ISG 2.4GHz RF Video Link Receiver and Monitor for thermal cameras

[Fraser]

Something different from thermal imaging cameras from me, but still thermal camera related 

Firefighting thermal camera manufacturers have been in the habit of offering users of thier equipment the option to relay thermal camera images from the front line user back to the command posts that is co-ordinating the operation. This offers situational awareness for the command team. This capability is used in both real fires, emergency sitations and during training, where the training instructor needs to monitor student use of the camera. The link from the thermal camera is normally RF based as long cables are a hindrance and impractical ! The Nature of the RF link varies but includes, Plain FM Video transmission, Robust Digital links and even Wi-Fi. The link may be 'in clear' or encrupted, as required by the user. Frequencies vary and are often dictated by regional licencing reguations. Common bands used are 1.3GHz and 2.4GHz. The transmitter is either built-in to the thermal camera or offered as a user installable external 'pod' that may be attched to the camera. Some transmitters are located in the optional handle or in a special battery pack.

I stumbled upon the receiver side of such an RF link that was produced by ISG for use with their thermal cameras and those of other manufacturers. The unit contains both the 2.4GHz receiver and a 3.5" colour TFT LCD monitor in order to provide a complete mobile monitoring solution. The unit does not have its own batteries and is powered from either 240V or a 12V vehice supply. A video output is provided for the use of a larger monitor, if desired. The receiver provides two user selectable channels and may be configured for PAL or NTSC. Inside the unit there are controls for brightness, contrast, video output level and image orientation.

As will be seen in the attached images, the unit is supplied to ISG by Rotronics UK and it is built to high standards. Black 'aviation' aluminium is used for the casing and this construction resembles other professional military and civilian equipment that I have used. The unit orignally cost around £2500.

An interesting design feature of this units monitor is that the LCD panel is angled for optimum viewing angle with the unit sat on its rear. The antenna socket is on the side but all other I/O and controls are mounted on the front as is not uncommon on equipment intended to be mounted in a bag or control panel.

I am currently sourcing a suitable transmitter to work with this receiver and thankfully such are relatively common as standard frequencies are used. Some ISG cameras come with such a transmitter built into them so it is worth checking.

The two RF link receiver frequencies are 2.454 GHz and 2.470 GHz

Fraser

 

[Fraser]

User manual pictures in case it is needed in the future by anyone 

[Ultrapurple]

I have numerous transmitters that may well be suitable. I'll contact you direct.

[Vipitis]

use an off the shelf FPV/drone transmitter/receiver. Plenty of options available.

If you want really high end, get a TerraDeck, at which point a wifi solution might be better.

[Fraser]

The transmitter that is used in ISG Elite cameras is the K&A VideoBlaster "VBLAST2400" and associated compact antenna PCB, as shown in the top right of the attached picture from a fellow forum member some time ago.

I attach the FCC approval images for interest.

[Bill W]

The transmitter that is used in ISG Elite cameras is the K&A VideoBlaster "VBLAST2400" and associated compact antenna PCB, as shown in the top right of the attached picture from a fellow forum member some time ago.

I attach the FCC approval images for interest.

By default the VBLAST would be on the 'fire' FCC Part 90 frequencies 2458 / 2474, yet for your receiver it quotes 2.454 GHz and 2.470 GHz. 
Maybe it does not matter or is a centre vs zero deviation value ?

[Fraser]

Bill_W,

This is what I find confusing with 2.4GHz video transmitters. I see many different frequencies mentioned in transmitter specifications . I am used to seeing unmodulated carrier frequency and frequency deviation specifications. Then there is the allocated channel specification but that is of limited use as the transmitter is the active emitter within the channel so it’s specification takes priority. I would normally expect the transmitter and receiver specifications to match. In my experience, however, some receivers have a large capture range and their AFC locks onto the transmitter signal provided its frequency is not too far off what is expected. Most of the 2.4GHz video transmitter kit I have seen on budget video link installations is of questionable quality and frequency stability. The high end video transmitters that I used were on licensed frequencies so had to meet their specifications and were built to the standards found in professional PMR etc. Sadly licence free bands can be a bit like the Wild West when it comes to equipment quality ! Some is very good because the designer is used to working with quality licensed kit and some is verging on criminal in its spurious emissions and frequency drift. Having looked at the K&A transmitter designs, they seem to sit in the middle ground so are fit for service but nothing special….. built to a reasonable cost I suspect. I will delve deeper into this frequency specification issue. Ultrapurple is very experienced in this particular video transmitter/receiver realm (as well as others!) so maybe he has some insight into the frequencies stated by manufacturers of 2.4GHz kit ?

Fraser

[Ultrapurple]

For at least the last 20 years to my certain knowledge the standard 2.4GHz videosender has used a synthesised transmitter. These actually have reasonably good frequency accuracy - well within 1MHz of nominal is normal - and good-enough stability. If you listen to one on a narrowband receiver you'll hear it wandering around a few kilohertz but that's all.

Here's a close-in phase noise plot of a 1.2GHz transmitter based on identical technology, done some 20 years ago:



These transmitters all use FM, and some may have one or two sound (or maybe telemetry) subcarriers at typically +6 and +6.5MHz (+ because they're subcarriers modulated onto the FM centre frequency so they appear both above and below the carrier). Here you can clearly see the two subcarriers, roughly 30dB lower in amplitude than the carrier:



So you can take it that the transmitters are going to be pretty good.

On the receive side, it very much depends on what the designers decided upon. Most use(d) the same type of synthesiser as the transmitter and, at that time, 480MHz IF. Capture range was small, no more than 2-3MHz either side of the nominal frequency - and that was only for strong signals. Weak signals had to be more or less spot on frequency to avoid major sparklies like this example:



Putting the receiver spot-on the transmit frequency (within 0.5MHz or so) cleaned up the video significantly: this was exactly the same receiver with exactly the same off-air test signal but tweaked very slightly to put it spot-on:



My best guess is that the ISG gear was built with very similar technologies, as that's the era it's from. More modern analogue video transmitters use more tightly integrated (and much smaller and hotter-running) transmitters. I haven't disassembled a recent receiver to find out whether they are still analogue or are now demodulated digitally.

Why use analogue for these links when as we all know digital TV is so much more bandwidth-efficient (offering a good picture in <2MHz bandwidth compared to ~20MHz for analogue)? Probably because analogue never, ever, 'freezes' so there's no chance of thinking the camera is just pointed at a static scene when in fact it - and the fireman holding it - has plunged through a failed floor into the basement. On analogue you'd see the signal disappear and maybe get occasional snowy/sparkly frames, whereas on digital you'd (probably) just see the last good frame, or maybe a blue screen.

[Ultrapurple]

Returning to Fraser's original question about frequencies, these were generally region-specific. Roughly 2.40 to 2.50GHz has long been internationally allocated as an ISM (Industrial-Scientific-Medical) band where many different systems operated - and operate - in cheerful chaos: 2.4GHz videosenders have largely died out because they use the same band as Wi-Fi and the systems suffer mutual interference; Bluetooth uses the same band too, as do microwave ovens (2.45GHz). Even radio amateurs will be found there, thanks to a relatively recently launched geostationary satellite with an amateur radio payload that lets hams as far apart as South America and Sri Lanka talk to each other and even send live video. And in years gone by British and other police forces used unencrypted analogue video transmissions for what became known as 'heli-telly' - their airborne visible/thermal search / track cameras.

Generally speaking the 100MHz of available ISM spectrum will just about support four analogue video channels, though three is more comfortable. So you immediately have two different channel sets. Some systems operated just above 2.5GHz - the ITN and BBC News helicopters, for instance, both used to transmit analogue FM video, usually back to the Post Office Tower, if I remember correctly, for stories within 100 miles or so of London. So a few more channels there.

Overall there is no universal band plan or channel allocation for 2.4GHz analogue video transmitters, however it's likely that whatever frequency the transmitter label says it's on is pretty close to the truth.

[Fraser]

Ultra purple,

Many thanks for the excellent insight into 2.4GHz analogue video transmission. You also explained why I saw so few 2.4GHz analogue video transmitter modules on eBay when I looked. My Receiver unit is Police Surplus so I am wondering whether they elected to use slightly different frequencies from those used by other parties. If I cannot find a suitable transmitter I may install another Receiver, such as used with Drones and move up to the 5.8GHz band The receiver module is in its own small diecast box and may be easily changed.

Thank you for your comments Ultrapurple 

Fraser

[Ultrapurple]

If it's UK Police surplus and operating above 2.50GHz then you will need to either retune it to somewhere 2.4-2.5GHz and use a suitable transmitter or, as you suggest, move to 5.6GHz. The 2.50-2.69GHz band has been re-allocated (sold) for mobile phone uses (at least in the UK).

The UK Frequency Allocation Table makes interesting bedtime reading.

[Fraser]

I just managed to purchase a used 1.394GHz 500mW Video Transmitter and Receiver set made by RDT Ltd  They cost me £30 for the pair, so very reasonable considering what they would have cost new  The predicted ‘line of sight’ range with the provided antennas is 750m to 1500m 
The units are quite compact with a case size of ~100mm x 60mm x 30mm.

I may use these to convert the ISG Monitor/Receiver to the dedicated licence exempt UK video transmission frequency that is centred on 1.394GHz with a 10MHz channel span. You do not see 1.394GHz video links much these days and hopefully the channel is quiet and should not interfere with my Wi-Fi network, unlike some 2.4GHz video transmitters.

Fraser

[Bill W]

1394 MHz is the frequency used for the Argus cameras analogue transmitters for the UK as well.  A few other countries also gave users licenses for it, despite their band plans.

Not just clearer of other ISM randoms but also better building penetration due to the lower frequency.

Bill

[Fraser]

Bill_W,

Yes indeed, 1394MHz is a useful licence exempt frequency. I feared that it had been removed from the licence exempt band plan as most references referred to the ISM bands where 1394MHz was not included. After some digging in the Ofcom document portal I found that 1394MHz is still alive and kicking      Not only is 1394MHz better at penetrating structures, the Ofcom regulations permit a transmitter output power of 500mW which is a ‘healthy’ amount amount of RF energy for longer distance links or “challenging” situations. My transmitter is capable of the full 500mW output, if such is required 

I have a 1394MHz colour video camera languishing somewhere in my lab. I shall have to dig it out. Time to look for some 1394GHz patch aerials or to make my own, as I have for 2.4GHz work.

Interestingly, 1394MHz is not legal for Air to Ground use in the UK. It is a ground to ground only frequency according to Ofcom. I presume this was an effort to control user to user interference with only the single 10MHz channel available.

I seem to recall that an old Amstrad analogue satellite TV box could be modified to receive the 1394MHz frequency allocation. The good old days when operating transmitters above 1GHz still seemed impressive 

Fraser

[Fraser]

I just had a look in my garage as I suspected I had some brand new professional RF video links...... annnnd I have 

I have six Genie CCTV waterproof 5.8GHz Transmitter plus Receiver sets, complete with whip antenna on the transmitter and patch antenna on the receiver    The electronics package is small and easily removed from the waterproof cases. The sytem is only 25mW transmitter power but at 5.8GHz and 7 channels, it will not interfere with my 2.4GHz Wi-Fi network

I now have a choice over which frequency band to use for my video link monitor 

Fraser

[Fraser]

Pictures of the Genie 5.8GHz video link set.

The receiver is fitted with an active (pre-amplified) patch aerial  That was a nice surprise.

[Vipitis]

This thread is becoming interesting again, as long as one can find these cheap, in working order and not too difficult to power.

[Ultrapurple]

It's worth bearing in mind that the 1394MHz allocation is too narrow for analogue colour - in fact, it's too narrow for full-bandwidth black & white 'PAL' video.

The rule of thumb for FM channel bandwidth requirement is peak deviation + (2 x highest modulating frequency)

So the 10MHz at 1394MHz is capable of supporting 3.5MHz video bandwidth with 3MHz peak deviation. (You can't reduce the deviation to, say, 1MHz and expect to get a decent picture, let alone increasing the video bandwidth to 4.5MHz; the maths is complex but take it from me...)

[Fraser]

Thanks Ultrapurple.

It will be interesting to see how the 1394MHz video link performs. Life is full of compromises so the 1394MHz video link is likely no different 

[Fraser]

It is interesting to see that Marrell still supply 1394MHz FM video link equipment to the broadcast and film industry. It would appear that these links are often used on Steadicam assemblies but I think they are only for the local monitors (video assist) so maybe video image quality is not so important ?

https://www.marell.co.uk/videolinks/list/

The prices are a bit scary at £900 each for the transmitter and receiver !