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yb2normal

New receivers appear to have RSSI

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I've tested out a new receiver that mates to my 5v 2.4ghz transmitters and it appears to have both a 'carrier present' and RSSI pin on it!

I've thrown together a quick page with a picture:

http://www.yb2normal.com/bwav200autorxhacked.html

I guess now I will have to build myself a diversity receiver :)

Bill

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It's good to know. The reciever looks nice! Do you have any idea how fast carrier detect output is? That is how soon it will show dissapearence of the carrier signal after the actual event?

Regards,

Val.

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Hi Val,

As near as I can tell it is instantaneous, or at least as fast as I can perceive it.

I suspect I can set up a test to actually measure this on my dual trace scope, but I'll need to figure out how to do it.

Regards,

Bill

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How soon will you have them available?? I already have my stuff ready to go for a diversity receiever setup, I was about to buy 2 of lawmate receivers but these new receivers look like what I was wanting.

Pricing??

Thanks much,

Matt Klarich

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Hi Matt,

They are available now to anyone who asks (I've only posted about them on rc-cam). Please email me for details.

Keep in mind these are only compatible with the 5v line of transmitters. They will not operate with the 12v line of transmitters.

I did some further testing on my scope. The Carrier Present line stays high while the RSSI voltage is within range. In other words, right when the RSSI voltage bottoms out (at around 0.9v) the Carrier Present line goes low (not pulled to ground, just a logic low of around 0.5v). It instantly goes high when the RSSI voltage lifts off the bottom.

Regards,

Bill

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Darn it, I wanted to use it with my 3 watt 2.4 tx I bought from you a couple months ago. Is channel spacing different??

Thanks much,

Matt klarich

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The frequency is different on the new equipment, and they altered the way they used pre-emphasis and de-emphasis circuitry.

I believe that Mr. RC-CAM discovered RSSI on the receivers that mate to the 12v equipment.

Regards,

Bill

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I did some further testing on my scope. The Carrier Present line stays high while the RSSI voltage is within range. In other words, right when the RSSI voltage bottoms out (at around 0.9v) the Carrier Present line goes low (not pulled to ground, just a logic low of around 0.5v). It instantly goes high when the RSSI voltage lifts off the bottom.

Thanks, it sounds like "carrier present" is redundant. The reason I asked the question is the old problem of multipath interference which corrupts video signal even when RSSI shows signal present. I was hoping that Carrier Present may be quicker or more sensitive during multipath problems, any comments?

Regards,

Val.

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As an experiment I'll set up a situation where I can consistently produce some multipath (shouldn't be hard in my basement) and watch the result on both the video screen and the scope. Hopefully the loss of video corresponds with the loss of the carrier.

For what it is worth, the RSSI changes seem pretty darn fast, when I block the antenna. I'm not sure what it will show when hit by multipath so I'll look at that too!

Regards,

Bill

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Hi Bill,

I just received a 1 watt 900mhz system from Microtek with this new type of switching receiver.

From my brief tests today, my cheapo 1.2 ghz 800mw transmitter/receiver with stock antennas gives a better signal with less noise than this new system.

I wonder if they changed the emphasis on this receiver also.

I have a friend with the older style (super circuits) receiver and will see if reception is any better using that one.

I am beginning to think 2.4ghz really is the way to go.

Brian

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Well that sounds like a bummer.

What sort of noise? Are there 900mhz cordless phones operating within range?

If you are in a RF "rich" environment then 2.4ghz might not solve your problem either.

The good part about using the illegal 1.2ghz systems is that it is a very uncrowded band ;)

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Hello Bill,

I set up both systems with the receivers 5 feet apart, the transmitters 1 foot apart with a transmit distance of 100'. Both receivers were elevated 7' off the ground. I powered each system one at a time and compared received signal quality. The 900mhz system had color blooming, and a snowy affect in some portions of the picture while the 1.2ghz was clean. The 900mhz seemed to be much more sensitive to multi path I think. As I moved around the receivers the picture would get better or worse with the 900mhz but it had no effect on the 1.2ghz.

I am the guy that can walk by a portable fm radio and it will change received stations. What's up with that?

I am going to take them both out to the flying field to get a better feel for what is going on.

Brian

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I am the guy that can walk by a portable fm radio and it will change received stations. What's up with that?

Well it is clear to me that you are one of those guys who must spend the rest of their life with tinfoil wrapped around their head :D

So when you use the Microtek receiver sold to you with the 900mhz tx, it gives you these poor results?

It is a full 1 watt tx like you said?

Something doesn't seem right.

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Bill,

The tin foil and a ground strap may be in my future ;).

Yes I am using the new receiver with the full one watt transmitter as advertized by Microtek.

I just got a call from Microtek and they said to keep them posted and will make good if it doesn't work out. It may be possible that the manufacturer sent out the wrong type of receivers even though they were purchased at the same time. It does receive but may have a pre/de-emphasis issue. I need to double check everything. The Microtek folks are very nice to deal with as I'm sure are you.

I will be going out to the field tomorrow for more testing, it should be up to 20 degrees from the 6*F now.

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Ok, I think I see the problem now.

It looks like they offer equipment from the same manufacture that I use. If that is the case, then the 1w transmitter they show is actually a 1.2ghz model. The low frequencies on these 1.2ghz transmitters overlaps with the high frequencies of the 900mhz transmitters.

I bet that you are limited on the channels that seem to match up between your tx and rx.

Bill

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They said they do buy from Lawmate like you, but that the transmitter is made in a sister factory. The unit works with all four channels on the receiver.

The receiver for the 1.2 system just went out, it acted like a bad video connection where if you moved the connector the signal would go in and out. I took it apart but found no bad solder joints. I took the can apart and found that the unit is PLL capable with a Zarlink SL1461SA but it's upper range was designed for 800mhz.

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It sounds like they are going to take good care of you, hopefully the 900mhz issue is resolved.

Regards,

Bill

Edited by yb2normal

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Didn't get out to fly the 900mhz system, too cold for my video recorder to work properly. I did get to check the current draw of the new amp, 530ma.

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Getting back to the diversity system,

Do you plan to switch antennas during the vertical sync?

Is there a way to choose the cleanest signal vs. the strongest signal?

I have read of some systems comparing the video output signals of the receivers for determining the best signal to use vs. the received signal strength.

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Hi Brian,

No, nothing quite that fancy. I'm just thinking of doing what cyber-flyer did, which is to compare the RSSI voltage from the two receivers and switch to the one with the best signal.

Based on my goal for such a system, and looking at cyber-flyer's results, this looks like a great way to do it.

Regards,

Bill

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