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HelicopterMain Discussion › old fm radios
11-22-2017 12:16 AM  20 days agoPost 21
ICUR1-2

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Ottawa, Ontario

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Couldn't a coded signal be used in fm similar to the protcals of today.
or is the fm bandwidth not fast enough to communicate the coded signals.

spending time, paying attention

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11-22-2017 02:00 AM  20 days agoPost 22
EEngineer

rrProfessor

TX

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Hill was using AM....so what? Maybe I also should have said optical enhancement technique so no "nitpicking" about telescope vs binoculars....jeez.

2.4 GHz is just the frequency band used today....

You're conflagrating two different things....

Spread spectrum can and is used with other frequency bands....like UHF, etc....GPS uses "spread spectrum" on two different frequency bands.

And there are many types of "spread spectrum" techniques.

The facepalm can be left at HF where it belongs.....LOL

BTW, with AM transmission, half of the TX output power is used simply to send the "carrier" which sends no info....the other half is split into the upper and lower sidebands, each of which has 1/4 of the carrier's power.

Not the case with FM.

Logo 600SXs, 800XX, TDR IIs

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11-22-2017 03:54 AM  20 days agoPost 23
eyeflyhelis

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charlotte nc

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i only switched back in the day because of noise in the 450 helis. i never had an issues with gas or nitro, that was before large electric helis were popular

only you have the power to make no difference!

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11-22-2017 08:31 AM  20 days agoPost 24
Pistol Pete

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Seffner, FL

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jharkin
FM works just fine on gas. I flew FM and PCM on gas airplanes for years and years... never had a single problem so long as you know how to properly isolate the receiver from the ignition.
My issue was with my gasser heli. It glitched and going to SPCM helped. (JR8103 & Radical 20) Unlike a plane, there isn't a whole lot of real estate to separate electronics and cables as far away as possible from the "sparky" end of the engine.

~~Enjoying the hobby one flight at a time~~

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11-22-2017 12:43 PM  20 days agoPost 25
Dyehard

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Cedar Bluff, Va.

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Maynard Hill's last altitude record was set on September 3, 1970. The actual altitude reached was 26,990 feet. I recall reading with great interest the article on that in MAN, as well as his other record flights when they happened. One item of interest, on the way down, radar lock on the plane was lost and they lost it through the telescope as well. I could be wrong, but I think I remember that he put it in a spin to bring in down. It was down to only a few thousand feet when they spotted it and then only because it was covered in mylar film and someone on the team saw the sun reflecting as flashes on the film, well away from where they expected the plane to be. This was before Monokote. Maynard Hill was an exceptional modeler, there have been and probably will be few like him.

Allen Dye

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11-22-2017 04:19 PM  20 days agoPost 26
EEngineer

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TX

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Maynard Hill was legendary.

A true pioneer of model aircraft and radio control almost before the invention of ICs.

He also made an auto pilot system for RC aircraft.

Logo 600SXs, 800XX, TDR IIs

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11-22-2017 04:45 PM  20 days agoPost 27
w8qz

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Grand Rapids, MI - USA

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ICUR1-2
Couldn't a coded signal be used in fm similar to the protcals of today.
That is essentially what is known as 'PCM', although without the 'bind' aspect. However at 72 MHz the allowable bandwidth is quite limited, compared to what is allowed at 2.4 GHz.

"The helicopter is much easier to design than the aeroplane, but is worthless when done."

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11-22-2017 05:21 PM  20 days agoPost 28
EEngineer

rrProfessor

TX

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In addition to the fact that since the 90's, RF technology has advanced so rapidly...it's astounding.

So we are all reaping the benefits of this....

Frequency pins are a relic of the past....dinosaurs....fossils, even.

Logo 600SXs, 800XX, TDR IIs

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11-23-2017 01:36 PM  19 days agoPost 29
jschenck

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La Vista, NE.

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really too bad that our hobby/industry didn't adopt the DSS protocols into our existing dedicated 72Mhz radio frequencies. I'm sure that at this point the FCC is looking at a reclamation process to get that valuable spectrum out of our hands. Missed opportunity on our side.

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11-23-2017 02:41 PM  19 days agoPost 30
Four Stroker

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Atlanta

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Gassers never worked with the JR single conversion receiver with the gray crystals. The solution was always to go with the dual conversion receiver which had the red crystals (plastic distinguishing cover). The dual conversion worked fine. EE, I am not saying that dual conversion was the solution but that the dual conversion receiver worked and the single conversion one did not.

Just because you are not getting glitched with 2.4 does not mean you are not losing packets. CRC's work, generally. I worked out that a few bad packets an hour can get through with a 16 bit CRC. I don't think people notice a 10 ms glitch.

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11-23-2017 04:30 PM  19 days agoPost 31
EEngineer

rrProfessor

TX

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I had the single conversion JR system....a JR10X.

Worked OK with plank engines....wasn't into helis then.

For the benefit of others, dual conversion would 1st "down convert" the received signal by "mixing" it(RF multiplication) with a 10.7 MHz oscillator....and then filtering the resulting signal.

Then, for the 2nd conversion, a 455KHz oscillator would be used to "down convert" the 1st stage signal....and filtered.

Then the data for the servos would be "extracted" and used to control them.

Back then, without attaching all sorts of cumbersome electronic test equipment to the whole setup, there wasn't any way to see what transmitted info was dropped.

So...if you felt "glitches" when flying, something bad was about to happen.

Land quickly!....

Logo 600SXs, 800XX, TDR IIs

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11-26-2017 12:37 AM  16 days agoPost 32
Four Stroker

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Atlanta

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The 72 MHz frequencies are used in the construction industry. They were always more important that the entire RC community. Antennas at 72 MHz are inconvenient. I don't think anyone in particular wants those frequencies. Otherwise the FCC would have auctioned them off. If you tune a scanner to 72 MHz you won't hear much. I flew on 72 MHz for 40 years without a glitch.

There is not enough spectrum on 72 MHz for modern SS techniques. FASST or DMSS is 3 MHz bandwidth - on each hop - and the 72 MHz band is only about 1 MHz.

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11-26-2017 03:07 PM  16 days agoPost 33
eyeflyhelis

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charlotte nc

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i flew gassers with the grey jr rx crystal, never noticed any issues, but i didn't do any hard flying back then. lost more gasser helis to stripped tail gears that glitches. i also ran all my antennas on a plastic tube coiled up, not sure if that helped but it seemed to work.

only you have the power to make no difference!

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11-26-2017 07:13 PM  16 days agoPost 34
Four Stroker

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Atlanta

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We had 5 guys with gassers that switched to the dual conversion RX and fixed their problems with glitches. Nobody flying Futaba which had all dual conversion RX's had their problem. Plane guys had no problems with the single conversion JR.

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HelicopterMain Discussion › old fm radios
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