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Old May 01, 2009, 03:12 AM
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Renton, WA
Joined Nov 2006
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Futaba 3PM 2.4G receiver antenna length

I have purchased online a Futaba 3PM 2.4G system based on reviews, etc. but never seen it in person. I can not seem to find a decent picture of the 603FF receiver that shows the actual length of the antenna wire. It seems that pics I've seen in trucks (BL stampede application) look stubby (short), but I don't know if people have trimmed it down or it comes real short.

While I'm waiting for it to arrive, I wanted to consider whether it would fit under the body ok or need to extend thru. thanks for any info/pics.
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Old May 01, 2009, 09:27 AM
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Champaign
Joined Apr 2003
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Hi Vashon10,

The antenna length on the R603FF is 210mm long.

Trimming any antenna is definitely not recommended, doing so will affect the range and signal reception.


Sincerely,
Krysta
Product Development & Support Specialist
Futaba Service Center USA
service@futaba-rc.com
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Old May 01, 2009, 01:33 PM
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Thanks krysta. I am really confused now at pics I've seen that have really stubby receiver antennas. I thought that was one of the benefits (albeit minor) of 2.4G was not having that antenna sticking up out of the body like AM does.
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Old May 01, 2009, 02:10 PM
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You're welcome.

If you are looking at some of the pics on our website, the picture was reduced to fit the page and the complete antenna is not shown.


Sincerely,
Krysta
Product Development & Support Specialist
Futaba Service Center USA
service@futaba-rc.com
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Old May 01, 2009, 02:21 PM
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Krysta, just a followup... when I experimented with my AM antenna in two configurations: a) typical antenna holder length with it spirally wrapping back down on the outside of the holder and b) an antenna holder that extended the full length of the antenna wire (yeah, looked funny) ... I found no difference in the response.

So my question to you is, do you think there is a difference in response for this system if say 1/3 (or some fraction) of the antenna length did not extend vertically, but instead was wrapped spirally back down the outside of the tube. Hope all that makes sense. thanks.
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Old May 01, 2009, 04:56 PM
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Joined Feb 2006
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Quote:
Originally Posted by vashon10
do you think there is a difference in response for this system if say 1/3 (or some fraction) of the antenna length did not extend vertically, but instead was wrapped spirally back down the outside of the tube. Hope all that makes sense. thanks.
I'll be interested to see Krysta's answer, but my expectation is that it would mean a substantial loss of range. Generally speaking you want the antenna on a 2.4 receiver to be essentially straight. The antenna itself is only a couple of cm. long! It's not like a 1m antenna on 72.

What you are proposing is equivalent to shortening the antenna. See Krysta's comment:
"Trimming any antenna is definitely not recommended, doing so will affect the range and signal reception."
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Old May 01, 2009, 06:01 PM
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Quote:
Originally Posted by Daedalus66
I'll be interested to see Krysta's answer, but my expectation is that it would mean a substantial loss of range. Generally speaking you want the antenna on a 2.4 receiver to be essentially straight. The antenna itself is only a couple of cm. long! It's not like a 1m antenna on 72.

What you are proposing is equivalent to shortening the antenna. See Krysta's comment:
"Trimming any antenna is definitely not recommended, doing so will affect the range and signal reception."
Because 210mm is not a couple cm, it is 21cm or 8.3 inches. When I've browsed galleries of installed 2.4G systems, the rec antenna doesn't even extend out of the body. So there is a difference between what I've seen practiced (short ~ 2-3 inches) and what is provided which is 3x that.

I'm starting to think that the difference is taken up in the routing of the antenna. I have my AM rec mounted right next to the antenna tube, so there's essentially no routing. Using the same concept, then that would make for an 8" vertical antenna which by all means would extend outside the body. Thus if I could either "waste" some by routing or double up by spiral wraping, then I could keep it inside the body. I just don't want to deal with an exterior antenna tube that vulnerable to constant bending due to flips or whatever. That's why I'd like to know what my options are without compromising the system. Cutting is out, I know that now.
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Old May 04, 2009, 07:20 PM
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I'll tag onto this same thread with another question. I'm previewing the manual and it talks about PPM and HRS. A little bit of searching around (outside of the manual and annoyingly in searching "hrs" also is an abbreviation for hours) seems to indicate it has something to do with servo response.

Which should I select ( PPM or HRS ) with my Hitec HS-645MG servo (BL stampede) ?

thanks.
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Old May 04, 2009, 08:01 PM
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Quote:
Originally Posted by vashon10
I'll tag onto this same thread with another question. I'm previewing the manual and it talks about PPM and HRS. A little bit of searching around (outside of the manual and annoyingly in searching "hrs" also is an abbreviation for hours) seems to indicate it has something to do with servo response.

Which should I select ( PPM or HRS ) with my Hitec HS-645MG servo (BL stampede) ?

thanks.
I think if you are using Digital servos, then the system will go to HRS mode (High Response System 7ms), if using analogs then PPM (Regular mode 14ms) will be.
Check page 52 of the manual.

Regards,
Doug.
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Old May 04, 2009, 09:19 PM
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Canada, ON, Ottawa
Joined Feb 2006
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Quote:
Originally Posted by vashon10
Because 210mm is not a couple cm, it is 21cm or 8.3 inches. When I've browsed galleries of installed 2.4G systems, the rec antenna doesn't even extend out of the body. So there is a difference between what I've seen practiced (short ~ 2-3 inches) and what is provided which is 3x that.
The antenna itself is about 2cm long. The total length of 21 cm includes the coax cable. What matters is that last 2 cm -- don't fold it back on itself or you will effectively shorten it.

When you look at other 2.4 receivers you get an idea of how short is the real antenna.

It doesn't matter much how you fold the antenna cable. Whether the antenna itself needs to poke outside the body depends on the material. If it is carbon fibre or anything else conductive, the answer is yes. Otherwise it's not critical (but don't put the antenna -- the active portion -- next to metal parts). The antenna needs a clear shot at the signal.
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Old May 05, 2009, 11:44 AM
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Quote:
Originally Posted by DougV
I think if you are using Digital servos, then the system will go to HRS mode (High Response System 7ms), if using analogs then PPM (Regular mode 14ms) will be.
Check page 52 of the manual.

Regards,
Doug.
Thanks. Yeah, I read and reread the manual, esp pg 53 and all it says is how to choose the two, not what the difference is or why one would choose one over the other. Here's what it says...

"The signal mode output from the transmitter can be changed. (PPM/HRS)"
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Old May 05, 2009, 01:15 PM
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Quote:
Originally Posted by Daedalus66
The antenna itself is about 2cm long. The total length of 21 cm includes the coax cable. What matters is that last 2 cm -- don't fold it back on itself or you will effectively shorten it.

When you look at other 2.4 receivers you get an idea of how short is the real antenna.

It doesn't matter much how you fold the antenna cable. Whether the antenna itself needs to poke outside the body depends on the material. If it is carbon fibre or anything else conductive, the answer is yes. Otherwise it's not critical (but don't put the antenna -- the active portion -- next to metal parts). The antenna needs a clear shot at the signal.
Thanks a lot for the clarification. Based on Krysta's answer of the "antenna" length it was not making sense. Now with your clarification, it does make sense. I do just have a regular stock body, so it sounds like coiling the coax to allow internal placement will be fine as long as the exposed wire (real antenna) is pointing vertically.
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Old May 05, 2009, 02:07 PM
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vashon10, the antenna in question in my answer was for the FASST receivers. Your 72Mhz AM antenna can be wrapped as long as it does not cross over itself.

The reason for NOT shortening the FASST receivers is as Daedalus66 says, that the last few millimeters of the antenna is the most important. It was what actually receives the signal. The portion that is coated is just the coaxial portion. Cutting this would cause serious problems.

Also as DougV says, if you are using HRS mode to enjoy the faster response time, you do need to use Digital servos. If you have any analog servos, you need to be in PPM.


Sincerely,
Krysta
Product Development & Support Specialist
Futaba Service Center USA
service@futaba-rc.com


Quote:
Originally Posted by vashon10
Krysta, just a followup... when I experimented with my AM antenna in two configurations: a) typical antenna holder length with it spirally wrapping back down on the outside of the holder and b) an antenna holder that extended the full length of the antenna wire (yeah, looked funny) ... I found no difference in the response.

So my question to you is, do you think there is a difference in response for this system if say 1/3 (or some fraction) of the antenna length did not extend vertically, but instead was wrapped spirally back down the outside of the tube. Hope all that makes sense. thanks.
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Old May 05, 2009, 02:16 PM
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You must be careful in how you distort a coax cable. It is a complex item, an inner conductor with a rather exacting spacing between it and the outer sheath. If you bend it to tightly or crimp it, you severely damage it and can create a catastrophic failure in so far as being able to transmit the desired signal. Any crimping or deformation changes it's characteristic response greatly. Check out "coax cable" on "how it works" using Google or some other search engine.
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Old May 05, 2009, 04:46 PM
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ok, got it, thanks krysta. Also thanks for the warning Rodney. Didn't mean to turn this into a science, but there are definitely do-s and don't-s associated with it.

I'm mounting the receiver on the (stampede) front body mounts bracket (plastic) and the antenna tube will be right next to it, so I'll have extra routing length that won't be used (no I'm not going to cut), but sounds like a large coiling is possible. The pic of this guy's coax curves give me the idea of the diameter of coiling I could go with and should work without affecting the integrity of the coax.

http://monster.traxxas.com/showpost....&postcount=116
http://i181.photobucket.com/albums/x.../P1050108B.jpg

Interestingly though, the coax is "trapped" between two pieces (foam) as it exits the rec container to maintain waterproofing. Guess the foam is soft enough not to be a big deal (ie not crush the coax).
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