Hosted by Tom O'Hara W6ORG - Email:
Retired owner of P.C. Electronics, The Leader in Amateur Television Equipment for 50 years - history
This chart will give you the expected line of sight DX on the 1240-1300 MHz ham band for AM ATV given transmitter peak envelope power (sync tip), coax loss and antenna gains on both ends.
Total gain in dB = sum of Transmitter antenna gain in dBd (gain over a dipole) plus Receiver antenna dBd gain minus transmitter and receiver coax losses. Figure 1 dB coax loss per 16 feet for Belden 9913, 21 feet for Times LMR-400 and 33 feet for Times LMR-600. If 4 MHz deviation FM ATV add 12 dB; if your downconverter or preamp noise figure is more than 2 dB, subtract each dB above 2. For power levels inbetween the diagonal lines, add or subtract dB's - ie. add 3 dB each time you double the power.
The power level diagonal lines were chosen to reflect the output of our 50-100 mW TX23-.1s Transmitter or added Downeast Microwave linear amplifiers. The older 3 watt RTX23-3 AM ATV transmitter would add 4.7 dB to the total gain when using the 1 Watt line. Check eBay and QRZ.com On Line Swapmeet for our older models.
Example #1: AM ATV repeater transmitter running a RTX23-3 driving a 2318PA Downeast linear amp, 100 ft Belden 9913 coax, Diamond U200 omni being received by a Directive Systems 2424LYRM Loop Yagi, Downeast 23LNAWPQ antenna mounted preamp and TVC-12S downconverter.
Example #2: A FM ATV point to point link using a Videolynx Z23B driving a Downeast 2318PA and OAL OAL TCR-23cm corner reflector to transmit, receive with a 2424LYRM Loop Yagi, antenna mounted Downeast 23LNAWPQ preamp and a 23/33FMR-3 receiver.
Coax loss is very significant at 23cm. It might be cheaper to invest in larger lower loss coax depending on the length, than a higher power amplifier. For instance, Belden 9913 has about 6 dB/100 ft of loss, LMR-400 about 5dB/100 and Times LMR-600 has 3 dB/100ft. Going from LMR-400 to LMR-600 is less cost than going from the Downeast 2330 amp to the 2360 amp.
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