In very simple terms, VHF / UHF Communications is a very vast subject and a simple article like this is not going to do it justice.
It also depends on how you were introduced to Amateur radio which could have been :
- You were introduced to VHF/UHF Communications as your first introduction to Amateur Radio and you have a health knowledge of the subject
- You have been used to UHF Citizen Band (CB) and already understand Repeater operation.
- You have been involved in VHF radio via Marine Radio or you are have been involved in the aeronautical industry using simplex VHF communications
- Via HF Radio (e.g. you were shown and intrigued by long distance HF Radio) and up until now that was all you were aware of.
These are just some common ones, and by no means the only way you were introduced.
If you have not done much work with VHF/UHF with Amateur Radio, then we need to understand a few important terms that are used (however they are not exclusively to do with VHF/UHF communications.
Simplex – On Radio A the transmitter and the receiver are set to exactly the same frequency, and likewise on Radio B the transmitter and the receiver are also set to exactly the same frequency. So if you look at Radio A and Radio B, they will all be on the same frequency. Radio A and Radio B need to take turns in talking and listening, they cannot both be talking at the same time (they can but they won’t hear each other). Most HF communications is generally (but not always) simplex operation.
Duplex – On Radio A the transmitter and the receiver are set to different frequencies, transmitting on one frequency and receiving on another. Typically this is used to talk to Repeaters, and the difference in frequency is generally called the offset
Half Duplex and Full Duplex – When you are running duplex, you have half duplex (one way at a time) and full duplex (two way at a time). Generally most radios are running half duplex when talking to a repeater, where as the repeater is talking full duplex. Most FM radios are half duplex only.
The most common use of of VHF/UHF radio is utilising Analog FM via repeaters, however there are also groups of Amateurs who look to achieve long distances just in simplex mode. They look for opportunities such as Tropospheric Ducting…take a look at this site for more information. https://www.dxinfocentre.com/propagation/tr-modes.htm and/or Multipath Propagation.
One of the advantages, particularly with 2m (VHF) and 70cm (UHF) radios is their cost. They offer a very low cost entry into Amateur Radio (as opposed to commercial HF radios, with a radio that will allow you to talk to other operators clearly, and with reasonable success, particularly in your local area, or the area reachable by your repeaters. In fact quite often in some foundation courses, they have a door prize of a VHF/UHF Handy Talkie (HT), and I have heard of one club providing a HT to every participant.
The next clear advantage is that it is relatively simple and low cost to build an omnidirectional or directional antenna for the VHF and UHF. As an example you can build an omni-directional antenna for less than $AU20 in a few hours, and that connects to a repeater over 50km away with a simple HT running 5w.
If you want to take this a bit further, you can enjoy the digital modes such as FT8 / JS8Call / SSTV / Winlink using a HT that costs no more than a decent restaurant meal for two (and that includes your audio interface).
And guess what, this is all done on your foundation licence. So if VHF/UHF sounds attractive to you, then dip your toe in the water
So we have talked about Tropospheric Propogation and Digital Modes with VHF/UHF radios, but we return now to the most common use of VHF/UHF radios and that is via repeaters. In simple terms, the repeaters help extend the range of your radio from the 50/60km to another 50/60km. and possibly further if the other party is using a directional antenna like a Yagi and/or they have higher power and/or they are located at a higher level.
To use repeaters, you need to set your radio with the correct settings. Their are several factors/components relating to the radio in order to connecting successfully to a repeater and these are :-
Set the correct RX Frequency on your radio – when you look up repeaters in a repeaterbook or on a club website, they list one frequency for the repeater. This is the repeaters transmit frequency (or downlink frequency), and this is the frequency you should have setup as the RX frequency on your radio.
Set the correct TX Frequency on your radio – again when you look up repeaters in a repeaterbook or on a club website, they will list an offset which will be listed as a positive or a negative. These offsets may vary from band to band, so it’s best to confirm what your offset is. This offset is applied to your radio as the TX frequency (in other words, your repeaters receive frequency or uplink frequency.
In many cases, you are going to need a CTCSS (Continuous Tone-Coded Squelch System) frequency as well. Many repeaters require this, however there are Open Repeaters in use in Australia (no tone required), but they are becoming smaller in number as repeater owners are trying to reduce interference from other devices. This tone is transmitted when you key your radio and is a sub-audible tone that keys the repeater to repeat your transmission.
Being within range of a Repeater/Possibly external Antenna. This one is important, particularly if you leave in an area covered by hills and mountains (e.g. not flat terrain), and you are a fair distance from a repeater, you may need an external antenna. If you are not sure first, then find out where your nearest repeater is, drive close by and test your connection to the repeater. If this works, and you get back home, and it doesn’t work, then time to look at building an external antenna (and there is no harm in getting a few metres height out of the build as well)
As an example, lets look at a repeater out at Mittagong, NSW with a call sign of VK2RHR
If we look at the shortform details we have the following
- Repeater Call Sign : VK2RHR
- Repeater Frequency : 146.82500 Mhz
- Repeater Offset : -0.6 Mhz
- Repeater CTCSS : 91.5hz
- Repeater Mode : FM
As you can see we have all the information we need to setup our radio to talk to this. In many cases, your radio would have come with a programming tool/software (CHIRP is a common one), and you would setup “channels” on your radio with these details, so these details could be entered in as Channel 1 and would be set as the following
- RX Frequency : 146.82500 Mhz
- TX Frequency : 146.22500 Mhz (Calculated using the -0.6 Mhz offset)
- CTCSS : 91.5Hz
- Mode : Analog/FM (if your radio is only analog FM, you don’t need this)
If you complete this successfully, you can give it a go, or if you want to have a listen first, within 10 mins, you should either hear a call or if it is quiet, you should here the repeater send its call sign in CW. If you hear this, then you know that you are at least in receiving range (remember that a repeater might have a higher power output than your HT, so this does not necessarily translate that you can reach it on the transmit.
If you want to transmit, just remember this is different from CB (if you came via that track), and its not the same as HF (if you are well versed in HF etiquette). The whole premise is in efficient communications, so generally you would not call CQ CQ CQ this is VK2XXX and repeat several times. with VHF/UHF communications, you generally do not have an operator on the other end sweeping the dial listening to CQ’s. Most VHF/UHF have a set channel or set number of scanning channels (particularly as many are mobile/in vehicle devices).
- So to transmit, first listen to see if anyone is using the frequency/repeater but give it a minute if you can
- Then you simply just say VK2XXX listening and listen – if no response then repeat again. If someone is on frequency/Repeater they will answer you.
Main things to remember is
If someone is talking and you want the channel, you will need to wait till they are complete.
If they are talking do not break in over the top, wait till a pause in their handover
If you believe they have finished, but did not call clear, just politely transmit and ask if they are complete. Most times it is a mistake that they have not called clear, and a gentle reminder goes a long way.
Do not Key the microphone without calling your call sign. It is a regulation requirement that you provide your call sign when you commence a transmission, and at least again every 10 minutes of a conversation. So a quick key down is a transmission and should include your callsign…..even this simple line will suffice
VK2XXX testing
It will meet the regulation requirements, as well as inform anyone else that you are not hanging onto the channel.
Note : This is very different to Digital VHF/UHF (DMR/DSTAR/YSF) where a kerchunk is used ( a PTT press) to open a talk group through a repeater. This because when you perform a kerchunk, it passes the Callsign and therefore meets the regulation.
This is by no means extensive, just the basics of VHF/UHF communications. Digital VHF/UHF is another kettle of fish and you will find an article on this Website that discusses this in more detail.
One more important note for foundation members, you may note some good quality, but low priced brand name VHF/UHF Analog FM units on some classified sites or forums. You need to check that they do have the CTCSS capability, otherwise, the only repeaters you will be able to utilise are the OPEN repeaters. To be fair, most of these ads from Ham Operators normally clearly state that it has no CTCSS capability,
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