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Mr.RC-Cam

Maxim's Loss-of-Video-Sync Alarm IC

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Updates to the ORACLE Project:

* June-21-2007: Oracle is released for sale on the dpcav.com web store.

* May-29-2007: End of Beta test. V1.4 firmware released.

* Apr-09-2007: Updated Instructions for beta testers, Click Me.

* Apr-03-2007: V1.1 firmware released.

* Mar-13-2007: Beta units with V1.0 firmware are ready to ship.

* Feb-24-2007: Beta Test Sign-up Details: Click Me..

Start of original Oct-11-2006 Post

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For those that are not familiar with wireless video diversity Rx's, they use two antennas, placed a distance apart. This is called spatial diversity and it helps to eliminate multipath fading (a big nuisance in our application). It can also be used in a polarization diversity arrangement, which is effective too.

To help those that want to create their own design, Maxim has a convenient new IC that can detect loss of sync in under 5mS (<80 scan lines): Click for MAX7461 details. This IC, along with RSSI sampling, could allow two Rx's to form a very intelligent diversity Rx. Of course additional electronics is required (typically a microcontroller).

Speaking of diversity Rx's, does anyone think there is room in the market for a *commercial* design that would sell for $199 USD? If so, then share your wish list here! The main thing that would be good to know is if whistles and bells are wanted (fancy case, LCD status display, internal battery pack, etc.), or should lowest possible cost be the goal? Keep in mind that it would need to appeal to the masses and not specifically to the DiY crowd.

The direction I take will depends on the feedback. I'd like to do this project, but I would rather not create something that has little demand. My thoughts are that it would be a killer solution if it was under $200, but I am a biased bystander. :)

Edited by Mr.RC-Cam

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RC-Cam, in my opinion, the best diversity receiver would be one that is modular. What I mean by that is, a diversity RX with two or more video inputs, and two or more RSSI inputs, and one video output. Keep the receivers seperate, that way people can hook up 2.4ghz, 1.2ghz, 900mhz, or even 400mhz as long as the receiver has an rssi output. Or the option to mix them up if they want, between 2.4 and 900, etc. etc

And sell receivers alongside with it as seperate components. That way, people who already have receivers will be more likely to buy your system as they won't have to purchase 2 receivers, just one more to add to the one they already own.

Edited by eickst

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Dam !

Just when I got my PIC detecting video loss.....

As far as a commercial design I think a good solid basic job would sell best, possibly be able to upgrade to the extra bits ?

Terry

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I think there would be a great demand.

Look at this THREAD to see the response when Anthony hinted at being able to make them...

Also, as flying by video gets more popular, folks are going to want to increase the video link's performance. A few vendor sites have even popped up recently selling decent gear at great prices. Now I even hear of someone else creating another headtracker.

I think a basic diversity RX would be very welcome.

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Thanks for the comments!

... the best diversity receiver would be one that is modular.

I considered that and originally went off in that direction. However, it would become a technical support burden. The RSSI signal scaling varies with the different Rx's, even with the same maker, and the video levels need to be well matched. So, I have decided to avoid a "universal" diversity box that uses customer provided equipment.

Look at this THREAD to see the response when Anthony hinted at being able to make them...

Thanks for the link. I see that he is using the Airwave modules. I'm planning to use them too since they have good performance and have been a favorite around here. I decided to not use Lawmate equipment since I wouldn't want to step on Bill Strong's efforts at BWAV.

I think a good solid basic job would sell best, possibly be able to upgrade to the extra bits ?

From what I have seen on the various forums, price is everything when it comes to wireless video equipment. So, I agree with you that a basic model, sold at a low cost, would get the most attention. Especially if it worked well. :)

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I forgot to add this link to his high altitude, long distance flight. In the post you can see some details of his diversity RX...

LINK

Here's a teaser picture...

a949736-212-IMG_0312.jpg

I'm not interested in doing any beyond visual range stuff myself. My ideal situation is to follow other model airplanes around. Anything that increases the integrity of the video link will increase my confidence in the system and make it that much more fun.

I would want a bare bones system.

No internal batteries, no LEDs except perhaps an "on" indication, and the only thing nice to have in the case is a sturdy 1/4 20 nut/nutplate for mounting

Edited by rob10000

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Hmm, didn't think about the differences in RSSI values. The main reason I suggested it is because alot of people who would want a diversity system already have one receiver, and may be more inclined to purchase a product that saved them some money.

Another reason is that some of us prefer frequencies other than 2.4ghz. I realise that a 2.4ghz system is pretty much globally accepted, but I get much better range performance and less "glitches" when I use 900mhz or 1.2ghz (not cheap hong kong ebay 1.2ghz). The antennas are larger, but to me it pays dividends on range and overall performance. Keep in mind however that I have not had an aerial mounted transmitter yet, all of my projects have been stationary to this point or only slowly moving, no fast motion or rotating of any parts of the transmitter as we would see in an RC perspective.

Oh, and keep the price under $200 please. You don't need vacuum molded plastic cases to sell these things.

Edited by eickst

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My focus will be a bare bones 2.4Ghz diversity Rx with an aim for a $189 USD street price. No frills, just function.

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I had started designing one for my own use but let that aside because of an obvious point being versatility...

BWAV have made one, which only works with their frequence set 1. Too bad, I have gear on set 2. I also have quite a lot of gear that works on other frequencies, so no compatibility. I don't really feel like buying even more stuff...

As far as making it for my stuff if I was using a simple RSSI sampling / LM1881 sync ref / MAX4311 switch solution I'd have to tune it for 2 or 3 different receiver sets like Mr.RC-Cam said.

So considering that, I'd only be making one if it was "plug-and-play". That is possibly even ignoring RSSI not to have to tap inside the RX and especially to calibrate, and only relying on the video signal.

To avoid calibration, couldn't you simply compare both RSSI's and switch to the higher-meaning one, not caring about the actual value?

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Now HERE is a thread to get me all excited! I have been dreaming of getting a diversity RX forever...but price was too prohibitive. I would go after one immediately if it was less than $200! Heck, even if it was a tad over!

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So considering that, I'd only be making one if it was "plug-and-play". That is possibly even ignoring RSSI not to have to tap inside the RX and especially to calibrate, and only relying on the video signal.

When using a dual Rx design, the nice thing about including RSSI is that it can be used to predict impending signal loss. So, proactive action can be taken. In the grand scheme, a combination of video sync detection, and RSSI monitoring, can be paired up to help create a very robust solution. However, a design that uses only one of these things would save cost; some Muntzing may happen after testing is performed.

Truth be told, I have something in mind that is even more interesting than two Rx's wrapped around sync detectors, A/D's, and microcontrollers. But, mums the word. :)

To avoid calibration, couldn't you simply compare both RSSI's and switch to the higher-meaning one, not caring about the actual value?

I thought about that, but it comes with little gotchas. For example, the active RSSI can be positive or negative, which adds another user setting to get wrong. Also, by knowing the RSSI's scaling, it is possible to use some intelligent hysteresis during the switching decisions.

But having said all that, I think the main reason I want to avoid a universal box is because it would require the user to flip switches (and/or adj pots), ID and solder to the Rx's internal RSSI signal, adjust the two video levels to match, and tinker. Those of us on this forum enjoy that. However, there seem to be more folks out there that just want things to work without any fuss. In order to serve them, the solution would need to be plug-n-play.

Depending on what I find as the project unfolds, I may change my opinion. But for now I'm sort of sold on the ready to use concept that is low cost.

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I totally agree, but my point is that as you said yourself people try to always get their stuff for as cheap as possible. I wonder if they'd want to buy new gear replacing what they already have :unsure:

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I wonder if they'd want to buy new gear replacing what they already have.

I worry about that too. Those that have a significant investment in wireless video gear will not be interested. But those that are ready to upgrade their cheap import video Tx and Rx, or are just joining the hobby, would be the likely customers.

It's all a guessing game. Frankly, anyone that takes the time to develop these unique hobby items are just plan mad. There are simpler ways to make a living. :)

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I wholeeartedly agree with the above :lol:

That's why the most important thing is to develop stuff you want for yourself anyway ;)

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Interesting thread. There seems to be a lot of interest in these Diversity receivers, and unfortunately the BWAV unit has priced itself out of the mass-market.

I have a design ready to go which uses a couple of airwave modules. Results so far have been very interesting, as the videos floating around my neighborhood have probably shown.

Late summer I got a little diverted with the announcement of an interesting receiver module which already integrates a dual-antenna diversity system. This would of course have allowed the price of these systems to be slashed.

Initial testing has shown that these might not work for our application though, they don't perform as well as a dual-airwave Rx even with a very simple algorithm for determining when to swich receivers.

Anyway, summer flying days are over, so the dual Rx design that I have been using over the summer should be available (probably in kit form) pretty soon.

On the subject of a simplified multi-rx diversity system, using existing receivers, I have had a lot of queries about the possibility of this. From a wiring point of view its not as nice as an integrated system (especially finding the RSSI signal), but it would allow existing receivers to be used.

I would have thought that RSSI polarity detection would be fairly simple... if one assumes that the Tx is close by when the system is powered up. RSSI calibration could also be done fairly simple, with a calibration button. Use two (or more) identical Rx antennas, move the Tx to various distances (or replace the Tx antenna with a dummy load), and calibrate. Of course if the location chosen for the calibration procedure lends itself to multi-path loss it wouldn't work, but the local flying field should work.

-- Anthony

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Oh I just remember another thing. I had found somewhere some "generic" 2.4GHz receivers that had a display and 2 buttons. With those you could set any frequency in the 2.4GHz band and even a bit further in 1MHz steps. That would be an idea for a more universal solution :)

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Late summer I got a little diverted with the announcement of an interesting receiver module which already integrates a dual-antenna diversity system.

That is not good to hear. That is one of the solutions I had in mind. Did you actually try one? If so, why didn't it work out?

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This sounds like an interesting project, that I may be interested in. I know people are using the BWAV unit with good success, but it's a bit pricey at $325. So low cost is important for sure. Most important, however, would of course be performance. If it doesn't work good at all, then it doesn't matter how much it costs. :) Compatibility is also an important issue. I have the BWAV Tx/Rx's on frequency set 1. For me personally, I would want it to work with the equipment I already have.

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My next problem is getting hold of the MAX6471's. I want too many just to ask for a sample this time and the web site is telling me they would get in touch when I tryed to order some. Never as simple as you think it will be :rolleyes:

Terry

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Compatibility is also an important issue. I have the BWAV Tx/Rx's on frequency set 1. For me personally, I would want it to work with the equipment I already have.

A plug-n-play solution would not be universal, which limits the compatibility. That is one of the problems that has been discussed here. What I had in mind is not fully compatible with BWAV. It would be compatible with Airwave and perhaps Felsweb.

With anthonyrc's soon to be released diversity rx, I'm not sure if I should create one too. There isn't much room for competitors in this tiny market, especially since we'd both be attempting to sell something that is similar. I think his will be a DiY kit, but no doubt some enterprising hobbyist would assemble these on the side and resell them. I can't compete with hobby businesses.

I'll have to think about this some more. Maybe I'll reconsider the design goals. Or, perhaps I'll just find something else that needs to be developed for this unique hobby. :)

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RC-Cam, I don't know if you've thought of this, but why not have one receiver, and 4 antennas all hooked into an RF log detector? Those would generate an RSSI signal, should be cheaper than receivers, and would allow for as many antennas as you wanted. There are several good smt antenna switches on the market, the only issue you may have to look into is how to couple the antenna to both the switch and the detector with minimal loss.

Oh, and that would make the system cheaper for everyone since we could all use whatever receivers or antennas we wanted.

Edited by eickst

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... the only issue you may have to look into is how to couple the antenna to both the switch and the detector with minimal loss.

That is a huge issue. If this was VHF or UHF, it would be a slam dunk. However, all the microwave RF rated antenna front ends I know of require critical designs, very finicky PCB layouts, and careful sardine can shielding. Of course it's possible, but isn't a solution I feel comfortable with. I'll have to leave that method up to a RF superstar. :)

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That is a huge issue. If this was VHF or UHF, it would be a slam dunk. However, all the microwave RF rated antenna front ends I know of require critical designs, very finicky PCB layouts, and careful sardine can shielding. Of course it's possible, but isn't a solution I feel comfortable with. I'll have to leave that method up to a RF superstar. :)

They have couplers that will do it, i think the best one I saw was a 20db one, not too shabby, but it costs more than a receiver does!!! Cheaper to do it with 100 receivers all with their own RSSI output than to try to do 100 antennas with 100 couplers, 100 detectors and a 100 way antenna switch.

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With the receivers so cheap, multi receiver is the only way to go at 2.4Ghz. Anything else is just asking for problems.

Terry

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Is anyone going to get a batch of these ? Ive been quoted $50 just for shipping. At this price Im going to go back to plan A :(

Terry

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