coro

I am trying to use my Futaba T6EXA transmitter on a Hitec HFS-04MG (Ultra light) 4ch reciever. I took the crystal from my Futaba reciever and placed it in the Hitec reciever. The servos get power, and the little green light comes on on the hitec reciever, but noting responds to the inputs from the transmitter.

Whats the problem? I thought Hitec and Futaba were compatable? or is it just the servos that are interchangeable?

Thanks in advance.

-Coro

FOD MAN

the futaba is negative shift,this receiver is sold in negative or positave shift. check to make sure that it is negative shift as it will not work if positive

CP140

In addition to the "shift" point already raised, I'd be careful about sticking one manufacturer's crystal in another maker's receiver. You could find that it may not work all that well or that you have a reduced range. From what I've read, different manufacturers have different specs for their crystals.

DBCherry

My Feedback: (4)

You can not use crystals from one manufacturer in another's receiver. You can use a Hitec receiver and crystal with a Futaba transmitter, so they are compatible. Crystals are not.
Dennis-

FOD MAN

This is not true as it has been done too many times by many people over the years. hitec and futaba receiver chyrstals are interchangeable. i know many will object but they are compatable

carrellh

There's a good chance the Futaba crystal is dual conversion. The Hitec receiver is single conversion. That might make a difference. You might want to check MAAC or other rules regarding using a Futaba crystal in a Hitec receiver. In the US, the FCC and the AMA frown on this (even though it appears to work perfectly in many cases).

joeb102072

My Feedback: (9)

Theres also the posibility that the recievers, multiplexers are not compatable with the crystal. There are a number of posts and threads on this subject and the conclusion seems to be while there is no actual evidence of this type of incompatability its just not worth the extra couple of bucks for using a Hitec crystal and Futaba RX, or vise versa. Because there are alleged issues of this nature, there are opionions of some of the electronic guru's here on RCU that that say it could very well be the issue.

FOD MAN

chrystals are not duel or single conversion, duel or single conversion is part of the circuitry within the receiver its self.

piper_chuck

My Feedback: (12)

It's just not worth the cost of a receiver crystal ~$10 to risk crashing one's plane, or even worse damaging someone else's property or causing an injury. Regardless of rumors that it might work, don't do it. There are too many variables to blindly say a Futaba crystal could be used in a Hitec receiver. Buy the correct crystal from the receiver manufacturer.

piper_chuck

My Feedback: (12)

My single conversion GWS receivers require a single (specifically NOT dual) conversion GWS crystal. My dual conversion Hitec receivers require a dual (specifically NOT single) conversion Hitec crystal. My dual conversion Futaba receivers require a dual (specifically NOT single) conversion Futaba crystal. There's a reason manufacturers offer both single and dual conversion crystals, they are made different.

carrellh

You know YOUR setup doesn't work right now so the 'compatibility' argument is pretty senseless as far as resolving the problem you are having.

Assuming the transmitter is not the problem:

You can attempt to rule out the crystal from being broken if your Futaba receiver is still around. Put in the crystal, hook up the battery and a servo and see if it works with your transmitter. If yes, you know the crystal is good. If no, either the crystal or receiver is broken.

If the crystal works in the Futaba receiver, that narrows the problem down. Either you have a bad Hitec receiver, or the Futaba crystal is not compatible with the receiver.

Rodney

Fodman, yes you do require different crystals for dual and single conversion receivers, dual conversion is approximately 11MH off the center frequency while single conversion crystals are 455KHz off center frequency. You have confused transmitters with receivers as the same crystal is used in the transmitter for use with either a dual or single conversion receiver.

FOD MAN

Your right, my old mind is slipping. now what were we talking about?? time for my pills and nap.

8178

My Feedback: (17)

This is how it works. Look up your numbered frequency on the AMA website http://www.modelaircraft.org/comp/frequency.htm

Let's say your transmitter numbered frequency is 14. 14 = 72.070 for the transmitted frequency. The receiver crystal frequency on a dual conversion receiver will be 10.7 MHZ below the transmitter frequency or in the case of number 14, the receiver crystal will be 61.370.

Pretty easy!

Volante24

Let me put my 5 cents, since I was trying to save (little) money (and get fun) using similar tricks. First, crystals for dual and single conversions receivers are on totally different frequencies -- they differ by about 10MHz (of 60)! With the receiver crystals nowadays, the frequency marked on them is NOT the frequency this crystal oscillates, but what frequency the receiver will accept with this crystal plugged in.

Now, Futaba and Hitec RX crystals for the same channel DIFFER in the frequency they generate. I found it experimentally using just an ICOM scanner I had. If I recall correctly, the difference was 10kHz -- just half the distance between the channels. So, if you plug Futaba crystal, say for channel 20 into a Hitec receiver (I did this with a dual conversion receiver), you would get the receiver operating on "channel 20-1/2" (or "19-1/2" , do not remember details). If you plug the Hitec crystal in a Futaba receiver, you also get half a channel off, but in the opposite direction.

Since there are no RC transmitters for half-integer channels in the US, this conclusion is difficult to check, but I am ready to bet is is like that.

Crazy? -- I think so. Probably, this roots to the different (second) IF employed by Hitec vs. Furaba. Probably one uses 450 kHz, and another 460kHz -- hence the heterodyne (which utilizes the crystal you plug) has to be on the frequencies differing by the same 10 kHz, to receive the same radio signal.

Unfortunately, the Hitec guy did not respond to my e-mail asking what is the second IF in their receivers, although usually they respond quickly.

Hope this helps. The summary: RX crystals can be different, in one thing -- just their own frequency for a given channel. (Don't be tricked by the ferquency number written on the RX crystals). GWS and Futaba seem to be the same, Hitec differs by 10kHz. I don't know about others.

Nick

BarracudaHockey

My Feedback: (11)

I don't know whether or not the AMA has any "rules" about this but I can tell you for sure the only thing the FCC cares about is transmitters and that they are within specs as far as freqency and power output are concerned, they dont give a lick about recievers, reciever crystal swapping or anything of the like, they dont even care if your setup works or not, just that you are on freqency and at or below the output power level for that band, which if I'm not mistaken is 3/4 of a watt.

dirtybird

My Feedback: (5)

It may be just me but I have been using Hitec crystals in Futaba receivers for years. I also have a Hitec receiver with a Futaba crystal that I have several hundred flights on.

Volante24

Good, This give me another motivation to look at the subject anew, closer. I have dozens of RX crystals made by GWS for Futaba and after that experience decided they were of no use for the Hitec receivers. If you are right, it's better for me.

I had checked though with all the equipment that the TX crystals put into Hitec radio give a wrong frequency, by 10kHz sharp. This was more puzzling since no IF is involved in the transmitters. Since that was already enough I did not study if the modulation
was correct or not. But, actually now I know how to tune Hitec's Lasers, it is not too difficult (once you have a suitable frequency counter), so I guess I would be able to overcome this incompatibility -- should I need this.

Volante24

Just came across on the Web, http://www.torreypinesgulls.org/Radios.htm:

The frequency of the receiver crystal is NOT the channel frequency e.g., the receiver crystal for channel 14 (72.070 MHz) is
NOT 72.070 MHz but displaced by the IF frequency. The exact IF frequency is vendor dependant so DON'T MIX
CRYSTALS FOR DIFFERENT VENDORS. (e.g., don't plug a Futaba crystal into a Hitec receiver and expect it to work.)

hellcat 1

Crystals are cut on a fundamental frequency. Usually that freq. is one 5th or one 7th of the freq that the oscillator is tuned to in the receiver. In othe words the oscillator is operating on a harmonic of the fundamental and on a dual conversion receiver it is offset from the freq. of the transmitter by the freq. of the first IF amp, which is either 10.7 or 10.9 mhz. so the freq the crystal is cut on is 1/5th or 1/7th of about 61.8MHZ. You have to know your exact freq. to get the math right. Some manufacturers use the 5th mode crystal and some use the 7th mode and it will either work or it won't. On a single conversion receiver the freq. is offset by the freq of the 1st IF which is 455KHZ so that crystal woud be cut about aboput 1/5th or 1/7th of a freq that is 455Mhz away from the Transmitter freq. A single converion crystal will not work in a dual coversin receiver and visa-versa. The reason we went to dual conversion receivers was to get away from a problem called image freq. If you were on the right freq a transmitter that was close to 455KHZ away from that transmitter could possibly interfer. Hope this makes everything as clear a mud.

Volante24

Thanks,

I more or less know the general facts, but failed to find the specific information. I believe both Hitec and Futaba use the 5th harmonics. So far,
however nobody answered me which IF's (first and second) are employed by Hitec or Futaba. My guess was that they differ, but in their second IF, by a small amount like 5 or at most 10 KHz. 100 or 200 kHz difference are ruled out, unless the selectivity at the first IR stage is poor. I have an open Electron 6 from Hitec on my desk, and it has one filter marked as W55H (with T below H), I guess from Murata (M embedded in C, something of this sort). Does this mean the second IF is 455 kHz?
Anyway, you mention an interesting fact. If the difference lies in the first IF and it is 100 or 200kHz sharp, one can use the crystals offset by 5 or 10 channels, respectively. That would be an opportunity!

Nick

hellcat 1

The second IF on both radios is 455KHZ but I dont't know about the first IF freq. They use commerical IF transformers and filters and what is available is 10.7MHZ and 10.9MHZ> That would be where the difference could be. You should see another crystal that would be 455MHZ above or below the other freqs. All dual conversions receivers have at least two crystals and some have two crystal filers in them. That's what you are looking at that says w55h. It's a 455Mhz filter.

hellcat 1

That should have been 455KHZ filter. sorry

Volante24

Thanks for clarifications. I have put Electron 6 together and
installed into my son's electric trainer while pulled out the
original Hitec HFD-08RD (aka RCD3500). In between we took close up
pictures of the both, from both sides. The circuits look similar, yet the
standard-size RCD3500 has two obvious quartz crystals build in
(besides the removable one). It seems to me Electron 6, the micro, had
only one such crystal, but I could not read its frequency.

The two crystals of RCD3500 are for 10.7MHz and 11.155MHz. Hence
apparently the first IF is 10.7MHz and the second is the difference of
the two, 455kHz. I wonder how a (quartz) crystal, even on 10MHz can
pass 20 or even 10KHz bandwidth, I thought true quartz crystals have Q
in the range of at least 100000; well, they probably can make them
worse...

If Electron 6 does not have a counterpart of its bigger brother's
pass-through crystal on the first IF then they probably are not quite
the same in their fidelity as marketed by the manufacturer.

How to understand the filter's nature by the marks on them? Do W, H
and T mean something specific?

I have a GWS-for-Futaba DC RX crystal on channel 22 with me, and hope
to check which precisely frequency it oscillates on in the
receiver. This can be compared with the same for the genuine Hitec one
at channel 19 and 33 or 40 I have at hand. This will give a final answer to
the compatibility issue.

By the way, last May I got a reply from Steve Morton at Hitec/Multiplex
Customer Service -- it said the measured frequency for the TX on
channel 20 must be approximately 72.191MHz. Does this make sense if
the frequency for this channels is nominally 72.190MHz and Hitec employs
NEGATIVE shift? Since that time I am trying to find out what, after
all, is the precise carrier frequency and the maximal deviation,
nobody answers as if it were the top secret!

The RF part seems to have three identical coils and one which visually
differs, lower and with differently looking/colored core screw. I
guess the three similar are preselector LC filters. Do you
know what is this fourth one -- is it an image frequency killer, or an
inductance for the first heterodyne, or has something to the second
stage?

Nick

kerwin50

The biggest factor is the Q of the crystal if the Q dosen't match matchthe input impedance of the frist lo then she will not osc at the desired freq, or may not be stable, there are several parmerters a engineer gives to the company that is cutting the crystal just because 2 crystal osc at the same freq dosen't mean they are interchangeable look in the 1985 radio amature handbook for futher details