2 videos: The Wadley-Loop based Yaesu FRG-7 Communications Receiver

[w2aew]

A friend of mine asked me to do a little work on his Yaesu FRG-7 Communications Receiver.  In the process, I made two videos.  One that describes how the Wadley Loop "drift cancelling" architecture works, and one on how to use/tune the FRG-7.  It is interesting to look at "old technology", because you never know when it might be leveraged to fix a modern problem.  In fact, there as a paper published last year that talked about using the Wadley Loop as part of a coherent optical receiver...

Here's the first video on the basics of the Wadley Loop:



And here's the 2nd video on the operation of the FRG-7:



Enjoy!

[@rt]

It’s probably easy to find a problem to solve when you’re dealing with the best domestic solid state HF receiver for it’s price point that has ever,
and will ever be made  I never looked into what made this so, your vids should be interesting!

[C]

When looking at information for "Wadley-Loop" on the net, keep in mind that some of this information is wrong.

w2aew is good in what he stated, some facts on the drawing at 1:40 are incorrect or incomplete. I have seen radios with filters adjusted wrong do to the missing information.

When you look at drawing at 1:40 think of the following.
You have a radio with a 1 Mhz tunning range with a up converter in front of this.

This should make it easy to see that the second BPF has a simplified BW stated. While tuned to the top or bottom of 1 Mhz tunning range, this filter needs to pass the sidebands of the desired signal.
You need
Bottom - LSB to Top + USB
Not a big deal here, but for some radios this is very important fact.

This leads to first BPF also having a simplified BW stated.
This filter needs the bandwidth of above filter + drift of first oscillator. If this filter BW is too small you have the drift canceled and desired signal removed or reduced due to this filter. At edge of 1 Mhz tunning range, the desired signal is moving up and down of the edge of the filter's bandpass when first oscillator changes.

One thing often missed is real time correction. Tunning to 1 Hz or less is possible while the first oscillator is or has drifted a large amount. The error correction is exact.   

You often see stated that a "Wadley-Loop" receiver must be triple conversion, this is incorrect, double conversion will work and has been done and can result in a better radio.

[AF6LJ]

Some of the first Wrong information is The wadley conversion scheme is not a loop.
Where is the feedback, there is none.
Calling this a loop is a common mistake and actually separates those who know what is going on from those who do not.

There is no "Loop" in using an oscillator in the first conversion stage summing with the incoming frequency and in the second stage of conversion using the same oscillator in the difference mode.

[C]

Depends on how you look at it. To me a loop does not imply feedback.

"Wadley-Loop" is a dirft cancellation loop.

You have loop with half containing the error, and half containing the error correction.
Guess you might call the paths a box, like how it is drawn, but loop conveys more information.
What do you call a circle?

If you truly understand then calling it "wadley conversion scheme" is a fail because you can have input frequency = output frequency. Where this might be used I have no idea but it is possible.

[AF6LJ]

Depends on how you look at it. To me a loop does not imply feedback.

"Wadley-Loop" is a dirft cancellation loop.

Again there is no loop, If you say there is a loop you haven't even the slightest idea what is going on in that circuit.

You have loop with half containing the error, and half containing the error correction.
Guess you might call the paths a box, like how it is drawn, but loop conveys more information.
What do you call a circle?
You have no idea how the thing works and this is how misinformation gets spread.


If you truly understand then calling it "wadley conversion scheme" is a fail because you can have input frequency = output frequency. Where this might be used I have no idea but it is possible.

[C]

I stated why I and others call it a "LOOP"
All the many brands & models of radios I have worked with call it a "LOOP"

So you have your name, I and others call it the "Wadley-Loop"
Pick something else and show your understanding is better then mine.

[AF6LJ]

I stated why I and others call it a "LOOP"
All the many brands & models of radios I have worked with call it a "LOOP"

So you have your name, I and others call it the "Wadley-Loop"
Pick something else and show your understanding is better then mine.

Drake and Hygain didn't call it a loop.

If you want to perpetuate misinformation that is your business.
To anybody who knows how this works, and has worked on a few of them such as I, we know there is no loop in the Wadley conversion scheme.

It is another one of those "the Internet says so, therefore it must be true."...
I'm done.
Go learn how it works.

[Kalvin]

There is as much loop in the Wadley Loop as there is nut in a peanut.

[C]

Internet did not exist when I first started working on radios containing a Wadley-Loop. None were made by a Amateur Radio Mfr.
I did not work on a few, it was a lot, from many Mfrs and models
 
"Wadley-Loop" is a dirft cancellation loop.

If you want to perpetuate misinformation that is your business.

You are the one doing the misinformation.
You calling it a different name does not prove knowledge.

If you have knowledge, prove something I said in this thread is wrong.
 

[chris_leyson]

I would tend to agree with AF6LJ, there is no loop in a Wadley loop, from a control system point of view it's all feed forward. The term "drift cancelling loop" is misleading as the words cancelling and loop would imply some sort of feedback mechanism when there isn't any. That being said it is a nice frequency translating method.

[C]

I would tend to agree with AF6LJ, there is no loop in a Wadley loop, from a control system point of view it's all feed forward. The term "drift cancelling loop" is misleading as the words cancelling and loop would imply some sort of feedback mechanism when there isn't any. That being said it is a nice frequency translating method.

The whole point of a Wadley-Loop is the dirft cancellation of first oscillator.
For the first oscillator to second mixer there are two paths, frequency change in one path is countered by frequency change is other path. Mathematics X-X = 0
What Dr. Trevor Wadley stated in the 1940s

[AF6LJ]

I would tend to agree with AF6LJ, there is no loop in a Wadley loop, from a control system point of view it's all feed forward. The term "drift cancelling loop" is misleading as the words cancelling and loop would imply some sort of feedback mechanism when there isn't any. That being said it is a nice frequency translating method.

It is more appropriate to call it a drift canceling synthesizer. The second local oscillator signal is synthesized from difference between the comb generator (harmonic generator), and the variable first local oscillator. 

[chris_leyson]

Totally agree, the effects of the drift are cancelled by having the 2nd LO offset by a fixed amount from the 1st LO but the drift in the 1st LO is never corrected for. Still think it's a nice frequency conversion method and the only drawback I can see are issues with spectral purity in the 1st LO.

[C]

Limiting thinking to sub case of use.
Common sense if you want a bunch of frequencies you build a version for many  frequencies.

Totally agree, the effects of the drift are cancelled by having the 2nd LO offset by a fixed amount from the 1st LO but the drift in the 1st LO is never corrected for. Still think it's a nice frequency conversion method and the only drawback I can see are issues with spectral purity in the 1st LO.

The 2nd LO offset does not have to be by a fixed amount.
 

[AF6LJ]

Totally agree, the effects of the drift are cancelled by having the 2nd LO offset by a fixed amount from the 1st LO but the drift in the 1st LO is never corrected for. Still think it's a nice frequency conversion method and the only drawback I can see are issues with spectral purity in the 1st LO.

The common problem with this method of frequency conversion is feed through from the harmonic generator. usually at the start and end of the tuneable sub band.
The first LO running above the incoming frequency is free running and spectral purity usually is not a problem and can be dealt with easily enough.

The harmonic generator tends to be dirty...
With that said the second LO (first LO + harmonic) can have spectral purity issues.