Wikipedia's Wadley Loop  errors and miss statements - Page 1
Forum section: electronics / general

author: C
author_rank: Super Contributor
timestamp: September 23, 2015, 12:24:38 am
content: Does anyone here that is good at teck writting what to correct this page?Guess the first question should be if anyone here can see the errors?As a hint,What is a superheterodyne radio receiver problem vs a change needed for a Wadley_Loop to function?https://en.wikipedia.org/wiki/Wadley_LoopC

author: C
author_rank: Super Contributor
timestamp: December 28, 2015, 05:24:29 am
content: HiStarted this a long time ago. Some better wording might help.First what is a "Wadley Loop"?It is a way to cancel oscillator drift.You use a lower frequency stable oscillator or signal to generate harmonics that are used to correct results of a High frequency oscillator drift.Look at the difference between harmonics and the oscillator.If difference increases for harmonics below oscillator freq ,then the harmonics above oscillator freq are decreasing.One set of harmonics will correct the change while the other set makes it a 2X drift.This is the foundation of Wadley Loop correction.It is linear change.This idea can be used many places, one is aDouble Conversion Superheterodyne Radio Receiver to cancel first oscillator drift.Double Conversion Superheterodyne Radio ReceiverHere the First oscillator is one with the drift.The correction needs to happen at second mixer oscillator input so that while the output of first mixer changes, the output of second mixer does not change.Harmonics get weaker for higher harmonics, so might need a receiver just for harmonics.To convert the Double Conversion Superheterodyne Radio Receiver to aDouble Conversion Superheterodyne Radio Receiver with "Wadley Loop" correction the following steps are needed.Take a copy of the above block diagram and flip it top to bottom.1. The first oscillator is now driving two mixers.2 Where the second oscillator would be doing the same as first, A block swap is needed. Swap the position of the second oscillator and the lower second if amplifier.3. Lower antenna rf input is the harmonic input.If some of you are looking for this block diagram on web, you may not find it.Was common in old military receivers I worked with.This is a double conversion wadley loop receiver!The results of a first oscillator drift is canceled at the second mixer that is processing RF input just like other designs..This shows one error where their is a statement that the Wadley Loop requires triple conversion.First let's look at some Band Withs for the Filters in the RF path.1. You have the RF signal that you want to receive. Call this "Signal Bandwidth"2. You have the difference between harmonics. Call this "Harmonic step size"For these types of radios you normally change the first oscillator freq by "Harmonic step size".That second oscillator in lower right then changes over a range of "Harmonic step size".Note if you are changing the first oscillator that for a signal like AM you will have 1/2 the signal extending above or below when at end of the second oscillator's range.Now have enough information to compute some bandwidths.Double Conversion Wadley Loop Receiver1. RF path{ The RF amplifier is a min of "Signal Bandwidth" + "Harmonic step size".2. RF path: The first IF amplifier is a min of "Signal Bandwidth" + "Harmonic step size" + ( +-oscillator drift). Option of tunable IF with min of "Signal Bandwidth" + ( +-oscillator drift)3. RF path{ The second IF amplifier is "Signal Bandwidth"4. Harmonic path: The first IF amplifier is a min of ( +-oscillator drift)5. Harmonic path: The second IF amplifier is a min of "Harmonic step size" + ( +-oscillator drift)6. Harmonic path: The first RF amplifier needs to prevent the image Harmonic to mixer.The detail on bandwidth's they are often stated wrong.Now if you look at the block diagram again, You could think of the First IF amplifier in RF path as the RF input of a Single conversion Superheterodyne Radio Receiver. This lets this first IF amplifier to be changed to a tunable IF amplifier with a min of "Signal Bandwidth" + ( +-oscillator drift). The option above. This would be tunned with second oscillator change.So to be complete what bandwidths are needed for triple conversing where you tune the oscillator to third mixer in RF path? Triple Conversion Wadley Loop Receiver1. RF path: The RF amplifier is a min of "Signal Bandwidth" + "Harmonic step size".2. RF path: The first IF amplifier is a min of "Signal Bandwidth" + "Harmonic step size" + ( +-oscillator drift)3. RF path: The second IF amplifier is"Signal Bandwidth""Signal Bandwidth" + "Harmonic step size".4. Harmonic path: The first IF amplifier path is a min of ( +-oscillator drift)5. Harmonic path: The second IF amplifier is a min of "Harmonic step size" + ( +-oscillator drift)6. Harmonic path: The first RF amplifier needs to prevent the image Harmonic to mixer.7. RF path: The third IF amplifier is a min of "Signal Bandwidth"#2 could be a tunable IF with a min of "Signal Bandwidth" + ( +-oscillator drift)#3 could be a tunable IF with a min of "Signal Bandwidth"Both tuned by oscillator that does linear change between steps.First oscillator correction:Look at block drawing of Double Conversion Superheterodyne Radio Receiver with "Wadley Loop" correction.1. Put a up arrow showing direction of first oscillator drifting up.2. Put a arrow showing direction of first mixer output due to #1.3. Put a arrow showing direction of second mixer oscillator input due to #1 to correct.4. Work around loop with arrows.Keep in mind that a mixer has two modes ADD or Difference and the Oscillator input could be above or below the other input.So some may be thinking why bother correcting Wikipedia, This is old stuff you use phase locked loops these days.Phase locked loops do drift and take time to correct, this is fast.Above a receiver was used as an example. This idea can be used for transmitters and other electronics.Most radio examples show use of 1Mhz Harmonic step. I worked with some radios that were 100Khz Harmonic step, in 4 RF bands. And larger Harmonic steps also work.If you really understand the Double Conversion Wadley Loop path, you see that it could be a triple conversion with two oscillators being drift corrected.You could have more oscillators effecting the first mixer and the cancel signals effecting the second mixer.So the QUESTION, is someone here willing to help correct Wikipedia and make it easy to understand?My tech writing and drawing is not that great.Think above has no errors, but could have missed something. Will edit if needed.C