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Nov 10, 2019, 11:08 AM
JettPilot's Avatar
Quote:
Originally Posted by chileflora

So if I combine the two, I would be able to get a x3 - x4 distance range !!! =300+ km?! The only catch: I do not have even close an airframe to do such a feat, and then, to stay in line of sight, one would have to climb to 7000 m+.
Hi ChileFlora,

That would be amazing to fly a distance like that, you could fly all the way to Argentina, catch the mountain waves, and not have to drive

Have you ever tried 1.3 GHZ for video, I use it and like it a lot. 100 KM is pretty easy for 1.3 GHZ using a Yagi, and antenna aiming is not critical. With a good large GRID antenna on 1.3, I think you could get 300 KM petty easily.

Mike
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Nov 14, 2019, 06:58 PM
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Quote:
Originally Posted by JettPilot
Hi ChileFlora,

That would be amazing to fly a distance like that, you could fly all the way to Argentina, catch the mountain waves, and not have to drive

Have you ever tried 1.3 GHZ for video, I use it and like it a lot. 100 KM is pretty easy for 1.3 GHZ using a Yagi, and antenna aiming is not critical. With a good large GRID antenna on 1.3, I think you could get 300 KM petty easily.

Mike
I have never tried it, and this could have been my biggest mistake. Still, the videos which I have seen with 1.3 GHz did not really convince me. Most of them are pretty much worse than mine.

Now, as to Argentina, the aeronautical law says that you never should cross into foreign country. And I am law-abiding flier... However, on the other side of Andes there is a small town, about 70 km. from the border. So we could mount a first international FPV/RPA airline... My house would be the first international RPA airport, and some 170 km (110 miles) to the East someone would have to do the same in that town... He would need same groundstation as I do, and we would have to work out the protocol for control change from one station to the other right over border (you will quickly loose LOS after crossing border due to Andes).

I estimate that from west to east there could be flights about 5 days per week with acceptable weather, The other way round - only 2, maybe 3 (prevailing winds are from west)...
Last edited by chileflora; Nov 14, 2019 at 07:35 PM.
Nov 14, 2019, 07:04 PM
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As to 300 km video link... I think that I have it in my bag... on 5.8 GHz. There is a catch: on flatland, one would have to fly to 7000 meters to have barely clean line of sight.

Today I was doing some testing of my tracker, and used the 25 mW setting of the AKK transmitter. I uploaded a short video of the image quality on 25 mW, 27-29 km., 30 dBi dish. Last few seconds where the quality improves is when I switched to 200 mW.

25mW 28 km (1 min 51 sec)


To have this video quality, you have to point the antenna with a precision of +-1.0 ; going to 1.5 from the "sweet spot" began to produce very light snow, and going to 2.5 resulted in heavy snow on border of unflyable...

I also tried to switch to 21 dbi patch antenna at the same distance, but it was unfliable.

Now, some analysis of the experience:
I went as far as 32 km. on 25 mW, and my feeling was that one could easily go a couple of km. more, but I was really testing the lateral tracking of my tracker, so I was not very interested in that part.

Now, 25 mW at let us say 35 km mean:
if use 1.6 W (There is a 2W AKK!) = 280 km
There is a bigger dish which I can mount: a round one 90x90, around 32 dbi, and a 1,2 x 1,2 meters, 35 dBi (probably I still could mount it, but I would have to extend the legs, otherwise the tripod will tip over. The whole thing would weight around 45-50 kg.

32 dbi = 280 km-> 350 km
35 dBi = -> 500 km.

Now, I plan also to try out a directional patch yagi on the airplane, with 8-10 dbi.
So, if we go totally nuts, we would get:

2 W VTX, 1.2 m antenna, 8 dbi antenna on airplane = 900 km.

The bigger catch: the aicraft (or rocket, shuttle-style) would have to fly 60 km high to have LOS...

Now, instead of trying to get these extreme ranges, I plan to get crystal clear video at 100 km.
Last edited by chileflora; Nov 14, 2019 at 07:26 PM.
Nov 14, 2019, 08:19 PM
'Extreme Fabricator'
That is doubly impressive with a -85dbm receiver... no pun intended..
Have you considered an array Chileflora?
Another thing with bigger dishes is you can knock the focal point back which at the small expense of some gain, it will broaden your beam width while sustaining signal amplitude from the larger dish size. I once did an active focal dish utiling a linear actuator, you then have full gain (beam width control within a range.
Last edited by alicecooper; Nov 14, 2019 at 08:25 PM.
Nov 14, 2019, 09:24 PM
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The idea I have in the back of my mind is to install two dipoles as close as possible to the focus and transmit two channels from airplane (on different frequencies, obviously). The VTxs are nowdays extremely small and lightweight, so operating two at the same time is not such a big issue.

The other idea I had was to install several dipoles (with RXs) around the main dipole and take RSSI readings so as to have an instantaneous "picture" of where the best signal is. However, I am implementeing now a "swiping" algorythm where the antenna makes a movement to left,right,up, down (by about 2, but probably it will be automatically adjusted based on distance) and then determines the best spot. The whole process takes about 12 seconds.

I am still not convinced that RC305 are bad...

If you mean two dishes as array, I am 100% convinced that this is not good idea... And generally, making an array for 5.8 GHz is too tricky
Last edited by chileflora; Nov 14, 2019 at 09:44 PM.
Nov 14, 2019, 11:44 PM
'Extreme Fabricator'
In your application the RC305 seems to work fine but they are comparatively low on front end sensitivity compared to many newer options.
By array I mean a divergent array for real time position acquisition data, you are doing the same thing by moving your dish, but suffering time constraints. Using the one dish with the feed point movable would be another option.
Are you running a phase blocking plate with your current setup?
Nov 15, 2019, 12:00 AM
Are not men? We are DEVO! (7e)
xanuser's Avatar
Quote:
Originally Posted by alicecooper
You Want even more round?
These things were a bargain at just $35
Probably cost five grand originally.
yep those will work/ provided you don't dip below the curvature of the earth.
pick up a pair of those bad boys and you can prove any flat earther wrong in a (long) afternoon.
Nov 15, 2019, 02:17 AM
'Extreme Fabricator'
Quote:
Originally Posted by xanuser
yep those will work/ provided you don't dip below the curvature of the earth.
pick up a pair of those bad boys and you can prove any flat earther wrong in a (long) afternoon.
lmao... it still won't convince them, they will accuse me of tampering with the footage... The last hilarious crazy theory I heard from them was that jet planes are faking it, and always have been in that they don't actually use jet fuel, but instead run on compressed air... yep, throw the keys away on that one... a padded cell with plenty of medication is the only solution.
Nov 15, 2019, 11:01 AM
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Quote:
Originally Posted by alicecooper
In your application the RC305 seems to work fine but they are comparatively low on front end sensitivity compared to many newer options.
By array I mean a divergent array for real time position acquisition data, you are doing the same thing by moving your dish, but suffering time constraints. Using the one dish with the feed point movable would be another option.
Are you running a phase blocking plate with your current setup?
I am still working on the auto-pointing feature, from the limited experience I had so far: if the tracker is good (like mine seems to be), you have to use auto-pointing maybe once or twice during a long light (2-3 hours). Now, since the tracker relies on GPS data received from plane, if this link goes down (happened a couple of times during last test flight, I am working out now if it is some problem with DL modem or with my program), there will be no tracking, obviously. One idea would to use this auto tracking to continuosly track the airplane without GPS downlink. It would work like this:
tracker does autopointing, leaves the antenna at the best spot, and takes note of the RSSI value.
Once RSSI drops by about 10 %, the tracker repeats the process.
At longer ranges this would prevent constant chasing, while providing relatively good tracking at medium ranges (5-20 km) with lateral flight.
If I determine that GPS downlink is stable enough, I would say that array-type trcking with 4 dipoles and 4 RXs is really overkill.

The other idea is that one could develop an antenna head with 4 elements for pointing, and one main RX. There are plently cheap Rxs (nonRC305) with RSSI, so that one could make this as an independent unit which could be fitted to any dish, be it 40 x 40 cm or cosmic 2 meter. For the main Rx I would insist on using RC305 for the time being, but they are not extremely cheap, about 50 USD. Now, with a small arduino nano as the mastermind, one would get a perfect universal tracker.

One issue one must be careful about are the side lobes of the antenna, which can fool the autotracker (and a couple of years ago they fooled me and almost brought down my plane)...
Last edited by chileflora; Nov 15, 2019 at 11:10 AM.
Nov 17, 2019, 09:01 AM
'Extreme Fabricator'
Just thinking outside the square, and putting the idea to you just for the sake of some idea's, but you could also set the antenna module on a variable circular orbiting mount with a simple position feedback system. That orbit would effectively scan a variable conical circular pattern in the sky without changing polarisation or dish position. With an RSSI feedback error loop you could automatically vary the radius of the orbit to change the cone angle as required to maintain a minimal RSSI amplitude differential. The position feedback with RSSI data would also give you an exact azimuth to target to control dish position servo's.
The RSSI differential amplitude is used to generate the diameter of the orbit, keeping it to less than 30% of peak value so you never actually lose signal, the dish can simply follow the direction it's told on both axis to maintain the lock to within about 30%. The orbit direction clocked with RSSI peaking gives a direction value for the dish position correction. The further out you get, the smaller the feed point orbit will get until it remains stationary, but the dish will also remain locked until the target moves. It's error corrected status will always strive to orbit the feed point down onto target. If the target moves out of the now uniform orbit, the direction is immediately known and is corrected by dish movement.
It has been done in some other non civilian applications, so it's mostly just down to engineering the servomechanisms and crunching some basic data.
(Just don't tell DARPA where you got the idea... lol)
Nov 17, 2019, 11:23 AM
Registered User
Quote:
Originally Posted by alicecooper
In your application the RC305 seems to work fine but they are comparatively low on front end sensitivity compared to many newer options.
...
Why don't you demonstrate these newer options marketing BS is true with a real flight exceeding those posted by RC305 users ?
Nov 17, 2019, 07:14 PM
'Extreme Fabricator'
Quote:
Originally Posted by renatoa
Why don't you demonstrate these newer options marketing BS is true with a real flight exceeding those posted by RC305 users ?
I don't need to...
I have no commercial interest in any of them.
I do have some RC305's and they still get occasional use, but even with the same antenna's I cannot reach the end of my valley, about 6km away running the same planes, yet they will easily do double that range with some other receivers I've mentioned.
Another small detail I recall from those 305 days (around 2014) was the Skyly modules used had claimed sensitivity of -85dBm... they were originally created for consumer market video senders with intended limited range, and by intended it was to prevent interference from other video senders in high urban density environments.

If I have RC305's and don't use them, it's only because I have far better performing options. So why inform anyone of that, especially on forums about long range?
Seems it's better to just keep quiet about it.
Nov 21, 2019, 07:56 PM
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Thread OP
Today I was finally flying with autotracking by RSSI. I have two buttons, one for vertical scan, the other for horizontal, the system moves the antenna to the left or down by a few degrees, then slowly scans to the right or up at a speed of 1/second. The scan is:
for horizontal: +-2 or 4 (depending in sensitivity set by another switch)
for vertical: +-3 or 5

It averages 30 readings per 0.1 or 0.1 seconds. Probably one could double the scanning speed. Now, the whole scan takes between 6 and 12 seconds, but the scan does not virtually affect the visual "experience".

Small red dot on the graphs is the center, i.e. the original direction of the antenna.

The system calculates by how much (in degrees) one would have to move the antenna for the best RSSI value. Once adjusted for the best reception, the pointing does not change by more than 0.5 - 0.7 degrees.
Last edited by chileflora; Nov 21, 2019 at 08:03 PM.


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