GENERAL INTRODUCTION

        This page is being developed as a result of Justin, G8YTZ, installing GB3OO digital amateur television repeater located at Paddlesworth near Folkestone, Kent. It is intended as a relatively straightforward guide for beginners who have not tried ATV before and are interested in finding out the basics for reception.

         GB3OO is currently the only ATV repeater in Kent. Like most repeaters, it accepts input on one frequency and re-transmits it on another. However, unlike most repeaters, GB3OO does this on two separate bands, 70cm (437MHz) to transmit to it and 23cm (1304MHz) to receive back from it, polarisation is horizontal both ways. This repeater can also be accessed and viewed via internet streaming and has many additional features.

    RECEPTION

         There are two methods of viewing GB3OO, directly off air or via internet stream.

         Most radio amateurs will want to see if they can receive off air. The signal is pretty strong in much of east Kent in particular, so direct reception shouldn't be a major problem even with fairly basic equipment: A satellite receiver/TV and an antenna. In some locations an RF pre-amplifier (more info to follow shortly) may be needed too. The satellite receiver needs to be DVB-S2 capable, but be warned, many 23cm antennas are a DC short and a satellite receiver will probably have voltage on the aerial socket for an LNB. This can usually be switched off in the menu somewhere. Keep in mind this can also be an issue if using an in-line satellite RF amplifier as they throughput the DC for the LNB.

         OK, you have your DVB-S2 satellite receiver connected to a 23cm horizontal antenna and TV. Point the antenna in the direction of the repeater. Select Astra satellite 19deg. in the list and DVB S2 if given options. A blind band scan search by the receiver might find the signal from GB3OO, but it might not, in which case try setting up for a new transponder. This is the only awkward bit. Go into the transponders list and delete all existing transponders if you wish, select 'new' and input the required parameters: choose LNB type KU 9750/10600, 2MS/s (you may have to put 2000 as the units are often kS/s) and FEC 3/4, the frequency to enter is 11054 (this is because the receiver will be expecting a satellite frequency, rather than the IF frequency of 1304, however, some may have this option), select scan and save. If nothing is found the antenna may be pointing the wrong way or the signal is simply too weak or even not on air.

         Other receivers are available (e.g. from the BATC shop), but these tend to be expensive and involve a certain amount of homebrew construction. A cheap satellite receiver (around 20GBP) from Ebay is perfectly satisfactory for 23cm ATV.

         To check out what GB3OO is doing on the internet, go to the BATC website (you don't need to log in or register), select 'streamer' then 'GB3OO' from the list. There is a considerable delay in the stream compared with direct RF reception.

   ANTENNA

         What to do for an aerial? There are several options. The antenna shown at the EKRS talk, 70/23cm, for TX and RX, is expensive, by the time you've included Ebay fee and P&P close to 150GBP. Who would want to pay that as a starter, not knowing if reception at your QTH would be ideally suited? You may already have a 23cm antenna, used for other modes of course. Or you could homebrew something, even a simple open half wave dipole or small beam maybe. A redundant satellite dish with a dipole at the focus. Re-scale an old (or new) UHF TV antenna (we are investigating this). A broad band antenna is not really required, so a normal open dipole should suffice and avoid issues with short circuiting the RX input DC or in-line amplifier. An easy to construct small antenna is the bi-quad (or more) loop, these also are good for dish feeds (but are a DC short). If a DC short circuit antenna is an issue, a small (1nF) capacitor with very short leads in series with the coax centre conductor readily solves the problem, easiest done at the driven element. G8PPQ has constructed an excellent 23cm beam to a very high standard.

         A brilliant simple program for calculating dimensions for homebrew beam design can be found at VK5DJs website, go to the Home page > Downloads> scroll down to Yagi Calculator> Download Yagi Calculator Version 3.0.1 and then setup once downloaded. Or we can send you the setup file, use contact details on this sites Home page.

    TALKBACK