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| 23 cm ANTENNAS |
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| At 1300 MHz, the Yagi antenna is more efficient than a Dish, and is readily available. A 15 element Yagi with 10db gain costs around £20. A 38 element Yagi with 14db gain,about £32. The 55 element TONNA is around £80. Others are available from Sandpiper Communications. (For antennas see useful addresses.) |
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| ANTENNA FEED CABLES AND PLUGS |
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| Down lead cables should be 50 ohm Westflex 103, for |
| minimum losses. At 1300Mh the signal loss is around 2db per 10 metres with this cable. UR67 or satellite cable are nearly twice the loss of Westflex. For connecting do not use PL259 plugs as these are useless at this frequency. 'N' type plugs should be used at the antenna end and on Mast Head Amps, whilst 'F' plugs are acceptable for in-line amps and at the receiver back panel. |
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| RECEIVER TESTING |
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| When ready for tests, contact a transmitting operator who will be pleased to provide test transmissions. Find someone near you from the list of stations elsewhere in these pages. To help you conduct your tests, here is the normal picture reporting system referred to as 'P' numbers. |
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| P0 = Total noise, no picture but sync bars detectable |
| P1 = Picture locks on sync, but is weak with high noise P2 = High noise, fair picture, fair detail. |
| P3 = Noise visible, strong picture, fair detail. |
| P4 = Slight noise visible, very strong picture. P5 = No noise visible, studio quality, excellent detail. |
| When testing your antenna installation, you will have quickly realized that a beam rotator is essential unless you intend to carry out tests with one station only. |
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| THE TRANSMITTER |
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| For the 23cm ATV Tx, the one watt FM/TV transmitter supplied in kit form by the Worthing Group is recommended. This kit costs Stg£85+ £2.50 post and packing .(Feb'2000 price). The Tx has a die cast box, tuning control, video in, audio in, 12 volts in and RF out. You can set the sound/vision spacing to 6 MHz on the kit so that inter carrier sound can be received when using a domestic TV at the receiving end. |
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| Assembly is a little fiddley around the few tiny surface mounted caps, and requires a very small iron bit to succeed here. If you are happy with this, then the unit is a very good starter Tx, and with one watt will give good signals for a 20 mile radius or more, and is the perfect unit to drive the 15 or 20 watt RF Amps that are available. |
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| If you are not happy to tackle fiddley pcb assembly, Fully assembled ATV Tx's and Rx's are available for both 23cm's and 3cm's from WYZCOM in Belfast. But you do have to pay for the convenience of fully built items. Their price list and details can be found on their Web site at, WWW.WYZCOM.COM along with an ATV picture Gallery showing many pictures of Irish and Welsh stations in operation including off air shots. |
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| With RX and TX ready for operation you must decide what antenna system to use.That is, will you have two antennas ?, one for each unit, or will you have one ant' switched between each unit. Opinions differ according to what gear is to hand .. An RF change over switch can cost as much as an extra antenna....If a supplier can be found. Note that if a switch is used, it will need to be positioned at the antenna side of any Mast Head amp used, as the Tx RF must not pass up through the Amp of course. |
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| THE VISION SIGNAL |
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| Many people, or their families, already have either a camcorder or a video tape recorder available. There are cheaper ways of obtaining video signals but a camcorder is the most versatile. If you have just the VTR, then get the help of a camera equipped friend to help you to pre-record your test signal. This could consist of a few minutes tour of your shack, followed by a home made test card including your callsign.This will provide a useful start that can be used for each new contact. Other video sources are Bar Generators, security cameras found at rallies or computer generated test cards. |
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| There is an excellent computer program available for any Amiga with 1 Meg or more memory. The program has 56 test cards, text for 30 screens of messages, and scrolling facility for a moving message. Also a QRA calculator that gives you distance and beam heading to the station locator that you enter in. This is a three disc set available from the Worthing Group at Stg£10 + 75p postage. This is an ATV must......if you have an Amiga. |
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