5.6 GHz

Introduction

It has just become very easy (and low cost) to get on the air on 5.6GHz (the 6 cm amateur band) using the cheap modules intended to transmit “First Person Video” (FPV) back from drones to their operators.

These units can be used without any modifications to get on air and with a simple wifi plate or dish antennae and a clear line of sight path be used to can send pictures to stations using the same equipment over 50 Kms away.

Frequency choice

The UK amateur band plan is shown on the RSGB website here: https://thersgb.org/services/bandplans/html/rsgb_band_plan_2017.htm

GB3KM has a licensed input on 5665 MHz and this has been chosen as the primary ATV operating frequency.

The FPV equipment receive and transmit frequencies are set using DIP switches, and most tune to this frequency but care needs to be taken when selecting equipment to make sure it does cover this frequency.

Equipment

The FPV units are widely advertised on eBay with titles similar to “Tarot 5.8G 600MW Telemetry TX/RX Combo for FPV Image Transmission TL300N” and are available at reasonable prices. The typical units are very small but have reasonable FM-TV performance with a quoted spec of 600 milliwatts out and receiver sensitivity of -80 dBm. Amplifiers are available to raise the output power to 2 watts or more.

Mounting the equipment

Due to the very high losses in co-ax cable at 5.6GHz it is recommended that you mount the units very close to the antennae and run 12v DC and Audio and video back down the cable to the shack or operating position. Also whilst these units are very small but do run very hot in operation and it is suggested you provide a good heatsink for both Tx and Rx - mounting them in a diecast box on the back of the antennae is ideal.

Detail of G8GKQ transceiver setup is shown here (receiver unit on left & transmitter with fan on the right)

Antenna change over relays

The FPV equipment comes as separate Tx and Rx units. In order to operate on a single aerial, you will need an antennae changeover relay, however the losses at 5.6GHz can be significant and care must be taken when wiring up the units to ensure RF cables are of good quality and kept to a minimum length - semi rigid cable with SMA connectors are ideal.

PL259 and even BNC connectors are very lossy at 5.6GHz and should not be used but the surplus SMA relays often available at rallys are ideal for 5.6 GHz.

If no suitable relay is available It may be cheaper to use a separate antenna for receive and transmit as shown in the picture below.

Reverse SMA

Be aware that all the 5.6GHz FPV units are reverse SMA (like wifi equipment) and all low loss cables, unless bought specifically for the purpose, and suplus SMA relays are almost certain to be standard SMA connectors and will not fit. Adapters from reverse to standard SMA are available on ebay or other suppliers.

24v relay operation

Most of these relays are often 24v coils - use a switching regulator from ebay as shown in the picture (search for step up buck regulator) to boost the 12volts on transmit to 24v.

Antennas

As 5.8GHz is also used by broadband wireless networks, there is a wide choice of antennae available for use on 5.6GHz ATV. This can range from flat plates to wire mesh dishes as seen in the above pictures.

It is also possible to use a satellite mini dish with a suitable feed such as a wave guide horn to the design by G4NNS - the picture shows a Sky mini dish fed with a WA5VJB log period PCB feed (available from G4DDK).

Video equipment

Rx

The receiver will need to be directly connected to a composite video input monitor to view the received the signal - normally on a yellow phono or RCA connector. Beware of using modern flat screen monitors which have a video squelch which will not display noisy signals and just give a blue screen until they get a strong video signal.

There are a number of circuits around to defeat the squelch.

Tx

An old camcorder with a yellow phono video out socket is an ideal video and audio source for the transmitter but don't forget you will need to display your call sign to remain legal. This can be a video generator, a jpeg card reader with video out, the Portsdown system with video out or a piece of card with your call sign scribbled on it!

On the air

Using dish aerials of 30 – 60 cm line of sight ranges of 80 km can easily be achieved. P5 (noise free) FM ATV pictures have been exchanged over an 138km path using the equipment pictured - the picture below shows G4COE being received over a slightly obstructed 66Km path.

Horizontal polarity has been chosen as the standard and dishes typically have a beam width of 4-8 degrees.

Activity hot spots

Know users include:

• Southern England = G8GKQ, G8GTZ, G0UHY, G8XZD, G4UVZ, G3VPF
• Dunstable area = M0SKM, G4CPE, G0WFT
• North-east = GB3KM, G1LPS, M0DTS
• Cheltenham = G0LGS, M0RKX and G4NZV (using WB audio only)
• Bolton Wireless Club = G4JLG, M0UFC, MW1FGQ, G6GVI (PW “Siren” Article)
• Hereford = G8XYJ
• Yorkshire = G8BYN
• Norfolk = G4NJJ, G8AJN and M1BKF
• Cumbria - Barrow in Furness radio Club project

More information

Dave G8GKQ did a presentation at the BATC annual convention CAT17 in September 2017 on getting started on 5.6 GHz ATV.

• The presentation is available here https://wiki.batc.tv/images/9/94/CAT17_Portsdown_Update.pdf
• The video of the session is available on the BATC youtube channel here https://www.youtube.com/watch?v=XJzGNsGmE9Y

There is a thread running on the BATC forum where the ATV community are exchanging ideas and also posting results of the latest on air tests. http://www.batc.org.uk/forum/viewtopic.php?f=2&t=5026