Practicals Page 2

A quick Reminder of the Practical’s covered on this Page :-

5) Demonstrate the use of a HF Radio transmitter / receiver to tune in to a SSB voice contact and a CW ( Morse ) contact.

6) Make a HF, SSB contact. Demonstrating Frequency, Receiver Incremental Tuning ( RIT ) Audio Gain, RF Gain, Microphone Gain and Antenna Tuner ( ATU )

The HF practical’s can be a little daunting at first. Unlike the VHF practical’s. You will probably have a QSO with a stranger. This adds unpredictability. You cant really be sure how it will go. Try not to worry, most amateurs are very friendly and like to help. We covered the Basic CQ in the VHF practical so im going to focus on other things here.

What does it all mean ?

There is a few new topics here, the first one is SSB. This stands for Single Side Band. It is a type of A.M.( Amplitude Modulation). In a normal A.M signal we have a carrier and two copies of the information ( voice ) These copies are positioned one below and one above the carrier. Called the Upper Side Band and Lower Side Band.

AM-mod
The above image will hopefully give you some idea of what we are talking about. When we use SSB ( single Sideband) modulation. The carrier and opposite sideband are filtered out. This is much more efficient, instead of the power being split between the carrier and sidebands. Which are filtered out in the receiver anyway. We only transmit one sideband.

RF Gain : Radio equipment is built to produce a certain level of RF power. For HF equipment this is typically 100 Watts. The RF gain is a control that lets us alter the output power. Often from 5 watts up to the maximum.

RIT ( Receiver incremental Tuning ) : This control can be invaluable on HF. Modern equipment is built in the form of a transceiver. That is a Transmitter and Receiver in one. When we transmit on HF our signals travel into the Ionosphere. This can alter them. Sometimes changing there frequency. So The person receiving them on the other side of the planet, sets their radio to a slightly different frequency to us. They then transmit back. We receive it and have to change something. You may think, why not tune into the same frequency as the guy on the other side of the planet ? The trouble here is that when we transmit, the ionosphere affects our signal again. Forcing another change for the person on the other side. We need a better solution. That is where RIT comes in. It lets us transmit on one frequency and receive on a slightly different one. So we transmit and leave our frequency alone. Then if a change is needed. We adjust the RIT. Not the transmit frequency.

Audio Gain : This is the volume control for the receiver.

Microphone Gain : All microphones are slightly different and as Radio equipment ages, things change. If we find the quality or strength of out audio is poor. We can try and adjust the Microphone gain. Too much or too little can have a very negative affect. We need to find the best setting. This is easiest done with the help of another amateur. Who can tell you how your settings are changing your quality.

ATU : Antenna Tuning Unit also known as an Antenna Matching Unit . Is a device used to help match an Antenna to Radio Equipment. This are very common for HF radio. HF contains. several bands, all requiring large antennas. So it normally becomes necessary to use one antenna for several bands. This is achieved with an Antenna Tuning Unit.

A good guide to operating on air can be found here : http://thersgb.org/services/education/downloads/pdf/good-operating-practices.pdf

Comments are closed