Twisted Sticks May Newsletter

Well we live in interesting times.  Look at what's available for transmitters!  2.4 GHz spread frequency by Spektrum/JR, Futaba and XtremeLink.  It wasn't that long ago that buying a synthesized transmitter was a big deal.  Heck it was only last year I bought a Polk Hobbies Tracker III eight channel transmitter.  This I thought was state of the art in that it scans all the 72MHz channels 11 thru 60 frequencies before it will allow me to transmit.  Now with the 2.4 GHz spread frequency transmitters a frequency board should be a thing of the past.  All spread frequency transmitters claim no more shoot downs due to another transmitter using the same channel!

URLs
http://www.spektrumrc.com/
http://www.xtremepowersystems.net/xtremelink.php
http://2.4gigahertz.com/
http://www.horizonhobby.com/Stores/Products.aspx?StoreCatID=R&SearchTerm=DSM&Page=3


It is interesting that Barry has purchased a new Spektrum DX7.  This means as a club we can gang up on Barry and ask his first hand opinion of it.  Actually I just like the idea of ganging up on Barry period.  J

In my work I've used spread frequency modems since 1999.  These have proven very, very reliable.  Spread frequency modems operate on the same principle that Futaba and XtremeLink uses.  That is they continually changes frequencies as they operates.  The Spektrum and identical JR units as I understand it find two open frequencies and then use these.  In my opinion I like the frequency hopping scheme better as it eliminates the possibility of interference occurring. 

The Spektrum/JR and Futaba receivers use two antennas to eliminate multipathing problems that occurred with one RX antenna.  Spektrum worked for years on this and could not find a solution that would allow one antenna for reliable reception. This article by Cisco (who have a bit of experience in this area) would be useful to review: http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml  XtremeLink claims their system works.  They have had some teething problems with the JR modules they sold at Toledo.  It's way too early to tell.  In most respects they claim to have a superior product.  Notice I said claim.

Spectrum and XtremeLink have transmitter modules for the big name transmitters that use a frequency module.  Naturally the Polk transmitter I have is not one those.  J  All you do is unplug your present frequency module and snap in the 2.4 GHz module which is complete complete with antenna.  Unscrew the 72 MHz antenna and you are ready to bind your receiver to your transmitter.  A receiver that is bound to a particular transmitter will not respond to any other transmitter.  All spread frequency transmitters bind their respective receivers to the transmitter.

This should be very interesting to see how it unfolds as none of the systems are compatible with each other.  So far the question of different systems interfering with each other it has not been definitively answered, but it appears that they do not. 

These systems sound great --- like a panacea to all our problems.  Naturally I'm going to tell you they are not.  You can still have battery problems, bad switches etc.  All these systems are very sensitive to battery voltage dropouts.  If you have a 600 MAh pack with normal wire and a standard switch plus digital servos you could create a momentary drop out of voltage that will cause the receiver to need to re-sync.  This delay is very minor with single frequency crystal controlled 72Mhz receiver but a substantial amount of time is required for a spread frequency receiver to re-acquire its signal.  For what it's worth I'd use twin packs with twin switches plugged into separate ports on the receiver.  This combination lowers the impedance of the power supply by half and provides some redundancy as well.

Performance should be more than adequate for anybody at the club using any of the new transmitters.  After all I don't know anyone who is in the club who is in the professional class.  J  From what I've read the response of these new systems should be better than the 72MHz systems we are used to. 

Some systems claim to be a lot better than others etc.  For those of you who are going to use these specifications to select a transmitter I have a question.  Can you tell the difference between a bushing 3 pole servo and a coreless servo?  How about the difference between a digital and a coreless?  If you can you might be able to perceive the difference between manufactures.

So what would I recommend?  So far I like the Futaba system but it's way too early to tell.  Perhaps a better question would be is if I plan on buying any of these transmitters in the near future.  No I don't, the reason is that in the short five years I've been flying I've never been shot down or had a radio glitch.  Brain glitch yes, something I think was directly related to the transmitters and receiver I use - No. 

If you plan on sticking for the foreseeable future with 72Mhz there are some great deals on transmitters on RCU from the early adopters of the spread frequency transmitters.  On the other hand if you plan on buying new I'd really suggest you take a look at the new offerings.

Have fun flying. 

The next meeting should be at the field weather permitting.  7PM May 10th.