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Home✈️Aircraft🚁Helicoptere-BladeOther › So exactly what crystals will work for the Blade CP and a Futaba 7C?
07-22-2006 02:04 AM  14 years ago
Skiddz

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Carlsbad, CA

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Hmm. I bought a Futaba shorty cyrstal on CH25 and pulled the CH52 crystal from my 4-in-1, changed the modulation on my 9C Tx to PPM and voila! It worked like a charm.A helicopter is 10,000 parts spinning rapidly around an oil leak.
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07-22-2006 08:57 AM  14 years ago
maxchao

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Duluth, GA - USA

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Sorry to interrupt a little bit, can someone explain to me what's the differnce b/w 9C and 7C? I think that's a huge price difference, but both works great right?
If I want a Tx that I can fly BCP as well as a bigger, say .60, gas heli in the future, which one should I get? I just want one I can use for all the helis I will probably get in the future.
Also, does the "module" in the 9C give a way to change the Tx ch w/o replacing the xtal?
and why not many ppl here talk about the Hitecs...
also, get a computer Tx can help me with the tail stability right?
I really know nothing about the computer Tx's...
Thanks for any help!

Josh
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07-22-2006 09:29 AM  14 years ago
Skiddz

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Carlsbad, CA

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As far as I know, the 7CH and the 9CH have the same capabilities (programming-wise) but the 7CH has two less channels. I'm not sure if the 7CH can do both PPM and PCM modulation like the 9C.

The 9C comes with RF modules you can swap in and out to change frequencies. Not sure about the 7CH as I've never seen one up close and personal.

The 7CH will work just fine for pretty much any heli you want to fly. I don't know what the price difference is, but you should be able to score a 9C Tx for less than $300. I bought mine off E-bay for $225 and it had less than 5 total hours on it. It's my 1st computer radio and after the initial learning curve, I find it extremely easy to program.

A computer Tx won't really help you with tail stability unless you want to spend the time setting up revo mixing or you want to "soften" or "tighten" control response with exponential.
A helicopter is 10,000 parts spinning rapidly around an oil leak.
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07-22-2006 02:02 PM  14 years ago
Gary Hoorn

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Annapolis Maryland USA

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As a long time Futaba 7CHP owner/user the differences between that and the 9C are more than just 2 channels. The 9C has many more programming options and a better display. In addition the 7C is a fixed frequency Tx, no modules. That said I have been flying my 7C for about 18 months now in TRex's, Blades, HoneyBees and planes. It works fine, transmits in both PPM and PCM, has all of the Heli mixing you need and enough channels for a nitro heli with governor. It is somewhat limited in the ACRO modes for planes if you need sliders for certain functions. I like the TX and the price is reasonable.

The 7C flies both my Blade and HoneyBee CP2 with the stock 4-in-1 by installing a Futaba Short Single Conversion Crystal on the proper channel allowing all of the Heli functions including mixing!
Gary
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07-22-2006 03:23 PM  14 years ago
stickyfox

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Rochester, NY - US

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I don't know if the horse is dead or not, but let me get a few whacks in just in case...

A crystal is a crystal, when it comes to the tolerances and circuit complexity of RC deisgn. There is no difference between TX and RX crystals. As another user pointed out, there are design specifications other than frequency, but this is only part of the story.

So why won't a TX crystal work in a receiver? It's because the frequency on the label isn't the actual crystal frequency. An RX crystal is at a higher or lower frequency, depending on the design of the radio system. In a single-conversion receiver, the difference is usually 455 kHz. DC receivers add or subtract another 10.7 MHz. Only the TX crystal actually oscillates at the frequency stamped on the case. So if you have a SC channel 30 set, your lane is on 72.390. Your transmitter is operating around 72.390, and your receiver is running at either 71.935 or 72.845. The hobby companies mark the TX and RX so that we don't have to get our calculators out to figure out which crystal goes where.

If you swap the crystals around, your system doesn't work, because the transmitter is now operating on, say, 72.845 (and probably interfering with someone on 52 or 53); while your receiver is listening for someone on 71.935 (which isn't even in the RC band).

It's up to JR or Futaba to decide whether they want to add or subtract 455 kHz, and which load capacitance is best for them, so your best bet is to stick with the original brand or one made for your particular radio. Note also that this frequency difference has nothing to do with transmitter "shift." Shift is an FM property and can be either positive or negative (or both) no matter what kind of receiver you're using.

There's no law against changing crystals. At least, it's not worded like that. Here, we aren't permitted to swap crystals for the above reason, and because changing the frequency of a transmitter may also change the power output, and we're very strictly regulated when it comes to power. If we're already operating at the limit, a few milliwatts could put us over.

The reason Futaba and Horizon make radios with illegal interchangeable crystals is pretty simple. The USA doesn't set the rules for the rest of the world, and as you can see, there are quite a few people flying in Canada and Europe. Americans might be surprised to learn that those Motorola FRS radios you can buy in Wal-Mart require a license to operate at the "5-mile range!" advertised on the package, or that you can buy a CB radio in the USA that transmits over 100 watts despite the legal limit being 12W here (these are made for export to other countries with other limits.) Don't forget we're in a global economy here!

JR radios get around this problem by putting the entire transmitter inside the RF module. You can swap modules because the crystal inside has been tuned and tested to work legally in any transmitter.

It's perfectly legal to put any crystal in a receiver. Put a CB crystal in there if you feel like it. The FCC doesn't restrict the operation of receivers. (There are laws about what you can listen to, though, such as those against eavesdropping on cell phones.)

A ham operator can swap crystals with impunity because his license was issued with the understanding that he is qualified to verify that his transmitter is functioning correctly. If you're licensed to operate on 6m, you can swap crystals in your transmitter. You're also obligated to make sure that you don't cause interference or transmit outside your permission.

I'm a ham operator and a EE, and I know how to test and adjust my E-Flite transmitter, so I'd just as soon save the money and adjust it myself (but you should never assume that just because someone has a degree in electrical engineering they know what they're doing!) I am not the least bit afraid of endangering anyone with my homebrew crystal swap, because I know how to do exactly what the radio tech at Futaba would do. Technically, though, it's illegal because I'm in the States. My ham license does not give me permission to mess with radio equipment on the 72 MHz band. There's nobody going around checking sales receipts to make sure you didn't tamper with your crystals.

But should you modify your radio illegally and then injure someone or damage their property, especially someone with a good lawyer, be prepared to have the book thrown at you. It's heavy.

I hope this clears up a little bit of doubt and uncertainty for someone.
-fox
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05-05-2007 06:46 PM  14 years ago
Shredder777

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Riverside, CA - USA

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help with head speed
Hey guys, we are trying to get the head speed higher after switching to our new radios.

What setting did you use or process to get it really high? we are in the HR3 mode and we are flying cpp.
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Home✈️Aircraft🚁Helicoptere-BladeOther › So exactly what crystals will work for the Blade CP and a Futaba 7C?
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