It is 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, can be used to can send pictures to stations using the same equipment over 50 Kms away.
- 1 Frequency choice
- 2 Equipment
- 3 Antenna change over relays
- 4 Antennas
- 5 Video equipment
- 6 On the air
- 7 Activity hot spots
- 8 More information
- 9 Technical information
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 licenced input on 5665 MHz and this has been chosen as the primary ATV operating frequency. Audio WB-FM operators have been using 5825 and 5840 MHz. 5825 MHz is too close to the band edge for ATV, and 5840 MHz is marginal.
The FPV equipment receive and transmit frequencies are set using DIP switches, and most tune to 5665 MHz but care needs to be taken when selecting equipment to make sure it does cover this frequency. Example channel tables are shown at the bottom of this page.
The FPV units are widely advertised on eBay and other sites 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.
Be aware - we have found that on some rx units, the video out is on the Red phono lead and not the expected Yellow lead!
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 long 12v DC and Audio and video cables back down the cable to the shack or operating position.
Also whilst these units are very small they 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)
Whilst the basic units work very well and have been used to transmit over 60 Kms, power amplifiers to boost the 600mw transmitter signal to 2 - 4 watts are available from several suppliers on ebay and other sites and will significantly increase the distance the units will work over. These should be connected after the transmit unit but before any antennae change over relay and remember that his will increase the volt drop on any long 12v cable feeding the transmitter at masthead.
Several users have found these PAs to be "fragile" and you should always make sure the antennae is connected and all connectors done up tight before applying power.
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.
See this wiki page for more details on suitable relays, 24 volt operation and 4 port or transfer relays.
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 - note the Tx and Rx units are mounted directly on the back of the flat panel antennaes.
Be aware that all the 5.6GHz FPV units use reverse SMA connectors (like wifi equipment) and all low loss cables, unless bought specifically for the purpose, and surplus SMA relays are almost certain to use standard SMA connectors which will not fit. Adapters from reverse to standard SMA are available on ebay or other suppliers.
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 - see here for construction details: http://myweb.tiscali.co.uk/g4nns/FeedHorn.html
Horizontal polarity has been chosen as the standard (wave guide needs to be vertical when feeding dishes) and dishes of this size typically have a beam width of 4-8 degrees.
DIY Biquad antennae
This web page http://buildyourownantenna.blogspot.co.uk/2014/07/double-biquad-sector-antenna-for-5-ghz-wifi.html has a well engineered double Biquad antennae with 13dBi gain.
Note in the picture G8JAN has directly connected the Tx module to the antennae to avoid co-ax losses.
The receiver output 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.
Video squelch defeat
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 and also improve the readability of the signal.
- Syncsmurf by PE1RQM - kits are available details on the webpage here.
Results are very impressive:
- eachines FPV recorder
Several people have reported that they are using these devices, available from various sites, and as well as defeating the monitor blue screen by inserting syncs on noise they have a single push button record facility. They record to an SD card which can be removed and the files viewed on a PC but users report that you need to use a good SD card and have had problems with Kingston and Sandisk are preferred.
- CQ-TV 129 included details of a Video sync processor:
- Or any video sync processor may be useable such as the Advanced Converter Enhancer used by many stations on 23cms FM.
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, or a piece of card with your call sign scribbled on it!
Alternatively the BATC Portsdown project can be configured to deliver composite video and audio out from the Rpi multi-jack plug. This can be test patterns, Rpi desktop or the Portsdown camera and microphone - see this wiki page for more details.
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 described on this page - the picture below shows G4CPE/p on Dunstable Downs being received at the Ridgeway near Didcot over a slightly obstructed 66Km path.
The current UK "record" for a contact using standard FPV units stands at 138 KM from Dunkery Beacon near Minehead to Cleeve Common near Cheltenham.
The picture shows G8GTZ/P received by G8GKQ/P over the 138Km path.
FM voice only
Several stations in the Glouscester and Bolton area are using these units for wide band FM voice only - this is achieved by simply putting high level (1v p to p) audio on the yellow video tx phono and listening with a powered amp on the yellow Rx phono amp.
As it is using the same bandwidth rx and tx system, performance will be no better than FM video - ideally the 480MHz rx IF would be tapped off in to an SDR or narrow band receiver to give significantly enhanced (+20db?) narrow band performance.
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)
- Ludlow, Shropshire = G8XYJ
- Yorkshire = G8BYN
- Norfolk = G4NJJ, G8JAN, G4WVU and M1BKF
- Cumbria - Barrow in Furness radio Club project
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
The large rx chip in most units has got the part number removed, however it appears that a lot of receivers use the SM201R module. The spec and pinout are shown below but notice the frequency range of this particular unit does not seem to cover 5665MHz so make sure the one you buy does!
S meter output
Looking at the above table it appears that the RSSI is available on pin 17 of the SM201R and could potentially be used for a signal strength meter to help align the antennas when setting up a QSO.
It also appears that the SM201R uses a 480MHz IF (same as the Comtech) and potentially could be modified with narrower filters to improve RF performance.
Tx and Rx perfomance
Initial measurements suggest the Tx bandwidth is 25 - 30 MHz.
This accounts for the quoted Rx sensitivity at -80dBm which may be improved by an LNA but will ultimately be limited by the Rx IF bandwidth.
As mentioned above, the channels settings vary from manufacturer to manufacturer. This table is taken from the Tarot data sheet which uses the SM201R module but does include 5665MHz:
And this is the table for the Eachine TS835 transmitter:
This table is from a "Fat Shark" transmitter that does not cover 5665 MHz: