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HelicopterRadio - Servo - Gyro - Gov - Batt › Can a 900mHz downlink interfere with 35mHz R/X
01-25-2007 09:43 PM  10 years agoPost 1
coffman

rrApprentice

NL

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Radio Boffs, please tell me if there is any way my 900mHz downlink will cause my 35mHz receiver to go into failsafe.

Thanks,
Coff.

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01-26-2007 02:46 AM  10 years agoPost 2
ka6fty

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Sacramento, Ca.

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Don't Do It!! You'll go back in time.

Just kidding. It should work fine. Just make sure you do a range check with the downlink off and on to compare results. If the range test with the downlink on is substantially worse, don't fly.
I also like to try it with the heli in different positions.

"Don't put your fingers where you won't put your face"

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01-27-2007 11:19 AM  10 years agoPost 3
coffman

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NL

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If it is ok on the test will it always be ok, if you keep all hardware and aerial positions the same as on the test?

What if down link transmitter is positioned on an underslung mount than can pan around etc, is this worse as you cannot range check in every possible position?

Thanks,
Coff

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01-27-2007 05:55 PM  10 years agoPost 4
onewasp

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USA

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Hey guys------been a long time since I was actively involved in Radio Theory but just "How" does/can 900MHz bother the Rx tuned to 35MHz???????

It has to be a "kajillion" images away.

I can understand the attenuation via the mass but I honestly don't 'get' any other RF concern. Elucidate please.

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01-27-2007 09:12 PM  10 years agoPost 5
9387ASH

rrElite Veteran

UK

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Theoretically it shouldnt have much effect , however..... it is possible for the RF to get onto the pcb track and cause interference. What receiver are you going to be using ?

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01-28-2007 11:41 PM  10 years agoPost 6
Skeeter Pilot

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England

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Isn't there something called 'IF', intermediate frequecy? Apparantly it can swamp the receiver particularly when near to buildings.

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01-29-2007 12:51 AM  10 years agoPost 7
onewasp

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USA

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IF = intermediate frequency (super het.) results in "images" I referred to above. Each image is (should be) weaker than the one preceding it.

Reflection (your comment on buildings) is really another topic.

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01-29-2007 01:24 AM  10 years agoPost 8
Skeeter Pilot

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England

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So are you saying it can't interfere?

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01-29-2007 05:47 PM  10 years agoPost 9
onewasp

rrApprentice

USA

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Mac Man is a better source--- particularly since you are on the same bit of geography.

In radio I would NEVER say "never"------however if IFs are your concern then I would say no.

On reflections, I have experienced reflected RF(long before PCM) "bouncing" my A/C around a little. That however was a metal building and while you could count on a "bounce" if you flew close to it no one at that particular field ever had a crash because of it.
That was in the very early 70's and was encountered on both 72MHz and on six meters, but NOT with dual conversion Rxs.

Since then I have never had a similar experience-----but then again 100% metal buildings are not that common, at least here.

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HelicopterRadio - Servo - Gyro - Gov - Batt › Can a 900mHz downlink interfere with 35mHz R/X
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