Monday, October 17, 2016

Galway VHF Group Journal

Following the success of the pilot issue, the Galway VHF Group Journal will be available around the begining of November once  the layout has been completed. The content of this Journal centres around original articles submitted by VHF Group Members. Articles include News, Reviews, Construction Projects, radio related applications for the Raspberry Pi, current VHF Group Projects such as the APRS, the 4m Gateway, and the Repeater and much much more.

Here is the front page of Issue 2 as a sweetener

This issue contains 32 pages packed with News, Reviews, Technical Articles and Features along with VHF Group activities.

Wednesday, August 13, 2014

Galway VHF Group APRS Network EI2GCP & EI2AKP

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.

A second APRS digipeater will be installed at the Knockroe site, Abbeyknockmoy, Co. Galway. Coverage will be almost as good as that seen for the 70cm Repeater. This will provide seamless coverage and handover to digi-peaters covering the midlands  and possibly further south - something that would not be possible unless the higher site were to be employed.

Any data received by the Knockroe digi-peater will be retransmitted, picked up by the Mervue digi-peater and fed into the International network via the I-gate. This upgrade was long overdue and it will open many possibilities for the Galway VHF Group and AREN operations both in Galway City and County Galway.

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

 Awaiting installation on site

Callsign EI2AKP

Location Knockroe, Abbeyknockmoy
Locator       IO53PK
Co-ordinates:    53.420201, -8.742071

4 Metre ECHO/IRLP Gateway EI4GCG-L

The Galway VHF Group 4 metre Gateway will be located on a high spot in the Mervue area. The 4 metre Gateway is not intended to cover any more than Galway City and surrounding areas. We are happy enough if it just covers the townlands around Galway City such as Oranmore, Headford, Furbo, Moycullen, and Claregalway. Those with good antennae may access this Gateway from further afield.

The predicted coverage from RadioMobile map reveals just perfect coverage for our needs along with some addditional areas. City wide coverage and even coverage to Athenry, Kinvara and beyond Claregalway and further out from Moycullen has been confirmed by the use of the existing APRS coverage on 2 metres from this site.

The 4 metre Gateway was built using a Kyodo commercial Low band Tranceiver. A Raspberry Pi ECHO/IRLP controller was added and the radio is fed into a 4 metre dipole located on the roof of the building. Nothing stunning or startling about this system; it is very simple. Remote control is also included if necessary to switch the Gateway off at short notice.

This is not intended to be a "DX machine" but merely an asset to bring in activity from other EchoLink or IRLP Nodes around the country or abroad. Some VHF Group members are often working elsewhere so this will provide an excellent opportunity to keep in touch locally. There was never really a plan for this to be used from a mobile operation point of view, but it would be possible. One does have to consider that to key in DTMF tones is neither conducive to good driving practice nor within the framework of the new Road Traffic Acts.

The 4 metre Gateway will be located on 70.425 with CTCSS access using 77Hz tones. Carrier access is a recipe for disaster as it is irresponsible to allow spurious opening of the squelch as so often happens. It is possible to chat away on channel without the tones switched on and the unit will not activate. If, however, somebody does access the Gateway, one can switch in the CTCSS tones and have a conversation with the operator concerned. Obviously it is better to monitor this channel without CTCSS tones switched in. This will enable local conversation on the same channel as well.

The Completed Project Prior to Installation

The Echolink/IRLP controller is Raspberry Pi Micro-computer linked to an Echolink/IRLP controller board which handles the audio, decodes the DTMF tones and sends its I/O to the internet and associated servers. The Project is shown below and at the bottom left is the Echolink/IRLP controller board, above this to the top left is the Raspberry Pi Computer, to the top right is the temperature controller which switches in the fan if the P.A. starts to warm with excessive use and to the bottom right is the 12V to 5V converter to power the Raspberry Pi. The larger Ribbon Cable connects the Echolink board to the Rasberry Pi and the smaller Ribbon Cable connects the Audio I/O and PTT and control voltages from the Rig. The small SD card sticking out of the Raspberry Pi contains the software and commands peculiar to this Node.
Here is the front panel with rig and fan sitting on top of the box. these will be mounted on a bit of Plywood for stability before installation: The LEDs just monitor 12V, 5V and the Fan voltage. A small temperature probe fits into one of the fins of the heat-sink on the Rig and, via the controller, switches in the fan if the the temperature of the heat-sink start to warm up. This is only a precaution against those with long overs. 
Below is a picture of the Kodo Tranceiver which has the power turned back to 12 watts although capable of 25 watts normally. There is only one simplex channel programmed into this tranceiver as there will be no need to change channels. The only mods required were to extract Audio from the Receiver to the Echo/IRLP Board, to inject Audio from the Echo/IRLP board, COR sense and PTT line. We chose this tranceiver as its performance and sensitivity are second to none. Note that this is NOT a Repeater but a Simplex Gateway - anyone transmitting into this locally will not be re-transmitted whilst the unit is receiving their signal. The antenna used for this project will be a Vertical Dipole. As can be seen we look after our local communications company!

With both Echolink and IRLP it will be possible to connect to many Repeaters and Gateways around the world from a simplex tranceiver. Many foreign operators use this facility to speak to Amateurs in Co. Galway and surrounding areas. If you are abroad working or on  holiday, this will be the ideal system to keep in touch with home.

Currently off Air for Servicing

Callsign EI4GCG

Node Access by 77Hz CTCSS Tone 
Modulation Narrow FM (+/- 2.5 KHz)

The Echolink Node Number:  5422
The IRLP Node Number:       5422

EchoLink Node Call EI4GCG-L

                                                     Power  -        12 Watts
                                                     Antenna -     Dipole.
                                                     Location -    Mervue, Galway City
                                                     Locator -      IO53LG
                                               Co-ordinates -   53.285981, -9.031202

Operating Frequency 70.425 MHz

Galway VHF Group 70cm Repeater - EI7AKR

The Galway VHF Group 70 cms Repeater is shortly to be 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, along 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 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.

See below photographs of the individual components of the Repeater

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.

The following pictures show the results of tuning the cavity filters under initial test tuning into the 4-stack verical dipole array.

Fig 1 Rx Notch and attenuation


Fig 2 RX Notch on TX Cavity 

 Fig 3 Tx attnuation and SWR

Fig 4 Tx Notch on RX Cavity

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 the full 40 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 40 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.

In addition to the standard Repeater control circuitry, in this case a RC-100 controller, there will be a Raspberry Pi ECHO/IRLP controller. This system will considerably enhance the operation of the Repeater by bringing in activity from other countries and not forgetting other areas around Ireland. See the information about the 4 metre gateway for more information about the EchoLink Controller boards. Remote control is fitted to switch off the Repeater at short notice or in the event of interference. 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.

RC-100 Controller
RPi  ECHO/IRLP Controller

The 4 Stacked Dipole Array -  Pointless using anything less on a UHF Repeater

Polar plots prove the perfect choice for this application

Some views from the Repeater Site

The Hut -- Our 40 ft Mast will go on the near right hand corner

The View Towards Castlebar

Looking in an Easterly Direction

View to South East - Derry Brien

View of Clare Direction

The View of Galway City is clear but we noted that Tonabrucky is obscured by the hill at Ballinfoyle. In keeping with the coverage map, there is obstruction in the direction of Kilrush by the Clare hills and the Limerick direction by the Slieve Aughty mountains. There is a pretty good path into Ennis. It may be surprising where the reflections and refractions may take our signal.

Recent tests gave an S7 from EI9JS using 5 watts (not a million miles from Knock). EI3IX managed an audible but noisy signal with 50mW from a handheld. He was receiving us at S7 in Balla, on high ground, near Castlebar. Arthur, EI7GMB, came in with a good strong signal from Galway City. Even the three Aran Islands should get clear signals on the Easterly facing sides. All very promising!

Please note that the Echolink may only be switched in as or when there is a need to do so. For the time being this is not a priority.


Awaiting Installation on Site

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