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Aug 23, 2016, 08:53 AM
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ghostwhiper's Avatar
Quote:
Originally Posted by flipflap
it shouldn't normally destroy the transmitter.
I disagree, not shure if you can remember this post.
https://www.rcgroups.com/forums/show...0#post32926989
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Aug 23, 2016, 09:06 AM
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Thread OP
That's a completely broken antenna, equivalent to no antenna at all. I agree that this can damage the transmitter as it will have the worse SWR possible.

I've updated the first page about the risk :

Quote:
Antennas
Be careful that this system is powerful and requires good antennas. The monopole antennas (such as provided with the OrangeRX and Wolfbox modules) won’t give good results and can sometimes damage the modules. Have a look at this page for antennas recommandations.
For testing purposes I recommend to use dummy load to avoid all risk and interferences.
Aug 23, 2016, 09:10 AM
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ghostwhiper's Avatar
Quote:
Originally Posted by flipflap
That's a completely broken antenna.
All my antennas where broken like that!!
Aug 23, 2016, 09:45 AM
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Thread OP
Quote:
Originally Posted by d3nys
What's the relationship with the rssi % seen in the OSD vs dbm. Thanks.
I thought I had already put a more complex formula but realize it's still very simple :

0% = -100 dBm or below
10% = -90 dBm
20% = -80 dBm
30% = -70 dBm
40% = -60 dBm
50% = -50 dBm
60% = -40 dBm
70% = -30 dBm
80% = -20 dBm
90% = -10 dBm
100% = 0 dBm or above

* So the issue is that when the plane goes away the signal drops quickly to let's say 30% and then go down very slowly, which is perfectly normal because the relationship between RSSI in dBm and distance is not linear. Notice that this is pessimistic, as for example wifi will show 100% as soon as the signal is above -50 dBm, while here we would just show 50%. So many users will wonder if it's normal to have a low RSSI at a low range, but yes, that's only the way the RSSI is represented.

* This scale wasn't used since the beginning, now at 0% we're very close to the limit (we still have about 2 dBm margin). So it's difficult to compare to old results without first translating in dBm.

* For all the values 0-100% RSSI there should be no packet loss. Packets will start to be lost around -102 dBm. That's why some other systems such as openlrsng do represent the RSSI in a different way : between 50% and 100% it's really the RSSI, and between 0% and 50% it represents the rate of packets lost. So again the RSSI shown in ULRS is very pessimist, that's why I'll probably change the formula to preserve the users nerves.

I've updated the page on the site to reflect this :
http://www.itluxembourg.lu/site/ultimate-lrs-rssi/
Last edited by flipflap; Aug 23, 2016 at 09:51 AM.
Aug 23, 2016, 09:47 AM
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Thread OP
Quote:
Originally Posted by ghostwhiper
All my antennas where broken like that!!
I was more lucky and had some good duckies, but not all.
Aug 23, 2016, 10:41 AM
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ghostwhiper's Avatar
Quote:
Originally Posted by flipflap
I thought I had already put a more complex formula
Depends a whole lot if you use high gain antennas i guess.
In that case it doesn't drop in a linear line, with the way you formulate it.

With the +8db gain (theory) yagi for TX and +2.8db gain (theory) dipole i used for testing i had a full 100% rssi up to 3.5km, after that it dropped to 75% up to 5km and then dropped again to 70% at 10.
Thats not a linear line for RSSI @ distance A would be a theoretical RSSI @ distance B.
If i am correct that also means that the list you have posted could be flawed regarding the rssi vs db loss.
Going to ask another HAM about this to confirm or correct that for me.

One things for shure, i am going to do some testing again within a couple of weeks.
Going to use a 8db yagi on a tracker at 4 meters above ground level, 2.8db dipole on the still to be ordered plane,

Going to plot distance to home, rssi from the apm and TX db from ulrscc.
For good measure i am also going to use a moxon tx and dipole rx
Monopole tx and dipole rx.
Yagi tx monopole rx
Moxon tx monopole rx
Monopole tx and monopole rx

All flown on the same auto mission of 5-10km

Should give some solid results
Aug 23, 2016, 11:29 AM
Registered User
Replaying my DVR and looking at the estimation spreadsheet it gives me consistent numbers at different locations of max distance 600-700km. I have a yagi and a forward facing V antenna both tested with good SWR. Incredible.
Aug 23, 2016, 11:56 AM
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Thread OP
You perfectly right, as I am : there's a misunderstanding as the percentage is not a percentage of the maximum range, it's a percentage of the analog RSSI display. I should just have expressed it as a voltage to avoid any confusion :

So 0% = 0V and 100% = 3.3V

What's linear is the relationship between the RSSI in dBm, and the value shown on the RSSI analog display. That's practical because if it has 10 or 100 marks you can immediately read the RSSI value in dBm.

And you're right that the distance isn't proportionnal to the RSSI value (or displayed value).

It's even very non-linear : it will drop very fast at the beginning, and then very slowly.

For a user who has antennas able to go to 30 km, if we check the ULRS range estimator, we see that at 10 km he will have a RSSI of -92 dBm (=8% on the analog RSSI display). So he might think he's close to the limit, but he's only at one-third of the limit.

And your case is special because you're a ham with an incredible antenna on a mast, and so at 5 km you've got 75% RSSI (=-25 dBm). But like for other users, the RSSI is very non-linear with distance : at 10 km you've lost only 5% RSSI at 70% (=-30 dBm).

Notice that this is perfectly normal according to the theory : the relationship between RSSI and distance is that when the distance is doubled the RSSI is reduced by 6 dBm. OK here it's only reduced by 5 dBm, but we agree that reading an analog meter to 1% accuracy is difficult.

Now let's check your maximum range : with 70% (=-30 dBm) at 10 km, you can achieve 398 km maximum. Of course if the plane is high enough to be in line-of-sight.

And even if you yagi is excellent, there are yagis with higher gains so it's possible to reach even higher distances.

It may seem a lot, but remember a user (I think it was srnet) who made an experimental satellite, which orbits at something like 1000 km, equipped with a RFM23BP and dipole, and he can listen to it with a relatively cheap portable antenna and radio scanner.
Aug 23, 2016, 12:02 PM
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Thread OP
Quote:
Originally Posted by d3nys
Replaying my DVR and looking at the estimation spreadsheet it gives me consistent numbers at different locations of max distance 600-700km. I have a yagi and a forward facing V antenna both tested with good SWR. Incredible.
That's a very powerful system, with good antennas that's a possible range, but only in line-of-sight.

Other examples of comparable systems is the record for PMR radios, of 535 km with 500 mW (or 1W ?) : https://en.wikipedia.org/wiki/PMR446
Aug 23, 2016, 12:20 PM
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Hello All,

I have made some successful test: Ground to ground tests estimated 27.5km, tested in real 24km.

I have been doing some range test on ground and on air. Our target is MAVLINK working so we don't test if it have control (move servos or so), we check than we can upload a mission of 20 waypoints.

I use real distance and attenuators to test in short distances and extrapolate results. To test range with attenuators is very interesting because it is very easy and you can make tests quickly. We use to use the 30dBm attenuator

6db is 1/2 the range
12db is 1/4 the range
18db is 1/8 the range
24db is 1/16 the range
30db is 1/32 the range

Results: both using a yagi with 3 elements and a dipone on RX

ULRS
Ground to ground (some month ago)
23.9km - Arming motors form Tower (Pixhawk android software)

Ground to air with 30dB attenuator (Today)
860m (estimated 27.5km without attenuator)

It can be improved because we are using wolfbox than get about 0.3W and we have not optimized antennas (diy antennas with not measurement equipment)

So i think 40km with full telemetry support is possible.

Very diferent than test made with TBS Crossfire!!!

TBS CrossFire:
Ground to ground (with 30dB attenuator) and standard dipoles
30m!!! (900m without attenuator)
Aug 23, 2016, 12:25 PM
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Dancy's Avatar
Quote:
Originally Posted by flipflap

And you're right that the distance isn't proportionnal to the RSSI value (or displayed value).

It's even very non-linear : it will drop very fast at the beginning, and then very slowly.
We used to call this the "Inverse square law" in radar school. "Each time you double the distance the power will be 1/4"

Example: 1 watt at 10 meters will be 1/4 watt at 20 meters

Dan
Aug 23, 2016, 12:34 PM
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Dancy's Avatar
Quote:
Originally Posted by flipflap
It could be tested from a real plane, or a paramotor, but I've seen several users doing more than 100 km with common frames such as X-8.
!?!?!?!?!

Do you mean an Octo-copter? How is this done? I have not done a great deal of testing but just off the top of my head, an Octo-copter might reach speeds of 80 kph. Out and back to 100 km would require a flight time of over two hours. I have been able to squeeze 20 minutes out of one of my blade/motor/battery combinations but I would love to learn how to get over two hours out of a system.

Dan
Aug 23, 2016, 12:39 PM
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Dancy's Avatar
Quote:
Originally Posted by samisin
Just tested my advanced power management design !!
Guess what it works like a charm!!
plug all power sources no problem the one with higher priority will be the only current path!!
no shottky diode leakage!!
way much less voltage drop on p channel mosfets
I will do tx version of the board after testing Jr version of the design.
I will finish the routing tomorrow and will send it to oshpark this week. I already bought BT modules . 10 of them for 30$
What? Have you been taking time to eat and sleep? (tease!)
Aug 23, 2016, 12:45 PM
Registered User
x8 is a big flying wing
Quote:
Originally Posted by Dancy
!?!?!?!?!

Do you mean an Octo-copter? How is this done? I have not done a great deal of testing but just off the top of my head, an Octo-copter might reach speeds of 80 kph. Out and back to 100 km would require a flight time of over two hours. I have been able to squeeze 20 minutes out of one of my blade/motor/battery combinations but I would love to learn how to get over two hours out of a system.

Dan
Aug 23, 2016, 01:32 PM
Registered User
Thread OP
Quote:
Originally Posted by Dancy
!?!?!?!?!

Do you mean an Octo-copter? How is this done? I have not done a great deal of testing but just off the top of my head, an Octo-copter might reach speeds of 80 kph. Out and back to 100 km would require a flight time of over two hours. I have been able to squeeze 20 minutes out of one of my blade/motor/battery combinations but I would love to learn how to get over two hours out of a system.

Dan
Skywalker X8 is a flying wing, here in a 155 km flight. I didn't say 100 km out and back, just 100 km out and someone to get it there

X8 wing endurance test. Total flight path 155km! (2 hr 50 min 40 sec)


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