RC Model Reviews

Hi Bruce,

We had problems a few weeks ago when a few of us met up to fly together. Three of us had the 200mw 5.8ghz Hobby King kit and we found that, no matter what channels we all selected, if one of us turned on our plane on the ground, it wiped out the signal from any planes up in the air. It was understandable, since we were all within about 20m of each other on the ground while the planes were 100's of meters away in the air (scary stuff if you were the guy in the air), but I wonder if you could address this in your FPV videos. Is there better quality receivers, or transmitters, that will be more exact about the frequencies? Should we have all stood 50m apart (can't really chat then)? Any other ideas? As it was we just took turns in flying, but really the point was to be able to get up in the air together.


Eddie

PS, Will your video backpack have channel selection? Also, please add audio to it, being able to hear your motor is very handy.

I was curious about this also...
If others are flying on 5.8 would the backpack setup interfere?
At the local club the 5.8 guys have a board and must request a specific channel..would the FPV have need its own channel.

The Foxtech 5.8GHz system (ie: not the Immersion one) has very wide channel spacing so I'm surprised to hear that you had an issue.

The spacing of the ground-stations has no real effect -- since they are passive and shouldn't interfere with each other.

I'll do some experimentation -- which is very important because I have a project coming up that uses two 5.8GHz channels at the same time

(3D FPV? Who said that? 3D video visor? What? eh?)

It wasn't the ground stations being next to each other as such. Just that we generally turned our planes on next to our ground stations. Please do test it, because it completely overrode the more distant, but correct channel, signal. It was like we were all on the same channel, but we even downloaded the channel setting diagram while we were there to make 100% sure we were on different ones. It probably doesn't matter but we were on channels 1, 5 & 8.

The receivers are not exactly designed to cope with strong signals on adjacent channels so it will be interesting to do some tests.

There are very good ways to improve the situation though -- for example, if you have to users operating with opposite circular polarization that will make a huge difference -- the revers polarization effectively weakening the strength unwanted frequency by a factor of 100.

RCModelReviews wrote:the revers polarization effectively weakening the strength unwanted frequency by a factor of 100.

???
where do you get that number from? the worst case crosspol of the fairly common cloverleaf antennas is about -9dB so a linear factor if rougly 10

RCModelReviews wrote:if you have to users operating with opposite circular polarization that will make a huge difference -- the revers polarization effectively weakening the strength unwanted frequency by a factor of 100.

Good thinking Bruce. I've been meaning to make some more exact-spec antennas, I'll make reversed ones.
Shotglass, I believe rp cloverleaf antennas cut the signal by -27db.

Edit: it appears I was wrong with -27db, although I'm sure I read that somewhere.

After searching I found -9 to -20db with an average of -15db.

not sure where you got that -27 from since from the graph it looks like the peak xpol is about 35db (bit hard to tell since he doesnt have a rhcp gain plot in that post although at >30db xpol plotting abs gain instead of the rhcp gain hardly makes any difference)
at least at theta 110

RCModelReviews wrote:The receivers are not exactly designed to cope with strong signals on adjacent channels so it will be interesting to do some tests.

There are very good ways to improve the situation though -- for example, if you have to users operating with opposite circular polarization that will make a huge difference -- the reverse polarization effectively weakening the strength of the unwanted frequency by a factor of 100.

Let me show my ignorance and ask:
If the aerial is inverted will the polarisation field reverse? Is the polarisation more subtle than that, or could you loose signal when flying inverted?
Also could the cloverleaf aerial give a range increase on the 2.4 GHz RC link if the former is not the case?

BillGriffiths100 wrote:If the aerial is inverted will the polarisation field reverse?

no

could you loose signal when flying inverted?

not because of polarization at least
unless your plane has a rollrate of about 12billion rolls a second you wont need to worry

Also could the cloverleaf aerial give a range increase on the 2.4 GHz RC link if the former is not the case?

possibly but not really a significant one