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HomeRC & PowerAircraftHelicopterRadio - Spektrum DSM › Remote RX wire lengths matter?
01-15-2010 10:27 AM  8 years agoPost 1
LaurenceGough

rrElite Veteran

UK

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Hey guys,

Just a quick (possibly stupid) question but I would like to know if different remote RX lengths matter.

If the signals arrive at different times etc...

If it's optimal to have the same lengths I would rather do that.

I'm planning to use two remote RX's.

I'm going to use the new Mikado V-Bar unit (With built in main RX) so there will be no Spektrum main RX.

I'm sure it doesn't matter but Spektrum doesn't really go into the technical side much.

Thanks in advanced,

Laurence

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01-15-2010 01:26 PM  8 years agoPost 2
Avropilot

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Murfreesboro, Tennessee

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I don't think it matters. I have flown with no antennas (they broke off) for a year or so. No problems at all.

Waiting for parts

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01-15-2010 02:14 PM  8 years agoPost 3
Rafael23cc

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Junction City, KS

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I don't think it matters. I have flown with no antennas (they broke off) for a year or so. No problems at all.
Oh wow, I never thought somebody could be that irresponsible. And then make a suggestion that it is ok for somebody else to try it.

On the other hand, I'm glad that the OP is not talking about antennas. He is talking about the remote receivers on a 2.4 system and the lenght of the cable that joins the main RX to the remote RX.

Technex:

I'm by no means an expert in 2.4 technology. I know that Spektrum sells "extensions" for their remote receivers. I have read multiple articles where it is suggested to place the receivers as far away from each other as possible (this is on giant scale plank applications), and they suggest to use the extensions to achieve this. So MY conclusion is that you should be ok if you stay within the prescribed lenghts of the extensions.

Rafael

Keep your feet on the ground, but your eyes on the sky.
Team Heliproz.com

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01-15-2010 02:57 PM  8 years agoPost 4
LaurenceGough

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UK

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Thanks,

You know what, I think I'll just play it safe and order two 6" extensions. I've been fine with my AR7000 and remote RX only a few inches away so far (Polarised).

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01-16-2010 12:36 AM  8 years agoPost 5
9387ASH

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UK

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In theory yes; there will be a slight delay between the 2 incoming signals hitting the antennas.

In reality this delay is negligible. With 2 antennas separated by 1 metre, the delay is going to be approximately 3.9 nanoseconds ( 1 nanosecond = 1/000 of a microsecond ) taking a typical velocity factor of 0.85 for coax etc.

The on-board processor in the remote receiver and main receiver can handle a Data rate of 1 MBPS. This basically means that the timing is going to be in the order of 1 microsecond.

As the delay is approx 4 nanoseconds which is 1/250 th of 1 microsecond.

So as you can see, the delay is of no concern.

Please note that the figures above are approximate but close enough for demo purposes.

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01-16-2010 12:50 AM  8 years agoPost 6
dkshema

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Cedar Rapids, IA

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As for Avro -- the question was about the length of the cable connecting the main RX to the satellite RXs. They're sold in several lengths, no the propagation delay won't be a problem.

But flying the the antenna wires missing -- that's plain irresponsible.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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01-16-2010 03:00 AM  8 years agoPost 7
Justin Stuart (RIP)

rrMaster

Plano, Texas

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I have one extension which is 6 inches long and one which is 2 feet long on the same receiver (on a plank) and they work fine together.

Avant RC
Scorpion Power Systems
Thunder Power RC
Kontronik Drives

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01-16-2010 03:59 AM  8 years agoPost 8
Avropilot

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Murfreesboro, Tennessee

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Wow my responsibility is in question here. I guess the experts have spoken and now some knelling and worshiping is now in order.

dkshema
I'll start with you here. Lets talk responsibility. Your post here Tells some poor guy he has the wrong switch and he needs to order a Futaba one for his Spectrum radio. However I see a nice big fat plate of crow was had with a helping of humility on the side. You misread a pic and assumed he needed a different switch. Fact is you were right had you not jumped to conclusions. Unfortunately thats exactly what you have done here. I have flown with a antenna missing. I didnt know it till I took the canopy off to clean the heliand noticed it. Could have been that way more than a year for all I know. I never look at the remote unless I crash and need to remove it. One should always keep his "Errogence" in check.

Rafael23cc
Once again My responsibleness would be absolutely none of your business. We have a guy we call the "field police" at our club. My hunch is you are that guy at yours so let me give you some friendly advice. If you see a group of guys at your field standing together talking enjoying themselves, and when you walk up they get really quiet. It is probably because they could care less about any of your lame a$$ opinions. And they are probably tired of hearing it. Fact is, you may very well be the brunt of the joke. Think about that next time you decide to take someone elses inventory and classify them with words like "irresponsible".

Assume nothing.

Flame suit on and fully charged.

Waiting for parts

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01-16-2010 05:55 AM  8 years agoPost 9
dkshema

rrMaster

Cedar Rapids, IA

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Arrogance, not Errogence.

The original post began with the switch owner wondering if he had gotten the wrong switch.

I saw a picture, it looked like a DPDT switch. I'm familiar with the larger 1/4 inch shank toggle switches sold all over the country that have the larger body as shown in the picture.

I know the Jewel switches are smaller overall, that they have a smaller diameter shank than normal and that Futaba uses them. They have for many years.

The switches on the Tower Hobbies site for Futaba are the small Jewel switches, and in my original post, indicated that the fellow might want to look for Jewel switches, and gave him some suggestions as to where to look. I also noted that I didn't think the switches on the Tower site wouldn't work as they were only SPST switches.

Later, a better picture was posted, clearly showing the neat little PWB that Spektrum uses, and that I had mistakenly identified the switch as a DPDT in my first post. (I still think those little boards are a very nice manufacturing touch). I also noted that the Jewel Switches sold by Tower as Futaba replacements would "drop right in", as that little PWB would make the swap easy. I pointed out that the PWB is there so you don't have to make individual wrap/solder joints to the switch posts. It seems I also noted that the larger body switches apparently can be had with smaller diameter shanks.

I corrected my earlier post, up front, publicly, and admitted I was in error.

What did I do wrong? Make a mistake, correct it, and admit it? Not crow, no one forced me to "fess up". I believe in being honest in what I post, and if I make a mistake, I happily, and freely admit it. It's not the first time this has happened, it probably won't be the last.

Responsibility is admitting freely that a mistake was made and correcting the mistake as soon as it's discovered without being forced or coerced or chided into doing so.

-----

As for my post regarding responsibility. Working with this information:
I have flown with no antennas (they broke off) for a year or so.
it appears that you knowingly continued to fly with missing receiver antennas for about a year.

I only go with the information as presented. It would also appear that I was not the only person to come to the same conclusion looking at the same evidence.

No need for a flame suit, no need to continue to beat this to death. And no need to hijack this thread.

-----

As for the length of cables in the Spektrum RX, I think they sell 6 inch, 9 inch, 12 inch, 24 inch and 36 inch cables. At those lengths, propagation delays should not present any problem.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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01-16-2010 08:37 PM  8 years agoPost 10
Rafael23cc

rrKey Veteran

Junction City, KS

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I have no further input. Dkshema is much more elocuent than I am.

And no, I am well respected in my neck of the woods.

Rafael

Keep your feet on the ground, but your eyes on the sky.
Team Heliproz.com

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01-17-2010 09:58 AM  8 years agoPost 11
LaurenceGough

rrElite Veteran

UK

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Thanks for the replies.

Field police, haha sounds like me sometimes hahahaha.... Someone's gotta keep everything in check .

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