Friday, December 31, 2021

Considering 23cm Operation?

The 23cm band is the lowest in the spectrum of microwave bands available to the Amateur Radio operator. With the advent of the new transceivers, it is now possible to make inroads to this band with little difficulty. The power levels of 10 watts are suffient to drive linear amplifiers and more than enough for point-to-point QSOs with reasonable antennas.

The 23cm band is popular for Moon bounce, ATV and Satellite operation and proves an interesting challenge for point-to-point communication.

Unlike the 2m and 70cm bands, it is not enough to put up a vertical colinear and expect miracles on this band. Yagi antennas from 28 element (15.4 dBd gain) to 67 element (19.9 dBd gain) versions are effective and affordable. Because of the short wavelength of the 23cm band, it is possible to produce an antenna with a greater number of elements for and hence a larger gain for a given boom length.

A 23cm Yagi with 70 elements

There are a number of transceivers available with the most recent being the ICOM IC-9700 capable of 2m, 70cm and 23cm. The Kenwood TS2000X was popular and also the ICOM 9100. 

ICOM IC-9700

An alternative to a dedicated transceiver would be a transverter from 28 to 1296Mhz or from 144 to 1296 MHZ.  In many cases it is practical to locate such devices just below the antenna to reduce feeder losses. Transverters are available from SG Labs, Kuhne Electronis and Downeast Microwave. 

SG Labs 23Cm Transverter


DownEast Microwave Transverter with 50W Linear AMP

The Down East Microwave Transverter above is driven by an FT 817 on 28 MHz. Up to 50 Watts output on 1296 MHz

There is no harm in considering a mast-head receive preamp to overcome any signal loss in the coax although it is possible to conduct most portable activities without one.

It is essential that low-loss coax feeder is used for 23cm operation RG 213 is totally out of the question.

Modes of Operation

Obviously SSB, CW and weak signal modes are of major interest as one is seeking DX contacts. Digital Voice Modes will give some stunning results and are worth trying if you are using the ICOM 9700. Experiments were performed with this system using D-Star between two locations with low power on 1296.200MHz and signals just above the noise level. The results were surprising. The signal sounded like a fully queting FM signal coming in at a strength 9.

Propagation on 23cms

It is necessary to have some comprehension of Microwave techniques and the propagation of signals on the 23cm band. 23cms is not confined to line of sight activity and may derive benefit from tropospheric lift conditions due to high pressure weather fronts. During extreme tropospheric ducting, signals may travel further than on VHF. Those living on or near coastal areas may find that some very stable ducts form above the sea alowing considerable distances to be worked. Rapid fading may also be experience in much the same way as experienced on 70 cms.

Tropospheric Ducting

Enhanced conditions will be less frequent on 23cms than on VHF or UHF. The best way to check would be to set the beam towards a known beacon or even a 23cm Repeater where the signal maybe referenced over time.

Hepburn Tropo prediction maps, weather maps and the VHF/UHK DX spot maps can be useful tools. It is worth announcing any trip to a hilltop via a social media channel.

Hepburn Index Tropo Map showing really excellent tropo conditions along the coast of Western Atrica


 Record Breaking contact between EI2FG and EA8CXN via Enhanced Tropospheric Ducting (Photo EI7GL)

Point-to-point communication is possible from high locations, and it will be necessary to have some map reading and compass skills. The beamwidths of 23cm yagi antennas are narrow and, if off by a couple of degrees over a long path, the desired station may be missed. It is worth announcing any trip to hilltops on the ON4KST chat or via the VHF, UHF, SHF Facebook pages.

Tropospheric scattering can occur from pockets of turbulent moist air and are characterised by a rough sounding signal. SSB and CW would be the choice of mode for this type of propagation. Another form of propagation is reflection from objects such as barns, grain silos, aircraft or even passing ships.

Aircraft scatter is one very effective mode of propagation. It is possible to track aircraft and take advantage of reflection from an aircraft traveling a given path adjacent to the two stations. Often this can result is some reasonable signal strengths which suddenly appear and last for a minute or two before they diminish. Such paths of aircraft can be tracked using the program “Airscout” by DL2ALF. Not too long ago, we had an interesting lecture on Aircraft Scatter with audio visual demonstrations, by Anreas Imse, DJ5AR.

 Showing reception of a Beacon over distance via Aircraft Scatter

Reflections from objects or structures, such as a barns or grain silos, can often result in an enhanced and unexpected path especially if operating at lower elevations. 

In one instance it was possible to reflect a signal from a passing cruiser resulting in a contact between two Spanish Stations who would not normally be in a line of sight advantage.

23cm signal Reflected from a passing Cruise Ship (Photo EI7GL)

There is much scope for experimentation on the 23cm band using different antennas, power levels, and portable locations. Provided you have a number of local operators to assist and give reports it will pave the way for DX operation at later stage. Even a small 2-watt transverter with a good antenna system will suffice and provide some excellent results into a 56 element beam. We are fortunate that there are at least eight operators capable of running equipment on 23cms in the Galway and Mayo areas. If you have the equipment contact the Galway VHF Group or Mayo VHF Group.

Friday, December 10, 2021

EI4GCG Galway Allstar Gateway


Galway 4 Metre Allstar Gateway Parameters

Frequency .................................... 70.425 MHz        

CTCSS Encode and Decode ....... 77Hz 

Power Output .............................. 20 Watts  

Antenna ...................................... 1/2 wave vertical

AllstarLink is a worldwide network of Repeaters, Remote Gateways and Personal Hotspots linked together via the internet and/or private IP networks. AllstarLink can run on a dedicated Linux computer or Raspberry Pi hosted at home or a remote site. Allstar is open source GPL software free for anyone to use.

Allstar Link has become popular on a worldwide basis and yet only one station existed in the Republic of Ireland with a further four located in Northern Ireland. The UK is well populated with Allstar Nodes and many are connected to the Supernode, UK HUBNET, which, in turn, connects many Repeaters and Gateways throughout the UK.

The quality of audio from the Allstar system is excellent and it is a user friendly system without too many commands.

Worldwide Distribution of Allstar nodes

There is a good distribution of Allstar Nodes around the world so a contact is always possible

There is a wide distribution of Allstar Nodes in the UK, however, very little in Ireland. The Galway Node only recently went on the air.

One excellent feature is the Bubble Connection map showing the node with all of its connections.

As illustrated there is a huge number of connections to the UK HUBNET node which is shown by the blue shaded bubble in the centre of the diagram. No excuses for no QSO after a call into this system.
 

The Galway 4 metre Allstar Gateway 

The Galway 4 Metre Allstar Node was easy to build using a M0AQC modified CM108 fob fitted into a plastic case. This connects, via a USB lead to the Raspberry Pi. A second lead connects to the radio bringing audio levels to and from the radio plus the PTT line and Carrier sense.


The TX Audio, RX Audio, COS, and PTT lines are brough out to a 15 pin accessory plug for connection into a Tait radio.

 
A Low Band Tait TM8110 was programmed for use on the Gateway. The radio was easy enough to program for one channel only with CTCSS Decode and Encode tones, power level of 20 watts and the various outputs and inputs from the accessory pins.

It is important to organise a cooling fan for the radio. The heatsink does get quite warm with a heavy duty cycle. Unfortunately radio amateurs do waffle on a bit!

The Asterisk Program, the controlling software, can be downloaded from the Ham VIOP Webpage where all the instructions for setting it up are included. 

Setting it up was not easy but if one follows the instructions from Ben Topham, G5REV, it is a good starting point. In this YouTube Video one will be 99% of the way to completion. Allstar Set Up The only other stumbling block is the set up of the Internet Router.

This is the completed set up which needs to be in a small rack with a coooling fan to force air across the heatsink. 

Prior to building the 4 Metre Allstar Node, a 70 Cm Personal Node was acquired from M0AQC, mainly to find out what activity can be found on  Allstar.


The only difference between the Allstar 4 metre Gateway was that a 70cm Baofeng 888S was modified to output a few milliwatts from the Driver Stage with the PA stage removed. This will give a good range around the home QTH. The Raspberry Pi was configured almost exactly the same way as for the Gateway. I used DCS Squelch on this systems as I was getting spurious transmission using CTCSS. This was courting some snotty remarks from the users of HUBNET and quite rightly so.

Ben Topham, 2E0BMT/G5REV, produces a complete kit of parts to build a 70cm Allstar personal Node. He also produced a 6 part YouTube video series showing a step by step build.

A picture of the completed G5REV kit

In this kit, one has to modify the CM108 fob and bring out leads for the Audio in and Audio out, PTT, and Carrier sense (COS). The Baofeng CM 888-S is stripped down and modified for low power use. Subsequent videos in the video series will cover the software set up and parameters to be set up in the Router.

Allstar Commands

 Mandatory Commands

*1 Disconnet from Link

*2 Connect to Node in RX Mode only

*3 Connect To Node in Transceiver mode

*4 Command Mode of Controlling node

 Optional Command codes

*80 Forces system ID

*81 Say System Time

*980 Say app_rpt Software version

*75 Link connect (Local Monitor only)

*72 Last Active node (System-wide)

* 71 Disconnect All links (Macro)

*74 Reconnect all links (Macro)

Note to connect to a node Always - *3##### where ##### is the node number to connect to

To Disconnect from a node Always - *1##### where ##### is the node number to disconnect from

Once one has successfully set up the parameters and software there is very little to operating Allstar. The audio quality is excellent although some operators do tend to over or under drive their audio levels. Make sure you have yours set right! This system is more active than EchoLink. It is possible to add Echolink to the software but it would be a retrograde step