home *** CD-ROM | disk | FTP | other *** search
- Newsgroups: rec.models.rc
- Path: sparky!uunet!stanford.edu!leland.Stanford.EDU!calvin!zimmer
- From: zimmer@calvin.stanford.edu (Andrew Zimmerman)
- Subject: Re: Crystals AM & FM: Factory Adjustment???
- Message-ID: <1992Jul25.085523.15647@leland.Stanford.EDU>
- Sender: news@leland.Stanford.EDU (Mr News)
- Organization: Stanford University
- References: <1992Jul23.115921.4298@lmpsbbs.comm.mot.com> <1992Jul23.222724.6449@informix.com> <1992Jul24.112417.13418@lmpsbbs.comm.mot.com>
- Date: Sat, 25 Jul 92 08:55:23 GMT
- Lines: 89
-
- In article <1992Jul24.112417.13418@lmpsbbs.comm.mot.com> bobwo@ecs.comm.mot.com (Bob Woodhouse) writes:
- >In article <1992Jul23.222724.6449@informix.com> robertw@informix.com (Robert Weinberg) writes:
- >>Here's another question you R/C gurus can answer while we are on this thread.
- >>
- >>My Futaba radio kit literature (Attack 4-channel AM) says I can buy another set
- >>of crystals, but I'd better send the set back to Futaba for them to adjust the
- >>crystals. True? Why?
- >>
- >>--
- >>+==============================+===============================+
- >>| Rob Weinberg | Workstation publications tech |
- >>| Email : robertw@informix.com | Graphic designer |
- >>| Voice : 415-926-6754 | <imagine your ad here> |
- >>+==============================+===============================+
- >
- >My Magnum Sport instructions said the same thing. Well, it's not quite
- >the case that they would actually adjust the crystals; perhaps they
- >are implying that the would tune some circuitry or something. At any
- >rate, the common and effective practice of just pulling out crystal#1
- >and substituting crystal#2 seems to have given nary a problem to me
- >and to any racers who find that they need to use an alternate frequency
- >in an A-main due to conflict with another racer. In short, I personally
- >would disregard this particular Futabian instruction.
- >
- >Regarding my earlier post which asked if AM and FM crystals are the same
- >thing with different prices, if I ever get an FM radio, I will certainly
- >try 'AM' crystals before I pay the 'FM' crytstal price.
- >
- >Stay tuned,
- >Bob Woodhouse
-
- Futaba might just be protecting themselves by telling you to send it back to
- the factory. The FCC has different rules and regulations for each frequency
- band in the the spectrum.
- For example:
- 53 MHz band - This band can be used by Amateur radio operators for
- radio control. Output power must be under 1 watt, and the amateur's
- call sign, name, and address must be on the transmitter.
- 72 & 75 Mhz band - We don't need a special license to operator on these
- bands, but you do need a license to work on the transmitters. Changing
- the crystals is working on the transmitter. (The Futaba manual mentions
- that it is illegal to change the crystals on these frequencies.)
- Some of the new radios get around this problem by having radio modules.
- Since you are not working on the transmitter, you can change frequencies
- by changing the radio transmitter module and the crystal in the reciever.
- 27 Mhz band - It appears to be legal to change the crystals in this
- frequency band. (Futaba doesn't mention that it is illegal, so I am guessing
- that it is legal.)
-
- FM vs AM crystals - I doubt that AM crystals will work in an FM radio.
- I would guess that they use a different IF. AM typically use
- 455 kHz. FM typically uses 10.7 Mhz.
- I've seen some schematics for recievers that use the 455 kHz for AM. The
- FM IF is based on other radio circuits, not RC circuits.
-
- High cost of crystals and tuning the reciever - National makes IC's for
- both RC transmitters and receivers. In the section on Reciever Alignment,
- they state:
- This is because the crystals which are commonly used with these systems
- may have tolerances as loose as +/- 0.01%. At 49 MHz the resultant +/-
- 5 kHz deviation could easily put the incomming signal out of the 3.2 kHz
- receiver IF bandpass.
- Therefore, there may be some argument that you would like to have the
- reciever factory tuned for a particular crystal. (This would especially
- true for aircraft.)
- It might also explain why the crystals are expensive. ie they might
- have tighter tolernences then those mentioned above. (Or, the radio
- companies want to make a lot of money. :-))
-
- Futaba vs Airtronic crystals - It appears that Futaba and Airtronic
- use the same Frequency crystals for their transmiters (no surprise there)
- and different frequnecies for thier recievers. Why you buy a set of
- crystals, but the set that matches the type of reciever you are using.
- This also means that you can use a Futaba transmitter with an Airtronic
- reciever or vis versa. (I have tried Futaba Transmitter with an
- Airtronic receiver and an Airtronic transmitter with a Novak Futaba J
- reciever. Both worked fine.)
-
- Hope this helps,
- Andrew
- zimmer@calvin.stanford.edu
-
-
-
-
-
-
-
-
-