Xtls

[ross blackwell]

I have been collecting Xtls since I first stated flying with A M radio a long time ago but now with 2.4Gig & F M there's some confusion with "matching" Xtls: typically my green tagged 36.370 RX does not whant to "talk" to my green tagged TX 36.70 Xtl ? There seems to be a "oils ain't oils" condition here somewhere. Is there a simple rule of thumb to be aware of here. Apart from not swapping Xtls around which we have all done.

[Andy Gates]

Oh boy what a question.

In a nutshell all crystals are different.

Each manufacturer uses their own crystals or state which brand to use.

Also single conversion and dual conversion reciever crystals are not cross compatible.

Lastly, why would you expect a 36.370 to match with a 36.70, unless it is a typo.

So go through your box of crystals and get them sorted into brand and type.

Futaba single conversion reciever are normally white labelled.

Hitec single conversion reciever have a black end of the label.

Hitec dual conversion reciever have a blue end of the label.

Hope this helps

[ross blackwell]

Thanks Andy, I suspect its the "colour coding" that may have me confused:I have red,green yellow & black. My oldest F M radio is a Hitec with a removable module (Xtal within) & my youngest is also a Hitec.Didn't know much about the "dual conversion" : some of the Xtals have lost the coloured tab off the end through handling but the No's are still legable. I also have a Corona dual conversion Rx that (RP6D1) I can't get to co-operate. Have previously had one working O K If the end coloured tab has gone is there any way of determining the "modus operandus" of a Xtal? By the way,the quoted No's were both 36.370. My key board misses whole words occasionally. Of course I should check before posting.

[ross blackwell]

P S. You only mention Rx colours? does that mean the Tx is or can be different> Keep up the good work.

[John Muir]

Hi Ross,

If the identifying label has come off a crystal so you don't know the make or whether it is dual or single conversion, then I'd throw it away. There's no way I know of to find out what it is without the label. As Andy said, the crystal must be the right type for the receiver or it either won't work at all, or worse, won't work properly and could let you down in flight. For instance, that Corona receiver needs a half size mini dual conversion crystal to work, made by Corona. Some receivers may be designed to use, say, a Futaba crystal, if the maker doesn't do their own, but that would be stated in the spec. Also some manufacturers make crystals to the same spec as Futaba or whatever, but again that would be made clear. If you don't know for sure what you've got, don't risk it. Buy another.

Transmitters are even more fussy than receivers and must never be used with the wrong crystal. Each manufacturer specifies that their crystals are 'tuned' in a specific way and messing about with different makes is courting disaster.

HTH, John.

[John Muir]

Just re-reading your original post, is it that your transmitter and receiver used to work fine, but now don't? If so, then you may have a damaged crystal, or some other failure in the receiver or in the wires taking power to the receiver or a dodgy switch, ESC or any number of things really. What happened to make you think you had a crystal related problem?

John.

[Colin Bernard]

Hi Ross,

Just to echo the comments that without labels it is a challenge, and it may be easier to buy a new set of matching xtals, but often xtals do have their freq's engraved on them, so it is a case of then matching Rx to Tx and deciding whether single or dual conversion xtals are required. If my basic understanding is correct single conversion xtals will be 455 KHz from the Tx xtal and dual conversion typically 10.7 MHz away (although this could vary according to brand).

Your Rx documentation should tell you what is required as it is this end that is affected. Your Tx xtal will always be one of the colinfrequencies, but a dual conversion Rx will need a different Xtal to allow for the way these receivers work. I won't get technical here, but a good write up is here.

You mention the Corona RP6D1 and this is actually a synthesised Rx and so as you know does not require any crystals. I have had a number of the 8 channel versions of these and once tied to a particular frequency have found them very good with excellent range - but I did find problems getting them into the 'search' mode - usually because I was misinterpreting the LED flashes and where I was in the set up cycle, so I would simply perservere here. The default instructions are not that user friendly, so I do have simpler ones. I can't see a way to attach files here but if you want a copy, PM PM me with your email address and I will shoot them over.

[ross blackwell]

P S John,to answer your question; I was trying to set up another model by using a spare Rx I had which didn't already have a Xtal. So I figured by just finding another Rx Xtal everything would be fine. So far the story has been more than interesting.

[Peter Beeney]

I’ve never been quite sure about all this crystal stuff either. I think I would be inclined to think that all crystals are actually all the same, for instance, all transmitter crystals labelled Channel 65 transmit exactly on 35.050 MHz. If they didn’t, surely they would soon be wandering off into neighbouring channels, there is only 10 kHz separation, that is not a very wide band spacing. (For a toy radio.) Likewise with the receiver. Only just a few kilohertz off tune and the receiver might soon be responding to things it might not like.

I bought a Realistic scanning radio in the early 80’s, from Tandy’s, it was a mite expensive, but it was the only one that covered the 35 MHz bandwidth, to check on interference; which I always found to be nil, and a MPX transmitter in the 90’s, which also has an inbuilt scanner so for me it’s easy to check frequencies. I was given a tx crystal once, labelled 62, which was a 63, so they can be mis-labelled, but it’s the only one I’ve ever seen. I suspect that with patience and a scanner it may well be possible to sort out unmarked crystals; one way that might work would be to put them in a tx and try. A tx would quickly show up on channel, a receiver might show up something like an IF away. Don’t know about dual conversion, it would require a spot of experimenting.

For quite a few years I flew in a very busy club, I was more or less a full time instructor, and to ensure that we didn’t excessively ‘hog’ other peoples frequencies I had a pair of MPX rocks on ‘my’ frequency, which I simply always used in the student tx and rx. On the basis that I would not be flying whilst instructing. I never had any problems at all with this combination, at least that I can remember. Although I have to say that it was generally Futaba kit that the beginner chose. I still have a trainer that sees frequent service, plus a couple of old Futaba transmitters, and still using these MPX xtals. The last person to appear on 35, way back now, had a GWS budget set, no buddy provision, so we used my receiver crystal in his rx and my transmitters. Perfect! Also they can be mechanically quite strong, this tx crystal has been through the wash, twice, in the top pocket of my shirt, only found when management was doing the ironing. But it never even noticed, other than it now gives a very clean signal.

We had very little crystal trouble over the years, but I do know for certain sure that it is possible, when the transmitter is very close to the receiver, a single conversion crystal will fire up a dual conversion rx. This doesn’t usually happen, but on one occasion a pilot discovered this on take off when his model instantly flipped over; and was broke; and also a pilot had one fail, fortunately on switch-on, so no harm done.

I’ve always found the single conversion receivers to be be more than adequate. I used Skyleader radio, 27 and 35, for a long time, which was immaculate! The Army used model aircraft as target practise, and probably still do, Skyleader supplied the radio kit for this and so I think it was made to to a very high spec. Their 27 AM receivers had 3 IF, (intermediate frequency), stages, which I’m sure contributed greatly to making them bullet proof! (Sorry!). The 10.7 MHz first stage intermediate frequency of a FM dual conversion is to filter out any image frequency interference, it takes it out of the bandwidth range, and because no one transmits on this frequency anyway; the 455 kHz, and occasionally 465 kHz, IF stage filter out any stray waves and wobbles on the crystal frequency.

But does not 35 and it’s crystals appear now to be fast disappearing? With the widespread use of 2.4, which seems to me to be in some cases very low cost, easy to use and so far trouble free operation, 35 must gradually become virtually extinct, surely, perhaps only used from an interest point of view. I must admit, I still use it, I’ve never had the slightest bother and I like my MPX tx. But Graupner now have a nice new model, so if I decide to up-date that might be the way to go. Or perhaps Multiplex’s new Profi tx could be very desirable.

But I’d think that crystals themselves will be around a long time yet. I suspect that virtually everything that needs an accurate clock uses a crystal of some sort. I believe that most are now made from synthetic materials, and will last for 100s, if not 1000s, of years. In fact, I think the life expectancy for many solid state components now is about halfway to infinity!

And just as a point of interest, is ross, the OP, operating in a distant land? Hence being on the 36 MHz waveband?

PB

[ross blackwell]

Mmm! Interestinger & interestinger?Maybe there's a Xtal conspiracy happening? Will file your notes PB & yes a few of us old fellas down here use 36MHz : I have AM / FM / & 2.4(we call it multi skilling) Mind you a lot of people are still trying to reach our distant land eh! Enjoyed watching some of your Olympics.

RB.

[Antiquated]

Crystals are usually made from slabs of quartz, cut to a size and coated with a pair of electrodes. The size and cut from the larger crystal is chosen to have the desired fundamental resonant frequency. However, the actual frequency obtained when the crystal is used in a circuit depends on the circuit type (eg series or parallel), the external load capacitance, and whether the crystal is forced to resonate at its fundamental frequency, or an overtone. The temperature also affects the frequency, but not much compared to a ceramic resonator for example (the poor man's crystal).

So the label on the crystal is showing the frequency obtained in the designed circuit - in another circuit (a different tx or rx say) it may well obtain a different frequency (but unless a different overtone, close to the original frequency). Sometimes this doesn't matter much (say in a computer where the crystal is used simply as a timebase, and being off by a fraction of a percent doesn't matter much), but for radio and time keeping purposes it obviously does.

[Chris Downing]

Hi,

 

I hope this is a suitable topic for this question. I need to identify this crystal.

I have had it stored for some time in a bag along with a new (at the time) Micron Mini receiver I built.

The Micron receiver is a 35MHz type so I assume this crystal in the bag is for this receiver.

However, I can't identify what it is.

 

It is a plain metal can with a clear, silicon-feeling heat-shrink tube around it.

The writing says FCS 73R on one side and 34.6750MHz  IOD W   on the other side.

 

My old RM Digicon transmitter has a channel 73 crystal in it, which going by frequency tables is 35.193MHz.

What relationship does this new crystal have? Is it correct for a channel 73 receiver? Is the receiver crystal always a bit lower than the Tx frequency?

The tables I see do not mention a receiver frequency.

 

 

[Peter Christy]

Channel 73 is 35.130 MHz. 34.675+0.455 (single conversion IF) = 35.130. Therefore the receiver crystal is for channel 73.

 

I don't know where you got 35.193 from! The nearest "standard" frequency to that would be 35.190 (Ch 79).

 

FM transmitter crystals typically work at either half or one third of the intended output frequency, so 17.565 or (less likely) 11.71 MHz. They are, however usually marked up for their intended output frequency, not their actual frequency.

 

In short, you have the right receiver crystal, and ignoring the frequency tables, you should have the right transmitter crystal.

 

If its not working, then more testing / info needed!

 

--

Pete

 

[Robert Cracknell]

Chris

 

You might find that your crystal is a Fleet (FCS = Fleet Control Sytems), 73 being the frequency and R for Rx.

I have some similarly marked.

[RottenRow]

I fully agree with Peter.

 

I would hazard a guess that your crystal was originally for a Fleet radio; FCS73R = Fleet Control Systems 73 Receiver.

 

Micron used to supply either genuine Futaba crystals, or unbranded ones such as yours at a lower price. Both types worked equally well.

 

Brian.

[RottenRow]

Oh just crossed in the post….

[Chris Downing]

Aha!  Thanks chaps.

 

Yes, I made a typo on that Tx frequency. My table does in fact say 35.130 for channel 73.  🙄

 

Great! That explains it. Probably many people don't know about the IF frequency adjustment to give the actual Rx crystal frequency, so  many internet posts don't even mention the Rx being a bit different to the Tx.

I remember reading that my Micron receiver is designed for Fleet, Futaba or Micron branded crystals, so FCS makes sense now.

Probably, I ordered channel 73 specifically when I bought the receiver kit, so it would match my transmitter. Time fuzzes the memory a bit, eh?

Good to have this collection of knowledge across our members!

 

 

 

[Peter Christy]

Just to add, usually the single-conversion receiver crystals are all the same: 3rd overtone, 455KHz below the transmitter frequency. I think at one point one of the early Japanese sets may have used 455 KHz above the Tx frequency, but I'm not sure. This would have the effect of inverting the pulses at the receiver output on an FM system, and stop the decoder working, if used in the wrong receiver.

 

FM transmitter crystals are generally half the required output frequency, BUT may be designed to work with a different capacitive load. It is varying the capacitive load that generates the frequency swing, so using (say) Brand X crystals in a Brand Y transmitter may end up with the Tx being slightly off frequency. It is important to use the specified crystals in an FM transmitter.

 

--

Pete