Changing Frequencies.....danger??
F3AFlyer7 at comcast.net
F3AFlyer7 at comcast.net
Sat Jul 2 17:02:40 AKDT 2005
Thanks for all the help everyone....definitely answered my question!
Scott
> Date sent: Fri, 01 Jul 2005 21:07:56 -0400
> From: Bill Glaze <billglaze at triad.rr.com>
> Subject: Re: Changing Frequencies.....danger??
> To: discussion at nsrca.org
> Send reply to: discussion at nsrca.org
>
>
> After trying to resolve some problems I was having with my 50 MHz stuff, I
> talked to
> some of the JR techs at Horizon and they admitted that the modules are center
> tuned at the factory and that the crystals are then added. Evidently the
> circuitry in
> the module must be tight enough to allow for the variation from one end of the
> band
> to the other. There is no way to differentiated one module from another with the
> crystal removed, either. This may or may not be true for other brands.
>
> Lonnie Misner
>
> > Ed:
> > Good explanation. To those folks that are asking why the crystal is so
> > easily available if it's not to be changed, all I can offer is an
> > explanation that was given me by Tony Stillman several years ago.
> > He said that, as the transmitters and receivers travel down the assembly
> > line, they are, at one point, without crystals. As orders develop, and
> > as different frequencies are needed, the production workers insert the
> > proper crystals into the (otherwise) unfinished radios, to satisfy
> > orders which they have received. (Presumably from wholesalers, etc.)
> > Obviously, they want this production step to be as quick and easy as
> > possible. I assume that then, (and this is a large assumption) the
> > transmitters and receivers are scoped and checked for proper operation.
> > Tony didn't mention this, so I have no verification of that statement.
> > Of course, that doesn't satisfy the question: why are spare crystals
> > available for public sale? As I understand it, even if you have a
> > "lazy" crystal, or a non-working crystal, it is still not within the
> > owners purview to change it. Apparently, however, the FCC considers
> > these infractions not serious enough to spend their enforcement time
> > going after the "offenders." At least, so far.
> >
> > Bill Glaze
> > KI4JQW
> >
> >
> > Ed Alt wrote:
> >
> > > This is quite possibly incorrect. Depending on how it has been
> > > designed, it may not legal or advisable to change crystals in a module
> > > unless you are FCC certified to do so and have the equipment to assure
> > > that the transmitted energy is within spec. Think of it: the reason
> > > we have modules is because you're suppose to swap the module, not the
> > > crystal. Ofcourse it "works" to swap a crystal. All this proves is
> > > that you didn't break anything important when you broke the potting
> > > seal that you usually find on the crystal. This potting seal is there
> > > to tell the bench technician whether you've been tampering with the
> > > module.
> > >
> > > When you swap crystals, you run the risk of transmitting with less
> > > than peak power on your channel, thus wasting energy that would
> > > normally radiate out of the antenna and instead heating the module's
> > > components more than normal. You also run the risk of transmittnig
> > > above legal levels of RF energy elsewhere, in other words, you may
> > > contribute to interference on other channels. You have to realize
> > > that you never get a completely clean signal just on your channel when
> > > you operate your transmitter. Part of the procedure of producing an
> > > RF module includes tuning, or more correctly, aligning the tuned
> > > circuits in the module to the center frequency you want to transmit on
> > > and bringing the unwanted byproducts down to acceptable levels. When
> > > you swap crystals on your own, you have undone this work, at least a
> > > little bit, maybe by an unacceptable amount. Depends on how broadly
> > > tuned the module is designed to be in the first place.
> > >
> > > Why does a synthesised RF module work? It's designed with a tightly
> > > controlled feedback loop to lock onto the desired frequency and
> > > maintain other unwanted RF energy well below specified levels. Why
> > > does it work to swap crystals in receivers? Because the front ends
> > > are broadly enough tuned to allow energy to be received efficiently
> > > within a specified pass band, in our case usually much of the 72 mhz
> > > band. The fine tuning, i.e. what makes our receivers highly selective
> > > to the channel we want is mostly accomplished by circuitry that is
> > > past the stage of the front end.
> > >
> > > Ed
> > >
> > >
> > >
> > >
> > > ----- Original Message ----- From: "Ed White" <edvwhite at yahoo.com>
> > > To: <discussion at nsrca.org>
> > > Sent: Wednesday, June 29, 2005 11:16 PM
> > > Subject: RE: Changing Frequencies.....danger??
> > >
> > >
> > >> I've done this (flown on chan 16 and 29 on 72 MHz and
> > >> chan 00 on 50 MHz) and done this with both my Futaba
> > >> Super 7 and 8UA transmitters with no problem. The 9C
> > >> uses the same module. You can do this freely and
> > >> legally. This is not the same as changing a crystal
> > >> in the transmitter. To the FCC what we call the
> > >> module they consider the entire transmitter, except
> > >> for antenna.
> > >>
> > >> But Steve is absolutely correct, the receiver is a
> > >> completely different matter.
> > >>
> > >> --- RC Steve Sterling <rcsteve at tcrcm.org> wrote:
> > >>
> > >>> No problem in a 9C. That module in the back that you
> > >>> swap to change
> > >>> frequency is a self contained module, no RF parts in
> > >>> the rest of the
> > >>> transmitter (except the antenna I guess). You can
> > >>> even switch to 6 meters
> > >>> which is 20 mhz away.
> > >>>
> > >>> Receiver is a completely different story.
> > >>>
> > >>> -----Original Message-----
> > >>> From: discussion-request at nsrca.org
> > >>> [mailto:discussion-request at nsrca.org]On Behalf Of
> > >>> F3AFlyer7 at comcast.net
> > >>> Sent: Wednesday, June 29, 2005 5:41 PM
> > >>> To: discussion at nsrca.org
> > >>> Subject: Changing Frequencies.....danger??
> > >>>
> > >>>
> > >>> Well I've heard a couple of opinions on this so I
> > >>> figure I'd get some more.
> > >>> I need to get a new frequency for the NATS but don't
> > >>> want to send my
> > >>> transmitter in. I have a Futaba 9C. Some have told
> > >>> me that I can change as
> > >>> many frequencies as I want without mishap, while
> > >>> others have told me that
> > >>> you can only go 6 up or 6 down or else your transmit
> > >>> range gets shorter. Is
> > >>> this true for transmitters with crystals in them
> > >>> only, or for both crystal
> > >>> and module transmitters? If this is also true for
> > >>> module transmitters, then
> > >>> why are there synthesized modules for the 9C?
> > >>>
> > >>> Thanks!
> > >>>
> > >>> Scott
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