what does this mean?

Dual conversion means the receiver has two IF (intermediate frequency) stages vs one (single conversion) What this means is that the reciver can more finely tune in the desired frequency, that of the TX. It helps eliminate noise from close frequencys.

Don

A single conversion receivers a cheaper smaller and lighter and are used in the park flyer type planes They do not have the long range capability of the more expensive receivers. These receivers have a single image frequency conversion and do not have as good adjacent channel rejection as the more expensive receivers

Dual conversion receivers have two image frequency conversion stages and have better adjacent channel rejection

To change the frequency of either type receiver requires only one crystal but a dual crystal cannot be used in a single conversion receiver and vice versa

It means that two intermediary frequencies are used in processing the signal. In a single conversion receiver, only on is used. Basically different design philosophies that produce the same end results.

Your answers are basicly correct however, do not truly apply to JR radios, which are single conversion but make use of another means to provide the same or better signal reception. Of course now with the 2.4 system all has changed.

ok what does shift selectable mean . lee

When buying an 'aftermarket' rx (not an RX offered by JR/Futaba), you can select 'Negative' or 'Positive' to allow the aftermaket RX to work with a particular brand.

I forget which brands use negative and positive for their RX's, but it's documented in the specs.

Hitec and Futaba are negative shift.

JR and Airtronics are positive shift.

A transmitter of either shift will shoot down a plane with a receiver of the opposite shift if turned on

So if some one is flying using JR transmitter and reciever and I turn on my Futaba transmitter, I will interfere with his signal?

If they are on the same channel, yes.

Yes , common sense. Just trying to understand what w8ye ment. He didn't specify same channel.

Yes same channel

Thanks

If you're relatively new to the hobby and shopping for receivers and am not sure what dual conversion means, do yourself a favor and pick up a 2.4 ghz radio. They're virtually foolproof. Learn how to fly, build planes and tune engines. There's no need to fuss with frequency pins at the field anymore.

I guess I'm old school, I, not convinced 2.4 ghz is bullet proof yet. The more that switch over makes my 72 MHz safer to use. Up front cost of some 2.4ghz radios would be great cost of equipment to only find out you didn't like flying.

It appears that the Specktrum 2.4 systems have some teething problems yet?

Today my friend and student hurt his nice new plane with his 2.4 9303 JR. According to Horizon if the cute little antenna isn't bent at 90 degrees or the antenna is pointed directly at the plane they can loose the signal?? Don't ask me, I don't have a clue but I have seen a number of the 2.4s loose signals for a couple of reasons. So far the only real plus I see is not having to use the pin board. 2.4 is not fool proof, just new.

For the same reason you don't want to point your transmitter antenna end at the plane.

They have had several antenna rounds with the new system

The duel conversion receivers do use two intermediate frequencies, 10.7 MHz and 455 KHz. These were picked due to the fact that AM radios used 455 KHz, and FM radios used 10.7 MHz. The older single conversion used 455 KHz only.

Receivers used in RC started using the super-het concept in 1958 when the FCC allowed 6 frequencies that were for the most part 80 KHz apart. At that spacing, it was easy to filter out adjacent frequencies, so single conversion was used. It was not until the early 70's that EK came out with the first dual conversion for RC. EK was also the first to use the bridge amplifier in the servo that allowed two wire batteries, so they contributed quite a bit to the industry.

The super-het (hetrodyne is an ancient term for taking two signals of different frequencies and mixing them in a non-linear circuit) makes all modern receivers possible. This technology takes a fixed frequency from an oscillator, and mixes it with the signal from the antenna and sends the result to a filter that passes just the IF frequency (actually a limited band of frequencies get through). As people already stated, do it twice for dual conversion.

The real problems with receivers has more to do with the filter design, intermodulation distortion, and automatic gain control. The mixing works well if the power levels are controled.

The main advantage of dual conversion is that the image frequency of the first I.F. stage is now easier to filter out at the antenna, since it is now 21.4 MHz away from the pass band of the antenna. So a simple filter with a very low number of poles has an effective filtering effect. With the single conversion at 455 KHz, the image is only 910 KHz out. Note that with all 50 frequencies, that it no longer can keep out the possible frequencies that can be encountered at the average model flying field.

Yes, the JR is single conversion, but they don't operate on all 50 frequencies to avoid image problems.

Very good High Plains

To help in his statements are the fact of harmonics (or Multiples) of frequencies. The old CB radios used to come on channel 5 on your television. They were not on the same frequency but channel 5 on TV was like the third harmonic of channel 19 on the CB.

Harmonics are used in receivers, mostly in the oscillators. It is much easier to make a crystal at half the frequency, then use a tuned circuit after it with a frequency doubler.

I got shot down a very long time ago by a hospital radio working at roughly 146 MHz, because it was very powerful signal, and it mixed down to the IF frequency. The good ole days, the radio lock up with full up, and full aileron until it spiraled down to the parking lot. Kraft built tough equipment, but it couldn't reject 100 Watts from a couple of blocks away.

I keep hearing about this cone of silence. In practice, I don't think its a big deal at the range we fly, though I suppose reciever installation could make it more or less likely.

I've pointed the tip of my 2.4 antenna right at a 2.5m glider that was way WAY up and couldn't force it to loose control or drop a significant number of frames. Your mileage may vary of course, but I just don't think its a big issue.

Unfortunately that doesn't prevent the kid with the walmart or radio shack special from getting out of the car and turning on not knowing any better, where with 2.4 thats no issue.

72 is definately less busy though, IRCHA had 780 pilots and only impounded 43 radios last August.