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Nov 09, 2001, 10:49 AM
Certified Slopehead
tenover's Avatar

Single/Dual Conversion

What is Single vs. Dual conversion? I just bought a HiTec Focus 3 FM Transmitter, a feather reciever (which is single cinversion) and a 555 reciever which is dual conversion. They both work with thr transmitter, but what's the difference
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Nov 09, 2001, 10:52 AM
Electrics rule
risto's Avatar

Nov 09, 2001, 11:14 AM
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tenover's Avatar
Thanks for the link, I've read that before, but it's like trying to learn a new language. Basically, I don't have anything to worry about, right? The dual conversion just will allow a longer range
Nov 09, 2001, 12:01 PM
Registered User
Dual conversion is better at rejecting some common types of interference, that's all.

Some small single conversion receivers have poor range but it's not because they are single conversion it's because they are small and cheap.

Nov 09, 2001, 12:40 PM
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tenover's Avatar
Thanks, That's all I wanted to know...So it doesn't matter to your Tx whether your Rx is single or dual?
Nov 09, 2001, 01:36 PM
aka: A.Roger Wilfong
gnofliwr's Avatar
All other things being equal, the range is the same for single conversion vs. dual conversion. Dual conversion is better at ignoring some types of interference.

Unfortunalely, all things are not always equal. Single conversion receivers have fewer stages (RF, oscillator, mixer, IF, detector and decoder) than a dual conversion (RF, two oscillators, two mixers, two IFs, detector and decoder). This makes them lighter and less expensive. Each stage performs a specific task - to amplify, filter or frequency shift the signal. The RF stage's primary affects the receivers ability to handle weak signals, but if you're dealing with small models that will only ever be within a couple hundred feet of the transmitter, the rf stage is unnecessary - why have a receiver that will pick up a signal a mile away if your only 100' away? So, if you don't need the range, receivers can be made even lighter and less expensive by eliminating the RF stage. For ecconomic as much as technical reasons, it doesn't make sense for a manufacturer to eliminate the RF stage from a dual conversion receiver so this usually only happens in single conversion receivers

So if you're looking for a rule of thumb...

If you buy a dual conversion receiver is is most likely a full range unit. If you buy a single conversion, you need to check.
Nov 09, 2001, 03:40 PM
Registered User

single or dual?

agree with most of the stuff said above - however, a well-designed single conversion receiver with a good quality IF filter, and a good linear front end, has only one small disadvantage over a dual conversion receiver, but it has many advantages.

the disadvantage is that channels 11, 12, 13 and 14 MAY have an image which MAY make them sensitive to transmissions on channels 56 through 60 -- for this reason, JR does not supply receivers on channels 11 thru 14.

however, AMA recommends that single conversion receivers use a crystal below the channel frequency - image problem gone - but is it? in the case of fm receivers, this crystal below the carrier frequency, inverts the detected pulse and you will find that you need a change in the receiver to cope with that - another reason that JR does not supply receivers on channels 11 thru 14.

other than that, a GOOD quality single conversion can offer the same range, narrow-band selectivity and 3IM performance as a dual-conversion receiver, and that at lower parts count, cost and size, and at comparable, or slightly lower, price.

Nov 09, 2001, 04:20 PM
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Rotten Robbie's Avatar
The last two answers are very good. The image problem is the real problem.

Use the single conversion recivers like th Feather and GWS Pico for park flyers.

For larger airplanes and especilly gliders, use a good double conversion reciever.

FMA makes very good double conversion recievers at a very good price.

Nov 10, 2001, 12:20 AM
Registered User

Single/Dual Conversion

The main problem with single conversion Rx's is that they MAY also "recognize" a signal that is 23 channels up or down (the image frequency) from their intended channel. For example, a plane flying on ch 20 might be hit by a plane flying on ch 43. This is common to AM, FM and older PCM gear and has been called the 23-skidoo. This is a function of spacing of Tx's on the flight line and the relative flight path of the aircraft to the Tx's. Range is primarily a function of sensitivity.
Nov 10, 2001, 02:05 AM
Electrics rule
risto's Avatar
As I read AM modulation is not affected by this.

Current production techniques produce acceptably tight tuning and AM receivers (which are limited to signal ON/OFF, remember) typically limit their IF span to less than 5 Khz each way i.e., anything out of about 450 460 Khz is lopped off drastically thereby eliminating the 435 and 475 interference. So AM is happy as a clam with 20 Khz channel separation. The problem is with FM.

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