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single vs. dual conversion receivers

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Old 07-21-2006, 09:22 PM
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barchiola
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Default single vs. dual conversion receivers

hi everyone and thanks for reading my question.
i just bought a hobby lobby esskay pitts foamie and i'm trying to pick a receiver for it. i have a jr xf421ex radio and i don't know if i need to buy a single or dual conversion receiver for it. i'm currently trying to decide between the fma direct encore (dual conversion) sub micro receiver and the hitec micro 05s (single conversion).
i've been in rc on and off for many years but this stuff with lipos's, brushless motors, foamies, etc. is making my head spin trying to make sense of it.
thanks in advance.
bart
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Old 07-22-2006, 12:48 AM
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Default RE: single vs. dual conversion receivers

The Hitec O5S will work admirably in this application. We have extensive in-flight experience with this RX and foamies indoor and outdoors.

The only consideration is the range IMO with micro RX's, dual conversion/single conversion is not an issue. This RX like nearly all Hitec RX's dual and or single conversion are specified at ONE mile plus range...
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Old 07-22-2006, 08:06 AM
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Default RE: single vs. dual conversion receivers

The main advantage of dual conversion is noise rejection. At the range you will be flying its a non issue.
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Old 07-22-2006, 09:14 AM
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Default RE: single vs. dual conversion receivers

thanks guys. what the limit to the size of airplane i can reliably use the fma dual conversion receiver in? can a smaller receiver be used in a larger nitro plane?
thanks
bart
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Old 07-22-2006, 10:08 AM
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Default RE: single vs. dual conversion receivers

Yes, you can use the FMA receiver in a nito plane, all sizes.
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Old 07-22-2006, 10:52 AM
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Default RE: single vs. dual conversion receivers

dual conversion has nothing to do with noise rejection. it is not a consideration in range calculation. single conversion has a vulnerablity to another transmitter at just the right frequency such that a 455 harmonic is generated and is passed thru your receiver. not good . dual conversion recievers with 2 xtals were invented to obviate this vulnerability. jr has a way of taking care of this with single conversion. i believe that when you buy a single conversion receiver you have opened yourself up to that vulnerability. park flyers seem to get away with it but i dont know why.
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Old 07-22-2006, 11:35 AM
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Default RE: single vs. dual conversion receivers


ORIGINAL: barracudahockey

The main advantage of dual conversion is noise rejection. At the range you will be flying its a non issue.
While I agree conceptually, at our level with R/C Receivers this is not an issue with currently available quality SC RX's. JR, Berg, MPX and Schulze have proven this for years; Giant scale thru Parkflyers...

The DC receiver and its inherent ability to offer higher suppression of the image frequencyWAS useful years ago. Components have come along away and with the improvement seen with or of 455 KHz filters and the integration of Microprocessor decoding techniques the importance of same has been become all but moot IMO.

Granted there are some inexpensive SC RX's out there that are less than stellar performers.

If the RX is specified as a FULL range unit and or a mile plus RANGE, it’s all good for your glow powered models.

To ensure you have a viable flight system, as always perform a rigorous range check prior to committing the model to flight.
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Old 07-26-2006, 11:46 PM
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Default RE: single vs. dual conversion receivers

Hitec customer service is first rate!!

FMA customer service is very poor to nill.

Go with Hitec.
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Old 07-27-2006, 10:26 AM
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Default RE: single vs. dual conversion receivers

the stuff i've bought from hitec has always been very good. this is my first order from fma direct so we'll see how it goes. so far though, fma sent me an email saying they'd send another when the items shipped but the box arrived before the email ever did.
go figure.
bart
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Old 07-27-2006, 11:56 AM
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Default RE: single vs. dual conversion receivers


ORIGINAL: laryboy

dual conversion has nothing to do with noise rejection. it is not a consideration in range calculation. single conversion has a vulnerablity to another transmitter at just the right frequency such that a 455 harmonic is generated and is passed thru your receiver. not good . dual conversion recievers with 2 xtals were invented to obviate this vulnerability. jr has a way of taking care of this with single conversion. i believe that when you buy a single conversion receiver you have opened yourself up to that vulnerability. park flyers seem to get away with it but i dont know why.
The image frequency is not a harmonic. A transmitted frequency(fundamental or harmonic) on the image frequency will be received just as well as the desired frequency. It must be rejected in the RF stage and cannot be rejected in the IF or compensated for in the decoder.
Any coded system will work better if it has a double conversion RF stage. Its probably not needed for short range receivers but would make them better if supplied. Thats why all major suppliers use it.(even JR & Hitec)
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Old 07-27-2006, 01:57 PM
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Default RE: single vs. dual conversion receivers

try to think of the question when replying. is there still a vulnerability in single conversion park flyer type receivers ?
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Old 07-27-2006, 03:28 PM
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Default RE: single vs. dual conversion receivers

ORIGINAL: 2fast

Hitec customer service is first rate!!

FMA customer service is very poor to nill.

Go with Hitec.
Hitec's support is certainly legendary (I speak from experience) and I have also had excellent service from FMA although it is sometimes a little patchy.

Both companies however, make first-rate products.
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Old 11-26-2006, 10:31 AM
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Default RE: single vs. dual conversion receivers

You don't know what you are talking about. Dual conversion receivers don't have dual crystals. They have two IF stages and still have a single crystal.
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Old 11-26-2006, 11:11 AM
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Default RE: single vs. dual conversion receivers

Dual converaion DO have 2 crystals, the first is the one you plug in and is normally 10.7 MHz below channel frequency. The second is fixed and runs at 11.155 MHz which when mixed with the 1st IF of 10.7 MHz gives you the 2nd IF of 455 KHz.

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Old 11-26-2006, 07:03 PM
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Default RE: single vs. dual conversion receivers

right on mac man
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Old 11-27-2006, 10:40 AM
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Default RE: single vs. dual conversion receivers

Yes, dual conversion recievers do have two crystals as Mac Man says. Usually only one is removable or easily changed.
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Old 11-27-2006, 05:10 PM
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Default RE: single vs. dual conversion receivers

Yes dual conversion radio systems have two crystals. And I would go with the dual conversion if you plan to fly with other people alot. The only weakness of the single conversion doesnt seem to be range, but they are easily affected by other transmitters in the area. If you just plan to fly in your side yard however single conversion is fine. I just buy dual conversion for safety purposes and because I fly with other people at the same time alot. Good Luck!

Nathan
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Old 11-28-2006, 09:15 PM
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Default RE: single vs. dual conversion receivers

Mac_Man_UK certainly does know his stuff,and has the numbers to prove it(go ahead,do the math).Additionaly,I recall a page in Gearge Stiener's book ( Don't recall the title,and can't locate my copy raght now.Wife must have carefully stored it for me)expllaining how the frequency of the second crystal determines the frequency shift (JR/airtronics or Futaba/Hitec compatibility) of the receiver.
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Old 11-29-2006, 12:31 PM
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Default RE: single vs. dual conversion receivers

If I understand correctly, modern high-end single conversion receivers, like the FMA M5 and Berg 7P accomplish the function of the second IF through digital signal processing. That is, the analog IF signal is converted to a digital signal, then processed using the receiver's internal microprocessor to provide the filtering and image rejection functions that would have been accomlished in a analog second IF stage. In this way these receivers achieve the same flying performance capability as a "true" (hardware implemented, not software) dual conversion receiver.

Edited for clarity.
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Old 11-29-2006, 03:13 PM
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Default RE: single vs. dual conversion receivers

Firstly, the FMA M5 is a dual-conversion receiver (and a very good one).

Secondly, the Bergs (and a growing number of other SC receivers) do use a microcontroller-based decoder to help reduce the effects of interference from varous sources.

This alone can not significantly mitigate the effects of signals which appear on the image frequency to which SC receivers are sensitive.

While the Berg (and some other SC) receivers are perfectly adequate in many situations, the rather small price/size/weight difference that exists between SC and DC receivers means there's little reason not to opt for the latter if you're flying in anything other than a very remote area with very few others sharing your airspace.

99% of the time, a SC receiver will be just fine. However, if you're worried about that 1%, a few dollars spent on a DC receiver might be a good investment.
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Old 11-29-2006, 07:20 PM
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Default RE: single vs. dual conversion receivers

Thanks for the correction on the M5. I wasn't aware it was DC. I have several and they work very well.

I don't understand why the image on modern SC receivers isn't handled with dsp and an appropriate choice of the intermediate frequency. Maybe doing so is not economical? Manufacturing cost requirements for RC receivers are very restrictive I suppose.
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Old 11-29-2006, 11:57 PM
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Default RE: single vs. dual conversion receivers

DSP can only work with the information that comes from the receiver itself. If you're running SC and there's a whole heap of noise or other RF on the image frequency then the DSP can only do so much.

If the signal on the image frequency is strong enough (compared to the signal from your transmitter) there's just no way any DSP system can extract the information that's been lost.

Besides which, why bother with SC you can buy a really good 6-channel full-range DC receiver with DSP that weighs just over a quarter ounce for as little as $17.
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Old 11-30-2006, 10:55 AM
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Default RE: single vs. dual conversion receivers


ORIGINAL: JPMacG

Thanks for the correction on the M5. I wasn't aware it was DC. I have several and they work very well.

I don't understand why the image on modern SC receivers isn't handled with dsp and an appropriate choice of the intermediate frequency. Maybe doing so is not economical? Manufacturing cost requirements for RC receivers are very restrictive I suppose.
Yes economics has a hand in the choice of the If, but so does the selectivity requirements of the the receiver. Choice of the IF determines the selectivity of the receiver.
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Old 11-30-2006, 12:21 PM
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Default RE: single vs. dual conversion receivers

What Dirtybird says is correct. I would add the JR filters work but they are still no replacement for a good DC design. Just a shot at keeping the cost down .
Sometimes you need to look past the distributor's hype.
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Old 11-30-2006, 01:35 PM
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Default RE: single vs. dual conversion receivers

455 kc is chosen because that is standard that has been around for 75 years and the circuitry for it can be found in the radio engineers hand book. it is a design that has been used in millions of transister radios.
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