13 cm radiolink budget analysis

I discovered that the video signals from my 2 Watt 13 cm transmitter reach the PI6ZTM repeater, normally producing an acceptable picture.

A link budget analysis can be made for this signal path:

Transmitter side (36.9 dB)

Transmit power: + 33 dBm
Note: Pdbm = 10.log (1000.2W)= 33.01

Cable losses: -4.1 dB
Note: consists of
- RG/6U; 34 dB/100m => 3.4 dB (for 10 m)
- Mismatch due to use of 75 ohm coaxcable: swr = 75 ohm/50 ohm = 1.5 => additional losses: 0.2 dB
(ref. www.deman.in.nl/Antennas/Voedingslijn/VERLIEZEN%20BIJ.pdf)
- Connectorlosses 0.5 dB

Antenna Gain: 8 dBi
Note: biquad homemade

Receiver at PI6ZTM repeater site (87 dB)

Antenna Gain: 10 dBi
Note: estimation waveguide slotted antenna

Cable/connector losses: - 3 dB
Note: rough estimation

Sensitivity threshold receiver: -80 dBm 
Note: rough estimation


Propagation (-116.1 dB)

Propagation loss: -116.1 dB
Note: Friis formula: Lp=92.45 + 20.log(F) + 20.log(D)
F in GHz and D in km makes:
Lp=92.45 + 20.log2.4 + 20.log6.3 = -116.1

Now we can calculate the link margin:

(Transmitter) + (Receiver) - (Propagation) = 36.9 + 87 - 116.1 = 7.8 dB

This value is within the range of 6...10 dB which is required to obtain a good radio link ('rule of thumb').

Note: The receiver sensitivity, cable/connector losses and antenna gain at the repeater site are estimates. The receiver (in fact converter) is mounted a few meters from the antenna hence cable losses are not that high.

http://www.pi6ztm.nl/index.php/gezien-op-pi6ztm