HowTo: Many FPV Pilots Simultaneously

[RobanyBigjobz 0]

 

Interesting video from Alex Greve on how to get many FPV pilots flying together. Just as importantly for a nosey devil like me, is it includes some info on how it works too. N.B. I have not checked the UK legality of all the frequencies they claim to use. Let's call that an exercise for the reader?

 

 

 

 

[Bravedan 106]

 

Strange accents, must come from north of Watford......................... couldn't possibly be from a completely different country with completely different standards and rules, could they? After all, that would mislead, wouldn't it.................

 

1. For UK legality, one band of eight has to be completely discounted.

2. For UK legality, HALF the "Race Band" has to be discounted.

3. Then there are cross band frequencies that are far too closely spaced for simultaneous use with available and affordable equipment, certainly not what any UK hobbyist is likely to own. Example? 5733, 5740 and 5745, for a start. 5 MHz separation on analogue transmission from small lightweight low power equipment?

 

I also seriously question their claims with regard LHCP and RHCP separation being the Holy Grail to 5.8Ghz heaven, but have not specifically tested two Tx's operating in that orientation. What I HAVE done is deliberately mismatched a RHCP Tx to a LHCP Rx, and while visible signal loss was evident, it critically was relatively small, not enough to prevent a picture that was intelligible. If signal loss is demonstrably that small, as I found on more than one Tx/Rx make, crosstalk is a problem and it remained evident on adjacent channels even at 20MHz spacing, so must be an issue must it not?

 

The bottom line is that many people entering FPV are buying what sellers are selling, and even a lot of major UK based sellers are selling low quality and illegal (in both frequency and power) equipment.

 

I tested one UK FPV specialist supplier, pretending to be new and so not to know, and requested they select for me a UK suitable VTX/VRX pair. The VTX they selected had NO UK legal frequencies, and was 200mW fixed when the UK max is 25mW. When challenged they said, and I do quote "I suppose you do want to see further than your elbow, don't you".

 

It's a jungle out there...................difficult to see clearly............

 

[RobanyBigjobz 0]

 

I was posting this more for the engineering/physics demonstration of what's possible because they actually achieved it. I'm sure it didn't escape your notice that there was an explicit rider about not claiming if this would be legal in the UK I sympathise with your view that vendors are pretty useless about what's legal and what's not, but that wasn't the focus of the post.

 

One of the more interesting bits of the video for me was the section on axial ratio and the need for it to be high enough for what they suggest to work. For anyone who hasn't watched it, all CP antennas emit/receive both LHCP and RHCP and axial ratio is a measure of how dominant one mode is over the other.

 

These definitely-not-Watford types said that high axial ratio of all antennas is required to have LHCP and RHCP working ok at nearby frequencies. The three and four-lobe cloverleaf antennas that are very common have quite poor axial ratios so they don't reject opposite polarisation well. Patch antennas didn't do especially well either. I think all yours were of those two designs, Dave, please correct me if my memory is wrong Your test observations would seem to prove their point that poor axial ratio antennas are no good for close channel work, no? They also suggested tying the audio channel to ground to cut the bandwidth and thus the amount of cross-talk between nearby channels.

 

Perhaps the techniques they show could be adapted for UK FPV to get more friends flying at once, legally?