Klarich Electronics/BlackWidow Diversity Receiver
Posted 03 March 2005 - 07:03 PM
Multi-path interference occurs when a signal originating from a video transmitter is received by a receiver that also receives the exact same signal a split second later because the 2nd signal has bounced off of an object and arrives a split second after the original signal. Sounds kind of confusing but it is the source of much of our troubles with video systems. I have been trying out different antenna configurations for 4 years trying to get amazing video, believe it or not a simple rubber duck antenna and small patch antennas have given me the best results. Many patch antennas that have higher gains to increase receive sensitivity also narrow their beam width which reduces the area that an airplane can fly in without having the antenna pointed at it.
The system works as such. My circuit board is designed to switch between 2 video receivers that are set to the same channel. My circuit decides which receiver is getting the better signal and then switches to that receiver in-between frames. You don't see the switch!!!
This video shows exactly how the diversity receiver works, to allow the viewer to know when the diversity receiver has actually switched we disabled the audio channel on one of the receivers. This allows the viewer to hear when the switching occurs.
Please email us with any questions or post them here.
Klarich Electronics, LLC
mklarich-AT-klarichelectronics.com or Bill Strong [ williamhstrong-AT-yahoo.com ]
Posted 04 March 2005 - 12:00 AM
Posted 04 March 2005 - 09:49 AM
The new unit is all black to match the receivers. I am still surprised no one asked me what the heck that thing was on the tripod, but then again my airplane was in the shot...along with my wife..... Probably should have put her first
Edited by mklarich, 04 March 2005 - 09:51 AM.
Posted 04 March 2005 - 02:19 PM
Posted 04 March 2005 - 02:51 PM
How much is one of them there diversity receiver things any way?
That sure is a nice looking airplane you got there how dose it fly and where can I get one?
Posted 04 March 2005 - 03:28 PM
I'll jump in with my comment since Matt and I differ on our choices of antennas. He's happy with the standard whips and I like to fly with high gain patches.
Those aerials look very close together, dose it improve the dropped frame rate at long range by much ?
The 14dbi patch antennas I'm using now are linear polarized, so when I set them up I orient them so the polarization axis's (axees?) are 90 degrees from each other. That way I'm effectively getting both horizontal and vertical polarization.
In my situation, spacial diversity is playing second fiddle to polarization diversity. As you suspect Terry, spacial diversity becomes less critical at longer ranges due to good-ol' geometry.
*** Dave, the units will start at $299 and will include the same antennas Matt pictures. I'll try to get some pictures done today but I am fast running out of hours in the day.
Posted 04 March 2005 - 04:58 PM
Posted 04 March 2005 - 05:07 PM
I will have info and pics up shortly.
Regarding antenna distance. A wavelength at 2.4ghz is 30cm long. It doesn't take much distance between antennas to make a huge difference. Just look at wireless routers for computers, their frequency is only 50mhz away from us and their antennas are closer together then mine.
More info will be up later this weekend, please ask any questions you have. I need to get a faqs list setup for the unit.
Posted 05 March 2005 - 12:22 AM
It really looks good!
Are you comparing RSSI outputs to decide which receiver to switch to?
The problem to be able to use other RXs would then be calibration to output levels if I understand correctly?
And maybe it's stupid, but what about using 1 whip antenna and 1 patch? So when you are close to you the whip will grant you omnidirectionality, and when flying far away (where angle is reduced according to the good old geometry you were talking about) the gain of the patch, which of course is pointed roughly in the good direction, will give you the needed range...
Posted 05 March 2005 - 06:47 AM
On the one hand, as contributing members, we are chomping at the bit to tell you every detail of how the units work. But as vendors, we have a responsibility to our companies not to get to detailed.
Where appropriate we are happy to share details that we gleaned from public domain. But our individual inspirations must remain secret
Ok, now to your question. Yes, the circuit compares RSSI voltages between the receivers. Matt's experiments have shown that of the samples tested, the RSSI ranges are surprisingly well matched. The receivers used are identical so we had hoped this would be the case.
Regarding antenna selection, I'm really excited to see what people end up doing. Your idea sounds plausible, now we just need to get some units in the field for everyone to try out their own theories.
Someone asked on another thread about indoor use. This is perhaps the most challenging environment to work in and theoretically, a diversity receiver should help these situations. I expect that once we get the units in the field we'll have a better of idea of where the diversity switch will shine. I also expect to hear about some creative antenna placements to help with indoor apps... As we learn how people use the units we'll post on our respective websites with tips and tricks that we learn.
Posted 05 March 2005 - 12:13 PM
Posted 05 March 2005 - 01:09 PM
Below is a picture of an almost completed unit. The labels are arriving early this coming week and units should be available for sale at the end of the week. If all goes well they will be ready to ship friday.
Posted 06 March 2005 - 07:00 PM
Posted 06 March 2005 - 07:25 PM
Kilrah, using one omni and one patch is the right combination - it's exactly how I end up setting up my antennas. Except that I run my tracking bi-quad instead of patch.
Posted 07 March 2005 - 05:33 AM
CH1: 2414 - CH2: 2432 - CH3: 2450 - CH4: 2468MHz
Do you think it is possible to retune BW receivers to a slightly different frequency?
Posted 07 March 2005 - 05:56 AM
Posted 07 March 2005 - 07:12 AM
I do use audio to send telemetry data, but audio carrier offset can be adjusted from Felsweb TX (they have a pot for subcarrier offset), I don't think audio will be a problem to match.
Posted 07 March 2005 - 09:27 AM
If needed I can add a switch to the current model that the user can turn the audio channel switching capability off, so you will always be listening to audio from one of the receivers while the video still switches.
How many receivers are you running in your diversity receiver?
Edited by mklarich, 07 March 2005 - 09:29 AM.
Posted 07 March 2005 - 09:49 AM
Audio switching wasn't a problem for me. A frame may be dropped during switch, I never looked - the overall performance is not affected. Video quality is more sensitive to switching, especially when I fly in the dark when any noise in the picture adds to confusion.
If you need a tester, I volunteer.