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Terry

My 4way Diversity Receiver

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Well it was not intended as 4 way diversity as such, just 4 way auto switching. The idea was to move on from the auto tracking aerial I have been using as it can loose track at close range. Now that receiver modules are cheap I felt it was time to give it a go. I will return to the auto tracking aerial idea but only with a much higher gain aerial than I have been using and maybe a new way of auto tracking. Anyway this 4 way receiver works well with the added bonus of diversity. I have tested it round the house using a 10mW transmitter in my hand as I walk from room to room. The picture never breaks up but I do get thin lines across the picture all the time as it always seems to be switching between receivers, this is not a problem for me but may not be good for you if you need perfect video. I have just come back from my first propper test with my slowstick and a 10mW transmitter in the local field. Results were good as far as it goes but I was using my Eye-Trek glasses for the first time and they were not so good. I had problems seeing the picture due to the low sun an I had to turn up the brightness to full. As far as I could see there were no thin lines this time but it was hard to tell. I flew 1/4 mile max with only a few short drops maybe due to some network interference I noticed a one point. Anyway my conclusion is that it out performs my autotracking aerial by a long way, it will be good to test it with my TwinStar when the weather and time permit.

post-6-1166275871_thumb.jpg

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Nice work Terry, put a video to see the perfomance of it. I´m a step behind trying the autotracking antenna. Are those Patch circularly polarized??.

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Thanks Wavess,

I would love to record a flight but the only recorder I have is VHS and I can only just carry the gear I have now as I am on foot. Maybe when I get to do a propper long range test with the TwinStar I can do it as I will have the car.

The patches are not circularly polarized Im sad to say, I made them intending them to be but they are linear. So far it has not shown to be a problem probably because I keep my turns gentle. If anyone has plans of a proven circularly polarized patch I would be interested to try it. I was told that they would have less gain than linear patches though, can anyone confirm ?

Terry

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Good job! Did you ever figure out why one your Airwave rx's seemed to have low sensitivity?

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Thanks Wavess,

I would love to record a flight but the only recorder I have is VHS and I can only just carry the gear I have now as I am on foot. Maybe when I get to do a propper long range test with the TwinStar I can do it as I will have the car.

The patches are not circularly polarized Im sad to say, I made them intending them to be but they are linear. So far it has not shown to be a problem probably because I keep my turns gentle. If anyone has plans of a proven circularly polarized patch I would be interested to try it. I was told that they would have less gain than linear patches though, can anyone confirm ?

Terry

Have you seen this site?

Circularly Polarized Patch

I´ve tried this one:

CP Patch

but for me it´s not circularly polarized,almost every position of the tunning coin tried without success. The Patch works great but it´s linear.

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Others (cyber-flyer, me, and one other fellow) have tried the circular polarized patch antenna from the ultimatecharger site. Same as you -- it tested as a linear design.

Frankly, getting circular polarization is VERY difficult. The designs that work well usually employ complicated construction. I even found that some commercially advertised "circular" patches are not that at all.

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Mr RC-CAM, I have a confession to make. When I first finnished the receiver I connected it to the same PSU as my LCD screen and when I connected the video cable it blew all 4 modules. I forgot the LM6574 was working on a +5v,0v,-5v supply and because of the way I made it by connecting the video lead I fed 12v into all the modules :( Its got its own battery now :)

Wavess, that is the site I based my design on, and mine too works great but linear.

Terry

Edited by Terry

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That really was a shame. Was the module's high voltage the reason for the low Rx sensitivity issue you mentioned, or did it just act as the final nail in the coffin? Do your new modules all appear to have the exact same performance?

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No everything was working ok until I connected it to the same battery as the LCD screen.

The new modules seem much better matched, I cant tell them apart so maybe it was not all bad.

Terry

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Thanks for posting your results Terry. It helps to know what works.

I agree on CP - it's tough to find one that actually works.

I wonder if the ceramic patch antennas used on GPS receivers are true CP. The manufacturers said they are, but I have my doubts.

I also observed sensitivity variation in Airwave RX modules. And it happened in front of me - that is one module that was good yesterday, became bad today.

My theory was that their front stage design is suseptible to static electricity and it gets blown by merely touching anntena connected to it. I don't have good proof of it but I do have couple of bad Airwave RX modules lying around - so I have to have some explanation. :)

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Yes it maybe static that dose it but I have found that the push on cases of the sardine can give odd results if they dont make good contact in the right places. Im not sure how bad it can get but I have noted some odd paterns on the screen under low signal conditions that go away if you squeeze the covers. When I took off the covers I noted some black dots where the contact areas were that indicate current flow so I drilled these points and soldered the covers. The problem was gone but I dont know if this is the whole answer as I have not done propper testing. Can anyone else add anything to this ?

Terry

Edited by Terry

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With regards to the tin sardine can covers, I recommend that they get soldered to the chassies at the corners. This can help reduce vibration induced noise. This fix is also good for the other Video Tx's that have friction fitted metal covers.

Just don't go nuts with the solder. One day you might want to open up the case.

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I flew twice yesterday but on both flights suffered a lot of interference. On the first flight I got wireless broardband lines and on the second I got a ghostly face appear at odd times from a TV sender. I was surprised as I was 300m away from the closest houses. I'm thinking I may be forced to use a bit more power or point the aerial directly at the plane when I'm close to houses.

I did record the flights on VHS which play ok directly but they are unwatchable after being transfered to my pc and even worse after making in into a DVD.

Terry

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Thought it was time for an update. I have been using the 4 way system for the whole Summer and I'm glad to say it's been great !

It takes a lot of the fuss out of flying FPV, no need for a helper, no worry about them pointing the aerial at the plane properly. My main worry was that there would be reduced range when the plane is between 2 patches but this has not shown to be a problem. I guess the very wide beam of these patches covers the join quite well. At the odd times video is lost I now just wait for it to return rather than panic about my helper not pointing correctly (less swearing) as I know it will return. One flight I was at 1500ft directly over the aerials and as you may expect the video dropped, I just waited (15sec) until the plane was caught by one of the patches then continued flying as I knew the plane must pass in front of a patch on it's way to the ground !

All flights have been made with a 100mW transmitter and I have flown out to just over 1 mile so the Airwave modules have been ok. Having said that 4 Way Mark 2 is on its way and I am using more sensitive receivers. Also I am using shop bought 8.5dbi patches, not because mine were no good but they are easy to damage in transport and these were cheap.

Here is a look at the head unit, video switching will be in a separate unit.

post-6-1190831302_thumb.jpg

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That's a great looking affair. The hardline coax gives it a nice industrial look too.

How about a fifth Rx for overhead? :)

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I thought long and hard about one overhead but it would have to be circular. In the end I decided it was not needed as flight under 1000ft is not a problem with the mk1 unit unless the plane is dead overhead and then I think it is more of a problem with the TX aerial so very high level flights will be done using a different system. This is my prefered system for general flights up to 1.5 miles. Once 1/2 mile out it will work up to 1500ft and I guess much more but I have not been over 1500ft yet.

My best aerial for overhead work is my helical but I try to avoid needing to be directly overhead.

There is another system I am working on but I have not received the parts yet. All I will say for now is the parts are 16dbi patches ;)

Terry

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Terry ... sweet looking RX! I too noticed the logical hard coax! So are you teasing us now with the 16db thing? C'mon tell us :lol: What's up your sleeve now? Wait...don't tell me it's a Ace of Spade right? ;)

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So are you teasing us now with the 16db thing?

Yes :D

What's up your sleeve now? Wait...don't tell me it's a Ace of Spade right?

Not quite, my Ace would be to get away from 2.4Ghz but I am working on an automatic long range system. I can't share too many details as I have about 3 systems in mind and I don't have a clue at this point which one I will build :unsure:

I am doing lots of work on systems for 2.4Ghz for two reasons, one it's cheap to get equipment for this band at the moment and two, I hope to use what I learn on 1394Mhz when I can track down the right parts. Oh, I suppose there is a number three, I need good gear I can use until 1394Mhz is a reality.

Terry

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Terry - 100mW transmitter power in the UK - is that a Radio Ham thing, a protest at 100mW being legal now for the spread-spectrum RC transmitters, or some other loophole?

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Terry - 100mW transmitter power in the UK - is that a Radio Ham thing, a protest at 100mW being legal now for the spread-spectrum RC transmitters, or some other loophole?

It's not a radio ham thing as they don't allow transmision from the air. It's not a protest or a loophole B)

The sad fact is as I have said many times :( broadband is stamping all over me more and more. When flying in remote places I still use 10mW but when flying from my local field (a good 300m + from houses) I now need 100mW where 3 years ago 10mW would do.

I don't like to break the law which is why I am looking to change to 1394Mhz but I am being squeezed out and until I can afford to make the change I will have to do it. 100mW at the height and distance I fly at is not going to cause a problem to anyone so I feel safe in the respect that I am doing no harm. ;)

I am very unhappy that all the equipment I have collected and built over the years is to be useless just because the powers that be put wifi on the same frequency as video senders. :angry:

It has not just effected me or our hobby, there are many many people who used to send video from there satalite receiver to all the tv's in the house that now find them unwatchable. :(

Terry

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Terry - 100mW transmitter power in the UK - is that a Radio Ham thing, a protest at 100mW being legal now for the spread-spectrum RC transmitters, or some other loophole?

Both are different device classes. Our video TXs are analog devices, transmitting an FM-modulated single frequency carrier, which have a 10mW limit.

2.4GHz R/C transmitters, WLANs and all that sort of stuff are spread-spectrum digital modulation devices, for which the limit is 100mW.

Edited by Kilrah

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WoW seeing this thread takes me back! It dossnt even have my 5.8Ghz 4 way system here so it must be on another thread :)

The link you posted shows a unit with no patches, adding them with nice short low loss cables is half the battle!

I must admit I used to love my 4 way system and used it for years but now prefer my auto tracking 14dBi patch, it works well without the need for CP aerials.

Terry

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