Hitec/Futaba RX Crystals

No - or it didn't work for me.

I tried a Hitec crystal in the Futaba 8-channel FM receiver. (I had one of the Hitec mini 5-channel receivers I wasn't using at the time, so I borrowed its crystal). The range check was poor. I got a Futaba crystal and got 3 times the range. (The original crystal was damaged in a crash.) The receiver has been working for the last 3 years. The Hitec receiver is in a fun-fly, and also working fine.

Your mileage may vary.

-- Mike Norton

Why would you want to mix critical radio system bits and pieces ?

Cheers, Fred McClellan The House Of Balsa Dust

An answer to an earlier query re receivers and crystals = Futaba 72MHz RX are centre tuned to either the low end of the band 72.010 through 72.490 or the high end 72.510 through 72.990. All other Futaba frequencies are centre tuned. see also =

and scroll down full page. Hitec & JR TX & RX are all centre tuned irrespective of the frequency. Note: Sets are received into this country without any crystals so that customer's requested frequency, including 72MHz, are simply plugged into TX,(or Module) and RX, checked for operation to ensure crystals are inserted correctly and sent out to recipient. USA residents report that Xtals on 72 MHz have been interchanged. However, Xtals on 35, 36 & 40 MHz are not interchangeable as per statement above and our own tests in this country.. Hitec Dual Conversion RX crystals on 35.36 & 40MHz have a frequency 10.7MHz ABOVE the nominal frequency whereas Futaba DC RX crystals are 10.7MHz BELOW nominal frequency. Hitec FM TX xtals are cut at half nominal frequency whereas the Futaba FM TX xtals are cut at 1/3 nominal frequency. see further details under the URL's at Alan's Hobby Web Links "XTALS & Piezo - Manufacturers" FWIW the Local xtal manufacturer who supplies major international buyers inc USA, can copy Futaba xtals but has had an 80% failure rate trying to copy the higher spec'd Hitec xtals. Use the brand of xtal relevant to the unit the crystal is being inserted into = Futaba TX use Futaba TX xtal, Hitec Dual conversion RX use a Hitec DC RX xtal., single conversion RX use single conversion AM/FM crystal etc. A correct brand and type of crystal is cheap compared to the cost and labour invested in a model.

regards

Alan T. Alan's Hobby, Model & RC Web Links

A good check is also on the GWS website =

.

regards Alan T.

Alan's Hobby Web Links

"Dr1Driver" wrote in message news: snipped-for-privacy@mb-m18.aol.com...

Good question, Fred. 'Cause the guy I'm buying the RX and crystal from is offering Hitec crystals $3 cheaper than Futaba crystals. And that's why I asked, I wanted to be sure either way. Dr.1 Driver "There's a Hun in the sun!"

Depends on whether you want it to work properly or not.

You're not a natural philosopher, you're a natural idiot...and filtered. Dr.1 Driver "There's a Hun in the sun!"

Its not my fault if you can neither understand nor appreciate a true statement.

See postings by others, saying in more words, precisely the same thing.

I understand a smart ass well enough, though. AND you weren't smart enough to actually answer the question with some FACTS, like other more knowlegeable people here have done. Dr.1 Driver "There's a Hun in the sun!"

Is there a problem with that? FYI, I had too much info in the filter. He's gone now. Dr.1 Driver "There's a Hun in the sun!"

Well, I did it and it works great for me. I put a Hitec DC FM Xstal on channel 22 in a Futaba 7 RDF receiver and the range was better than the Futaba Xtal, which was also a 22.

Your milage may vary. Ron

I guess that you must have filtered out my posts on the subject. Despite all of the posts to the contrary, every time I have tried to use a Hitec crystal in a Futaba receiver, it has worked fine. So, maybe, we have a different definition for truth. If the darn thing oscillates at the right frequency when the crystal is plugged in, it doesn't matter who made the crystal.

Jim - AMA 501383 (remove NOSPAM to reply)

You're still here, James, the Natural Idiot isn't. Dr.1 Driver "There's a Hun in the sun!"

Howver chances are that it will

(i) oscillate at a cpompletely different harmonic (if it is cut for a wildly diffenet loading)

(ii) oscaillate slightly off band (if it is cut for a slightly different loading), This will work, but do you want to be 1/2 channel off tune?

(iii) oscillate the wrong side of the transmitter frequency, if its cut for that, in which case some or all of the pre-mixer filtering may take the reciver out of spec..

(iv) not oscillate at all.

A little knowledge is a dangerous thing. How many crystal oscillators have YOU designed and built and checked out with a frequency counter. How many radios have YOU designed and built?

Read my post again. I was specific to the application.

This is highly unlikely. Even if the cut is to a different harmonic, if it ocillates, it shouldn't be off in the fashion you describe.

Hitec and Futaba both use the same intermediate frequency and shift.

If it doesn't oscillate, it just plain won't work, period.

I do have a frequency counter, I know how to use it, and I have designed and built oscillators for digital circuits. How about you?

Jim - AMA 501383 (remove NOSPAM to reply)

Actually, its very likely indeed. Test with a frequency counter done in the UK on transmitter Xtals from various brands showed precisely this effect.

They all worked correctly in the same brand rrnasmitter. Ther were up to

5khz out in other brands.

Its very easy to pull a crystal off tine by varying the capacitative loading.

Thats how your FM modulation is done.

I've spent many merry hours tuning up crystal oscillators to be spot on tune.

That isn;t teh point. Is teh LO above or blw th eincoming signal?

yes. it seldonm happens unless e.g. you have an oscillator designed with a hi side LO with a crtystal designed to work in a lo side circuit.

Take 35Mhz. With a first IF of 10.7Mhz that puts your LO at either

24.3Mhz or 45.7 Mhz. Its highly unlikely that an Xtal designed for one would work in a circuit tailored for the other, and even if it did, the chances of it being off tune are hugely increased. Not foregtting that in te first case the image is at 13.6 Mhz, and in te second case 56.4 Mhz. If the reciver has image traps, they simply won't work if a hi side Xtal goes into a low side set.

About half a dozen Xtal oscillators, two Xtal Xmitters, and a digitally tuuned reciever from discrete logic way back in 1978.

In short, I am an elecronics engineer, not a digital meccano kit assembler. I understand concepts like capacitance and resitance, and my voltages come in values other than 0 and 5 :-)

Next?

I am a retired computer science type. I have been involved with design of digital systems since they used tubes. Much of what you say may be true. It's just not applicable to the issue we started with. I said that 72Mhz. Hitec receiver crystals have always worked well for me in my Futaba receivers. I stand by my observations. All this stuff about different harmonics and capacitive loading doesn't matter. The oscillators used are very similar in design, and I've never seen reduced range checks as a result of interchaging them. Several hobby shops that I have used don't even sell Futaba crystals. They supply Hitec ones without complaint.

Jim - AMA 501383 (remove NOSPAM to reply)

BUT you have no way of telling if they are in fact slightly off tune. Or teh oher side of the ibncomong frequency altoghether (I suspect the are not) Until you get shot down by the guy on the adjacent channel.

It does.

You wouldn't. That's another point. The passband of the recievers we use is at least 4khz wide, possibly up to 8-9. You won't see range loss with an oscillator 2.5khz off tune. What is important is that you are bang in the middle of it, because its not your lack of range that will get you - its the sudden 25dB better response to a pager on the next half channel.

our pasband is ideally mesa shaped. with a flat top and steep sides. You want YOUR transmitter in the middle of the flat top, and the other interfering transmitter way down in the valley. Move the whole mesa, and whilst your signal is still on the hilltop, the next door channel may be halfway up the side of the hill, or worse, depending on how good the receiver is.

In teh case of Hitec and futaba recievres, on SC, yes, on 35Mhz they are reasonably interchangeable. I can't answer for 72Mhz.

BUT the REAL point is that just because it seems to work and the range is there, is NO GUARANTEE that they are spot on the right frequency.

Only a frequency countre will show that, and tests have been carried out at the least in transmitters, that show that in general manfacturers crystals are NOT identical.

It would be nice if the bandpass filters actually did what you say. Perhaps, they do to some extent near the center of the band. But, at the high or low end, you have less margin. On 72 MHz., Futaba actually tunes for upper and lower halves of the band.

So, all of this thread was acedemic. You state that you know that Hitec and Futaba crystals are reasonably interchangeable on 35 MHz. But, you argue, without any data at all, that they might not be on 72 MHz.

Is it really likely that range would be unaffected by having an off- frequency receiver? Not with the bandpass filters used by Futaba.

OK, I've just moved, and my frequency counter is packed in a box somewhere. But, I'll try to see what difference interchanging the crystals that I have on the same channels to see what the difference is. The only way to put this to rest is with hard data. All of the data that I do have supports my contention, but if it will help, I will check.

Jim - AMA 501383 (remove NOSPAM to reply)

You are confusing the pre mixer RF filtering with the IF filtering.

You use DC almost exclusively. We use a lot of SC sets. The two situatins are far from comparable.

Yes, it is. And the upper/lower stuff applies to the RF tuning before the mixer. Look up superhet theory.

The only test yu can reaosnably do without a frequency counter is to get a pair of transmitters one on each channel above and below yours, and range check with them. If the crystal is off tune, your reciever will be far more sensitive to one of them than the other.

That is ALL the difference you will notice.