about desense or drift. With the present power setting it has been possible to get into the repeater with an S 1 signal received from it whilst it is tranmitting 30 watts. This may have to be balanced on site but at this stage it may not be necessary. 

There is no noticeable temperature effect causing the cavity pass or reject bands to drift. We had tried the small Procom type filters which actually heated up when our transmit signal was passed through them. This resulted in the characteristic curves to drift and resulted in desense after a couple of minutes of use. A search on the internet revealed the Sinclair cavity filters.These were by no means cheap but it is far better not to compromise the system for the sake of saving a few Euro. 

An RC-100 Repeater controller deals with the identification and timings of the repeater. The repeater is accessed using a CTCSS tone of 77 Hz as it is considered irresponsible to allow spurious triggering from a carrier operated squelch. Through this controller, the Repeater can be switched off at short notice if required to do so. 

The Antenna is the most important part of the set up.

The antenna system was obtained from Radio Structures Ltd in the UK. It was designed specifically for the task taking into account the Transmit and Receive frequencies. the Gain of the antenna is 5.5dB gain over a 1/2 wave dipole.The antenna is true omni-directional and the characteristics are shown below. 

There is little point in producing a professional system without a professional antenna fed with low loss coax. In our case we used Anfrews heliax with negligable losses at UHF.

Status - Active

Callsign EI7AKR

Repeater Access by 77 Hz CTCSS Tone

Modulation Narrow FM (+/- 2.5 KHz)

The IRLP Node Number is 5705
The Echolink Node Number  5705

Echolink Node EI7AKR-R

Locator Reference for site IO53PK
Output Frequency 430.825 MHz  

Input Frequency 438.425MHz

 Frequency Shift + 7.6 MHz 

Please note Time-out 2.45minutes

Repeater Keeper - Steve Wright EI5DD
Reports to

Sunday, March 19, 2017

Experiments with C4FM

We now have six stations in Galway operational on Yaesu Fusion. Steve EI5DD, Tom EI2GP, John EI1EM, Arthur EI7GMB, and Gerry EI8DRB,  have FTM400XDR transceivers and Andrew EI3FEB has a FTM100. Dermot EI7IX from Westport recently purchased an FT100, whilst Joe EI3IX, and John EI7FAB, from Castlebar Co Mayo, should be on shortly so the efforts have finally borne fruit. Arthur EI7GMB,  will have an FTM100 in Galway shortly. Gerry EI8DRB owns a Yaesu FT991 which incorporates C4FM. Nine on the air in a short time is impressive.

The Limerick area, due South of Galway,  have a Yaesu Fusion Repeater which provides a good signal throughout Galway and into Co. Mayo as far west as Westport. The current number of Fusion operators in the Limerick area would appear to be around ten or eleven.

Plans are to place a Wires-X gateway online by the end of April, which will serve Galway City and the surrounding area of 25 Km radius.

The first experiment was carried out between EI3FEB in Headford and myself in Galway City - a path of 23.5 Km but it had a few hills in between the two stations so was a poor path at the best of times. The path was chosen as this was probably the worst signal strength achievable.

Both rigs were set up to transmit 5 watts and the initial transmission was made on FM

As can be seen on the display the signal strength did not even register and the FM signal had the usual hiss encountered with FM signals received on the fringe area. For an S0 signal it was not too band. The FTM 400 recorded the returned signal as S 0.5 - S 1. Readable with plenty of hiss. Note the FM displayed to the right of the frequency displayed indicating this was in the FM mode. The lower green light indicates FM reception.

The mode was changed to C4FM and the signal received was most impressive

This signal was still received at a S 0 level but his time in C4FM. The quality of audio was crystal clear with absolutely no background noise. Note the DN displayed to the right of the frequency displayed denoting in digital mode. The blue light denotes the reception of a digital signal. When the digital signal is received other information is embedded within it which includes the Callsign and also GPS coordinates. The distance as shown was derived from that information.

Check out the YouTube video
Quite impressive with no R2D2 sounds from the received signal.

More to follow   .......................... 
Original work from the EI5DD/G4GFC pages Click here

Wednesday, August 13, 2014

Galway VHF Group APRS EI2GCP

The Galway VHF Group APRS system is to be completely overhauled. The introduction of an I-Gate at the Galway City site in Mervue will feed data directly into the International APRS network enabling tracks to be viewed live on A weather station feeding live information into the network will also be installed at Mervue.

Pictured below, is the setup for the EI2GCP APRS I-Gate to be located at our Galway City site, Mervue. From top to bottom, Tiny2 TNC operating in KISS Mode, underneath,  PC Engines WRAP embedded linux board running aprx iGate software and below this, the Philips PRM 80 VHF PMR radio programmed for 144.800 MHz.

Pictured below, is the Weather station under test at EI3FEB's QTH. Judging by the sky in the background, the weather station will get plenty of abuse as Galway aproaches the winter months. This Weather Station will be transferred to the Mervue site around the 25th of October.

On the 25th of October the APRS and Weather Station was installed at the Galway City Location in Mervue. The existing tranceiver was replaced with a Phillips PRM 80 Commercial PMR set operating on 144.800 MHz. Strangely, the Yeasu FT8900 looked as good as new and was working perfectly despite being left on the roof for almost 5 years. The APRS I-Gate was connected to the Tracker2. The whole system is located in a weatherproof box on the roof. As is obvious, the box has protected the equipment well over 5 years.

The Weather Station was clamped to the mast and oriented in the correct position. The "Bird-Box" contains the pressure and humidity sensors, the two other items are the Anemometer and the Wind Direction indicator. All being secure, power was applied and connection to the internet was initiated.

Initially, information was not showing up on as expected. Settings on the I-Gate were changed by remote access which allowed the Tracker2 to communicate with the system that had previously been set up for a TNC2. Everything sprang into life with the new settings and results can now been seen on in the illustration below.

The Weather Station symbol has been staggered slightly to make it easier to click on the WX symbol. By clicking on the WX symbol an information box will open and show the up to date parameters recorded by the Weather Station. No rain in Galway since the since the Weather Station came on line. This will undoubtedly show some readings in the very near future.

Since the tranceiver was changed, the setup seems more sensitive and is receiving more distant stations. Possibly conditions on 2 metres but maybe due to the different squelch system allowing weaker signals to be received.

Once the second Digipeater is added to the Knockroe site, traffic from further afield will be relayed back to the I-Gate in Mervue. This will extend our coverage considerably and result in coverge overlapping other systems located in the Midlands and to the South-East. This will make it possible to track seamlessly across the country. It remains to be seen just how far the coverage extends once the sytem is completed.

Frequency 144.800 

Callsign EI2GCP

                                                              Location       Mervue
                                                              Locator         IO53LG 
                                                   Co-ordinates  53.285981, -9.031202