RunRyder RC
 3  Topic Subscribe
WATCH
 1 page 730 views
Scorpion Power Scorpion Power
Helicopter
e-
Align
Other › 450 xl ccpm
10-08-2005 08:20 PM  12 years agoPost 1
goodfella

rrNovice

Romford, Essex,​England

My Posts: All  Forum  Topic

does anyone know if i need a dual conversion tx crystal as well as a dual conversion rx crystal

i am close to completing my first 450 and my transmitter dosn't seem to be talking to my receiver.

help !!!!!!!!!!!!!!!!!!!!!

PM  EMAIL  Attn:RR  Quote
10-08-2005 08:43 PM  12 years agoPost 2
lsnover

rrVeteran

Lehigh Valley, PA

My Posts: All  Forum  Topic

Most transmitters are dual conversion.

Just some of the lower end recievers are single conversion. Make sure you have the right type of crystal for your reciever.

Regards,
Lee

PM  EMAIL  GALLERY  Attn:RR  Quote
10-08-2005 08:51 PM  12 years agoPost 3
RICHW

rrVeteran

Cupertino, CA

My Posts: All  Forum  Topic

It is of no importance how the transmitter manages to transmit on a particular frequency (unless you are actually changing the crystal itself, and not the module - like Futaba). Transmitters usually contain a lower frequency crystal such as 18.xx mHz and multiply the frequency to get a center frequency of, say, 72.030 mhz. The receiver will not care what was done to get there. The modulation technique IS what matters. PPM vs. PCM and negative shift vs. positive shift. Actually, i still don't understand the latter, completely. But fortunately, everything is marked with an 'F' if it for futaba.

PM  EMAIL  Attn:RR  Quote
10-08-2005 08:59 PM  12 years agoPost 4
dkshema

rrMaster

Cedar Rapids, IA

My Posts: All  Forum  Topic

There is no such thing as a "Dual Conversion" transmitter.

And assuming that was a typo in the earlier response, it's not true that most receivers out there are dual conversion....

Dual conversion refers to the method used in the receiver to detect and amplify the desired signal. If you have a dual conversion receiver, then you need the correct frequency crystal for it. Stick with a crystal from the manufacturer of the RX for the crystal, and make sure the RX crystal is for the dual conversion model.

If you are going to switch crystals in your transmitter, you don't buy a "dual conversion" crystal for it.

And without wanting to start a whole 'nother thread about the FCC and legal stuff -- just beware -- even though you can buy crystals for your transmitter in the United States, the FCC regulations that govern the operation of your transmitter specifically forbids changing the crystal in a transmitting device. There are too many threads here on RR with regard to this practice.

Dave

PM  EMAIL  GALLERY  Attn:RR  Quote
10-08-2005 09:04 PM  12 years agoPost 5
lsnover

rrVeteran

Lehigh Valley, PA

My Posts: All  Forum  Topic

Dave:

Technically you are right, but from a practical standpoint, what I said is true. I.e. the Transmitter works with both types of recievers.

It's primarily the crappy little receivers out there that are single conversion. Most of what we have in RC is dual conversion and has been for years, except for the mini, close range stuff.

Personally, I don't trust single conversion stuff with anything but some real cheap foamies and my Blade CP (because that's what it has). There's just too much glitching with these little recievers.

Cheers!
Lee

PM  EMAIL  GALLERY  Attn:RR  Quote
10-08-2005 09:08 PM  12 years agoPost 6
dkshema

rrMaster

Cedar Rapids, IA

My Posts: All  Forum  Topic

The most common cause of a new receiver not working with an existing transmitter is that the transmitter is set to transmit PCM, and the receiver is not a PCM receiver. This is especially true if the receiver is not the same brand as the transmitter. If your receiver is from a different manufacturer than your transmitter, you need to operate the TX in FM (PPM) mode. The PCM algorithms used by Futaba, Airtronics, HiTec, JR and everyone else are proprietary and unique to the TX manufacturer. Third party receivers don't incorporate the various decoding algorithms for PCM. Switch to FM in your TX and see if this helps.

The second most common cause of a new receiver not working with an existing transmitter is that the RX is of the "wrong shift" type. Essentially, even in the FM world, JR, Futaba, Hitec, and Airtronics defined their FM encoding method differently. The result is two types of shift -- one positive, the other negative. If you are buying a third party receiver to work with your existing transmitter, then you need to make sure the two are using the same shift method. That's why you see Hitec (and other) receivers sold as "positive" or "negative" shift, or for JR and Futaba radios separately.

The third most common cause of a new receiver not working with an existing transmitter is the selection of the wrong type of crystal that will work with the receiver. Read the receiver specs and make sure you bought a crystal that will do the job.

Dave

PM  EMAIL  GALLERY  Attn:RR  Quote
10-08-2005 09:16 PM  12 years agoPost 7
dkshema

rrMaster

Cedar Rapids, IA

My Posts: All  Forum  Topic

I beg to differ that "most" RC receivers are dual conversion. Check how the majority of JR "ABC&W" receivers are designed and have been for the last 20 years or so.

Single conversion and they have all worked absolutely flawlessly all these years. Of the ten or so JR receivers I have in my helis and airplanes, NONE are dual conversion and they have NEVER caused a problem. With regard the Futaba FM receivers I have in some of my aircraft, NONE of them are dual conversion, and they, too, have performed flawlessly.

The only real advantage dual conversion gives you is better image frequency rejection. The dual conversion receiver is not inherently more reliable than a single conversion radio, unless you have a problem with image frequencies.

Dave

PM  EMAIL  GALLERY  Attn:RR  Quote
10-09-2005 01:15 AM  12 years agoPost 8
lsnover

rrVeteran

Lehigh Valley, PA

My Posts: All  Forum  Topic

Well, I beg to differ with you begging to differ.

Unless you have some really old Futaba stuff, almost every receiver they make is dual conversion, same with JR.

As far as you having no problems, you must be flying very close in most of the time. As the single conversion receivers are undoubtedly more prone to glitching and interference.

Other then that your order of common problems is right on.

Another thing to check.... If you have a Futaba Sythn Transmitter module, they do not work properly with many of the third part receivers.

Regards,
Lee

PM  EMAIL  GALLERY  Attn:RR  Quote
10-09-2005 01:48 AM  12 years agoPost 9
ghjr

rrNovice

Byram, MS

My Posts: All  Forum  Topic

dkshema is right, JR has recently offered a couple of dual conversion receivers but for the most part they have all been ABC&W.

PM  EMAIL  Attn:RR  Quote
10-09-2005 02:35 AM  12 years agoPost 10
dkshema

rrMaster

Cedar Rapids, IA

My Posts: All  Forum  Topic

There is no technical reason that a single conversion receiver is more prone to glitching than a dual conversion RX, unless the source is a signal on the image frequency.

Whatever makes it through the passband of the front-end will make it through both conversion stages of a dual-conversion RX, and through the one conversion stage of a single conversion RX. It is the quality of the front-end electronics, prior to any conversion that determines the selectivity of the RX, not the number of heterodyne stages you run it through. As both dual and single conversion receivers must meet the current narrow-band specs to be produced and sold, their performance will be pretty much identical.

Third order intermodulation distortion performance is determined by the quality and design of the mixers used in the RXs, not the number of conversion stages.

If the glitch source is noise is caused by metal to metal contact, or from an ESC in an electric heli, this is usually broad band noise that if it makes it through the front end passband filter of the RX, before any conversion is performed, it will make it to the decoder.

If the source of the noise is an ESC, such as is common with the Phoenix 25/35/45 ESCs, the noise is not getting in through the front end, but is conducted noise on the power, ground, and throttle signal line. As this is dirty power, and noise being injected into the back end of the decoder, a dual conversion receiver will perform no better than a single conversion receiver. And, if the noise is somewhere in the 455 KHz band, it can couple into the IF of any single conversion RX, and into the second IF of a dual conversion RX. In either case, it will make it to the detector and decoder.

The JR ABC&W receivers being single conversion perform exceptionally well, and I'd put them up against any dual conversion RX from any other manufacturer.

Ponder this: If dual-conversion receivers are bullet proof when it comes to glitching, please explain the numerous complaints of glitches when using the HiTec Electron 6 receiver in the T-Rex. This is a modern, dual conversion receiver and unless you filter the power and throttle signal from the ESC, it is nearly impossible to fly one of these in a T-Rex.

BTW -- NO, I DON'T fly close in all the time, I rarely fly close in. Having learned to fly on fixed wing, and having to fit my helis in with the fixed wing flyers at our field, close-in flying is a luxury here. I've used single conversion RXs in helis and airplanes for about the last 30 years. Range HAS NEVER BEEN A PROBLEM, either in helis, or fixed wing, or even sailplanes which one usually NEVER flies in close proximity.

Dave

PM  EMAIL  GALLERY  Attn:RR  Quote
10-09-2005 04:41 AM  12 years agoPost 11
lsnover

rrVeteran

Lehigh Valley, PA

My Posts: All  Forum  Topic

Dave:

I don't know the technical reasons, but I can say without a doubt the single conversion receivers I have tried, have been much more prone to glitching and interference then the dual conversion, especially on electrics. I use the same transmitters in both cases, a Futata 8U and a 9Z.

Maybe JR does a better job here? But I will not run single conversion on anything I care about that I'm going to fly more then a 100ft or so away. I'm new to helis, so maybe more of the heli folks use single conversion. On the Futaba/aircraft side, all I see is dual, with the exception of some of the cheap little receivers being used on electrics.

I will defer to your expertise on what is happening on the technical end. But as far as electrics go, they are more prone to glitching with either type of receiver, due to noise from the motors and ESCs. I don't think this particular type of problem is specific to either type. But the singles I've seen and used have had far less range and far more glitches then the duals I've used.

Glad your experience is better.

Cheers!
Lee

PM  EMAIL  GALLERY  Attn:RR  Quote
10-09-2005 05:49 AM  12 years agoPost 12
dkshema

rrMaster

Cedar Rapids, IA

My Posts: All  Forum  Topic

goodfella --

Sorry your post took that left turn. Hope you got your RX working with your TX. Let us know.

------------

"Cheap" and single conversion are not the same thing, and don't belong in the same sentence. One has nothing to do with the other.

A cheap RX is something like you'd find in a Dragonfly, Hummingbird, Blade, or any of the GWS micros. They are not high performance, not particularly selective, and not particularly sensitive. Those receivers are designed to be cheap, have short range, and in general sell for next to nothing. After all, when you can buy an entire, ready to fly heli such as the Blade with transmitter, receiver, servos, motor, battery, speed control, gyro and mechanics for $200 or so, you can bet there isn't a lot of money tied up in the electronics!

There are very few, if any "cheap" receivers being used in T-Rexs. There are also very few, if any, receivers that don't get glitched in T-Rexs. There have been many dual conversion Hitecs, Futaba, and other brand receivers that glitch just as often and just as bad as single conversion RXs... in almost all cases, you'll see that proper component location and the use of a ferrite toroid (or other form of electrical noise filter) on the ESC to RX cable has cured those glitchy receivers.

Heli flyers are very particular about their radios, after all, none of us wants to dump a heli (whether a T-Rex or a Freya EVO 90) due to bad radios. I have no qualms about using a single conversion RX in ANY kind of aircraft. And I'm pretty sure that I'm not in the minority on that point.

Dave

PM  EMAIL  GALLERY  Attn:RR  Quote
10-09-2005 12:49 PM  12 years agoPost 13
lsnover

rrVeteran

Lehigh Valley, PA

My Posts: All  Forum  Topic

Dave:

I will conceed. ;-)

But my experience has been different.

Hopefully goodfella got enough pointers to find his problem.

Again, maybe JR is different. But I would not run a poor quality/cheap OR single conversion receiver in anything I care much about.

My experienced may be biased in that all of the single conversion recievers I've played with would be considered "cheap" and I have not seen any of the good quality ones you mention.

Have a good one! We're trying to dry out here in Eastern PA, over 9.5" of rain since Friday night! Oy.

Cheers.
Lee

PM  EMAIL  GALLERY  Attn:RR  Quote
10-09-2005 04:22 PM  12 years agoPost 14
Gary Hoorn

rrKey Veteran

Annapolis Maryland​USA

My Posts: All  Forum  Topic

Lee,
Quite a few of us are using the Futaba 146ip PCM Rx which is single conversion in our TRex's. They perform flawlessly. As stated in other posts dual conversion will not filter out locally generated electrical noise in fact dual conversion Rx's can be more prone to distortation due to the abundance of harmonics generated by the crystal having to generate frequencies that are compatible with both the first and second IF stages! These points have been argued ad nausea! Careful design of either type will produce acceptable results.
Gary

PM  EMAIL  Attn:RR  Quote
WATCH
 1 page 730 views
Scorpion Power Scorpion Power
Helicopter
e-
Align
Other › 450 xl ccpm
 Print TOPIC  Make Suggestion 

 3  Topic Subscribe

Saturday, November 18 - 10:20 am - Copyright © 2000-2017 RunRyder   EMAILEnable Cookies

Login Here
 New Subscriptions 
 Buddies Online