I put a FMA crystal in a Hitac r/x in my hand launch today, I experienced no
problems. I did not get a lot of altitude due to overcast and a little
drizzle, I do know I reached at least 87 FEET :-)
Bill
----- Original Message -----
From: "Paul Klissner" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Cc: "Paul Klissner" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Sunday, April 08, 2001 4:30 PM
Subject: [RCSE] Rx Crystal Compatibility ... data, thoughts...
> [EMAIL PROTECTED] wrote:
> >
> > I can't really answer these questions, but I can tell you that Hitec
> > crystals seem to work fine in Futaba receivers, despite what Futaba
says.
> > It would be interesting to know exactly who is mfg these things.
>
>
> So as I start doing some initial research, I have more questions than
answers,
> but a few theories. I think I remember sticking a crystal from
> one brand of Rx into another once and it just didn't work. There was no
> grey area, just <works fine>/<don't work at all>. I haven't seen that
> I know of, and really doubt the <works fine but intermittently fails>
> scenario, unless someone knows for a fact otherwise.
>
> I'll talk to some electronic engineers I know and see if they know the
> scoop. I know that crystals can be driven at their base frequency or
> at an odd multiple or resonant frequency. I would think that a receiver
> would have to be committed to driving the crystal in one particular way
> though, and that could explain the <works fine>/<don't work at all>
> compatibility levels between manufacturers (guessing).
>
> DigiKey (http://www.digikey.com) is a worthwhile electronic component
> manufacturer to know about. They have a big selection of neat stuff,
> at premium prices though... Looking in their catalog, I see several,
> types of crystals listed. They have SMT (Surface Mount) versions which
> are smaller (not what we use) and are more delicate, as well as some
> in more similar larger metal cases.
>
> Here are some characteritic variations I see among them:
>
> Frequency tolerance (in parts-per-million):
> +/- 20 ppm
> +/- 30 ppm
> +/- 50 ppm
> +/- 100 ppm
>
> Aging (degradation of the crystal [first year]):
> +/- 2 ppm
> +/- 3 ppm
> +/- 5 ppm
>
> Maximum Drive level
> 1 uW (SMT package)
> 50 uW (SMT package)
> 100 uW (metal case)
> .5 mW (metal case)
>
> Load capacitance
> 15 pf
> 16 pf
> 18 pf (most common)
>
> Shunt capacitance
> .8pf - 1.7 pf (SMT package)
> 7.0 pf (metal case)
>
>
> Series Resistance:
> 12K - 8K > 100Khz and < 200Khz
>
> I found a nice (brief) online FAQ which defines some terms pertaining
> to cyrstal characteristics. It shows a test circuit [which requires
> both a scope and a frequency counter].
> http://www.timingtechnology.com/crystal_techinfo.htm
>
> >From what I can see at that page, load capacitance is the most
> significant variable in keeping a crystal running at its target
> frequency, and most crystals I saw (esp. in the metal cases)
> have a load capacitance of 18pf.
>
> It would be great if someone could use that test circuit to compare
> manufacturer's crystals. I currently only have a scope, so I can't do
> it at this time. (budget). It would be interesting to learn how
> uniform the Rx crystal playing field is and how many 'black sheep'
> are out there.
>
> I'm sure the receivers are designed around the availability of crystals
> (and NOT the other way around). Further, I would guess that an Rx
> manufacturer's options in crystal selection for a given case-type and
> frequency is somewhat limited to one or two types (crucial question).
> If so, I would imagine that, since R/C aircraft Rx crystals have the
> virtually identical metal case type and share the same frequency
> requirements... (not counting resonant frequencies), that some
> or several RX manufacturers almost certainly using the same kind
> of crystal.
>
> I also believe that receiver vendors are probably committed to long-term
> adherance to particular crystal characteristics, lest a crystal that works
> with one of their units one year fails with another unit the next.
>
> Without suggesting anyone acts on this idea, I have this notion that,
> if a crystal seems to actually work in a receiver and handles a
range-check
> real well, maybe left turned on for long enough to see if it gets "burnt
out,"
> that its characteristics are probably compatible with the receiver, and
> wouldn't just arbitrarily change [this speculation is unverified in
> a controlled experiment or by hard data].
>
> However, the idea that crystals actually age and drift from their base
> frequence is news to me though!
>
> Anyway, I'm flying in the dark here with this, and would love to get
> the facts.
>
> The manufacturers say "Use OUR crystals ONLY!!" Is that a generic
> liability disclaimer, or to help them make a profit, or just
> because there really are one or two incompatibilities
> (and then the question becomes how how black-and-white is compatibility?
> Is it your flying happily for days and then suddenly, due to the crystal
> you run into problems, or does the incompatible crystal just not
> work and its really obvious from the get-go).
>
> I don't recommend that anyone try anything risky or illegal with
> this. I'm just trying to seed some research and collect some data.
>
> -Paul
>
> >
> > At 04:23 AM 4/8/01 -0700, Paul Klissner wrote:
> > >It is fairly common knowledge that manufacturers of
> > >RC receivers strongly recommend that only their brand
> > >of crystals be used with their receivers.
> > >
> > >I'm wondering if that is a question of manufacturers
> > >conservatively and arbitrarily limiting their liability
> > >(on the off chance of incompatibility) or if the risk of
> > >a serious problem is genuinely high? [Not that I'm
> > >advocating taking chances!].
> > >
> > >Is this an issue of FCC rule that manufacturers are following?
> > >
> > >If the risk of crystal/Rx incompatibility is high, can it be
> > >reduced or eliminated by having just a little more information
> > >than the typical uninformed consumer has?
> > >
> > >
> > >More specifically:
> > >
> > > How different *are* the Rx crystals really?
> > >
> > > How many varieties of crystal can there really be in
> > > the common high-profile crystal case? One? Two? Three?
> > > Or something as seriously evil as significant tuning
> > > anomalies which vary from lot to lot?
> > >
> > > Is there a simple test circuit anyone knows about that
> > > can detect differences among crystal batches in the same
> > > case that would affect Rx performance?
> > >
> > > Is there a good way to analyze and deterministically
> > > contrast crystals in an oscilloscope to determine their
> > > compatibility or incompatibility with one another?
> > >
> > >-Paul
> > >RCSE-List facilities provided by Model Airplane News. Send "subscribe"
> > and "unsubscribe" requests to [EMAIL PROTECTED]
> > >
> >
____________________________________________________________________________
> > Brett Jaffee: [EMAIL PROTECTED]
> >
> > Brett's Slope and Power Home Page: http://home.earthlink.net/~jaffee
> > OnTheWay Quake 2 server utility: http://www.planetquake.com/ontheway
> > The Unoffical Extra 300 Home Page:
http://www.bayarea.net/~nathan/extra300/
> >
____________________________________________________________________________
> > RCSE-List facilities provided by Model Airplane News. Send "subscribe"
and "unsubscribe" requests to [EMAIL PROTECTED]
> RCSE-List facilities provided by Model Airplane News. Send "subscribe"
and "unsubscribe" requests to [EMAIL PROTECTED]
>
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and
"unsubscribe" requests to [EMAIL PROTECTED]
