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Mar 18, 2017, 04:25 PM
Registered User
Question

25mw Transmitter Range


There re a lot of output power ranges on FPV transmitters. Some are real low. I saw several; at 25 mw,

What kind of range can you get at 25 mw is my question? I need a rock solid one mile range. So, any ideas on what it takes to do that?
Last edited by drpropman; Mar 21, 2017 at 10:04 PM.
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Mar 18, 2017, 07:02 PM
fly by night
BCSaltchucker's Avatar
think control-line distance
Mar 19, 2017, 02:07 AM
Registered User
Quote:
Originally Posted by BCSaltchucker
think control-line distance
Autonomous doesn't care about that. So, how far can 25 mw's get you these days?
Mar 19, 2017, 04:08 AM
Registered User
PilotsSummer's Avatar
I've an adjustable VTx - 25mW, 200mW or 600mW.
Of course I only use the 25mW setting because thats the limit for 5.8GHz in the UK..

Anyway, 25mW gives you ok results out to say 200m. Poor results from 200m to 300m. Signal fades away altogether at about 400m. All approx distances obviously.

So, yes, 25mW is extremely limited and does not support FPV flying within the UK legal LOS flying range (of about 500m). A more reasonable UK legal power limit would have been 200mW (but UK law is not about "reasonable"!).
Mar 19, 2017, 04:18 AM
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PilotsSummer's Avatar
I think "...a rock solid one mile range.." would need 600mW at 5.8GHz.

I've seen (others!) get to 2km with standard 5.8GHz video equipment and 2.4GHz control gear (L9R control receiver) using a 600mW Video Tx.

1 mile = 1.6km
Mar 19, 2017, 05:41 AM
Registered User
from what i have seen most usa folks get there ham licence and use 1.2/1.3 rather than 5.8.in uk can only use 5.8 for fpv as ham licence is only for radio with 25mw system you have to use antenna tracker and high gain antennas
Mar 19, 2017, 12:02 PM
Registered User
Quote:
Originally Posted by sweets
from what i have seen most usa folks get there ham licence and use 1.2/1.3 rather than 5.8.in uk can only use 5.8 for fpv as ham licence is only for radio with 25mw system you have to use antenna tracker and high gain antennas
I feel for you guys. UK law is as stupid as much of the law in America post 911. In the ham radio world, the rule of power is 1 watt = 1 mile. That seems to fit with FPV as well. 25mw is crazy! I will find something in the 1 to 2 watt power range based upon whats been aid here so far. I only want to reach out a mile, but I don't want to be on the edge of LOS at that point. Do you ever get the feeling that our masters wish FPV was never created?
Mar 19, 2017, 12:52 PM
Registered User
PilotsSummer's Avatar
Thanks for the sympathy!

The low power limits will be to avoid stepping on the toes of business people who use the same 5.8GHz bandwidth for monitoring fish farms, warehouses and the like.

In general the new FPV laws are a lot more about commercial pressures than they are about safety. Big global companies have long-term plans for the first few hundred feet of airspace and want to push hobbyists out of their way - so they lean on the lawmakers to get what they want. I really think its as simple as that.

We have the UK "Drone Code" which is more than enough for safety.
Mar 19, 2017, 03:47 PM
fly by night
BCSaltchucker's Avatar
how would they know you're not using 25mW if you use a switchable vTx (25/200/600)?

also, 25mW does not have a fixed/absolute range. A very well tuned set of antennas on 25mW power could achieve better range than 600mW with average antennas. Key is, you have to have the equipment and the advanced skills to know how to tune antennas. And also consider diversity with at least one really high quality directional antenna.

highly skilled hobbyists like IBCrazy have achieved impressive range on low power vTx by applying their tuning skills, using an SWR meter. Though I agree, it is so much easier to just go to lower frequency like 1.2/13.GHz and instantly have massively improved penetration and range - IF you test the equipment and use only equipment which has good sensitivity and reliability. Might want to contact IBCrazy for more info on how to get the most range from 5.8 these days.
Last edited by BCSaltchucker; Mar 19, 2017 at 03:56 PM.
Mar 19, 2017, 04:16 PM
Trith_FPV
TR1T0N's Avatar
I have a 200mw and 400mw ( ordered a 600mw today ) but I have gone up 3000ft, and out about 500m. That was on 400mw with 2 Triumph Antenna. I still had perfect clarity.. but my Rx was getting sketchy. So I brought it back!

I bet 400mw with a couple Triumphs could hit 1mile+ if you didn't have any obstacles in the way.
Last edited by TR1T0N; Mar 19, 2017 at 04:17 PM. Reason: 5.8Ghz of course
Mar 19, 2017, 04:52 PM
Registered User
PilotsSummer's Avatar
I think its unlikely someone using more than 25mW 5.8GHz would get noticed.

Yes, you can get more range using high gain aerials. Yes, you would need to point the receiving aerial directly at the aircraft at all times - painful to do manually; more expense/complexity to do automatically (using tracking). I would need convincing you could ever get great results in practice if you are stuck with a very low power signal and a rapidly changing angle between aircraft and ground station.

Yes, diversity helps. I use a CP aerial for very close and a low gain patch aerial for further out. And diversity is less bother than tracking.
Mar 20, 2017, 12:49 AM
fly by night
BCSaltchucker's Avatar
Quote:
Originally Posted by TR1T0N
I have a 200mw and 400mw ( ordered a 600mw today ) but I have gone up 3000ft, and out about 500m. That was on 400mw with 2 Triumph Antenna. I still had perfect clarity.. but my Rx was getting sketchy. So I brought it back!

I bet 400mw with a couple Triumphs could hit 1mile+ if you didn't have any obstacles in the way.
last time I checked the 5.8 long range flight record was .. 38km range using a 200mW vtx, and a finely tuned helical on receiver
Mar 20, 2017, 03:05 PM
Trith_FPV
TR1T0N's Avatar
The OP did not specify his platform. Rather then not replying .. Im supplying my experience. Which is FPV micro quadcopters. I also stated that using Triumph antenna, what he could expect.

Maybe OP could be more specific as to his platform and setup?
Mar 21, 2017, 08:19 AM
FPV guru
evensis's Avatar
Quote:
Originally Posted by drpropman
I feel for you guys. UK law is as stupid as much of the law in America post 911. In the ham radio world, the rule of power is 1 watt = 1 mile. That seems to fit with FPV as well. 25mw is crazy! I will find something in the 1 to 2 watt power range based upon whats been aid here so far. I only want to reach out a mile, but I don't want to be on the edge of LOS at that point. Do you ever get the feeling that our masters wish FPV was never created?
You can do 2km with a pair of cloverleafs tx/rx on 200mw which will achieve your 1 mile range, although wouldn't call it 'rock solid' at 2km and weather has to be on your side. If you're insistent on 25mw, you're going to need ~ 10 turn helical on the rx to achieve it (or anything with > 12dbi gain). Plus the added fun of keeping your model in the beam width of the antenna. 400/600mw will comfortably get you where you want to go with a pair of Aomway Cloverleaf cheapies.

Quote:
Originally Posted by BCSaltchucker
last time I checked the 5.8 long range flight record was .. 38km range using a 200mW vtx, and a finely tuned helical on receiver
The helical was on the focal point of a parabolic dish if memory serves me right.
Last edited by evensis; Mar 21, 2017 at 08:44 AM.
Mar 21, 2017, 10:01 PM
Registered User
Platform: A homemade tricopter on a wood frame.

I fly short range line of sight, but FPV videos are just wild. I gotta give it a go.

I'm a radio man. I make ARRL antennas using the handbook. So I can tune, but I want to make sure that I don't have a sudden signal loss at the range edge so power and knowledge are essential. That's why I asked the question.