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 Post subject: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 12:16 am 
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Joined: Nov Sun 26, 2017 8:22 am
Posts: 5
Walfords sells a radio he calls a REGEN TRF.
Can anyone here recommend any technical explanations how to build regen TRF radios? Transistors or tubes.
Walfords does not publish his schematic for all to see and discuss so the only way you see that schematic is in his purchased kit.
Which I did buy.
But can't really discuss without sharing his protected schematic.
So I was wondering if there was another regen TRF to discuss that is in public view.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 2:39 am 
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Joined: Aug Thu 06, 2015 2:20 am
Posts: 106
KB3BYT wrote:
So I was wondering if there was another regen TRF to discuss that is in public view.

Here's one that I use all the time as a test bed for my regen projects.

I t has a high quality PC board with all the components mounted on the front panel which makes it very easy to implement new designs.

The schematic is below.

What would you like to discuss?


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 4:00 am 
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I found a clearer schematic on 4sqrp web page....: ozarkpatrol_schematic.jpg

I was hoping to find an answer to the question of WHAT IS A REGEN TRF

I thought a TRF was a TUNED RADIO FREQUENCY circuit and
a regenerative receiver was a different animal and thats why we call it a REGEN.

So where it gets weird is Walford calls his radio a "REGEN TRF".

The OZARKPATROL description says:
The Ozark Patrol circuit is a two-band shortwave receiver, using only three NPN transistors in its circuit. It employs a reflexed regenerative detector to maximize gain from its simple design, followed by a two-transistor audio amp. It is capable of operating from a simple wire antenna.

Its not that I am looking for another regenerative receiver to build.
I have built a few and made them available .... and gave away a bunch of them.
http://www.learnmorsecode.com/regen/00regen.html
I've heard France and Cuba on $6 home brewed radios.

The WALFORD ROCKWELL REGEN TRF is quite an oddball circuit compared to
the rest I have found on the internet.
It uses four BS170 MOSFETs which I just learned was nearly the same as 2N7000 MOSFETS
.....which I am more accustomed to using as on / off switching... not RF and audio amplification.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 4:07 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 25688
Location: SoCal, 91387
Here's my 3 tube Regen; works terrific.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 4:13 am 
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When I first read the title of your thread I went "Huh?? Regen TRF???"

You are quite correct. There are regen receivers and there are TRF receivers, although perhaps he is using TRF to distinguish it from a superhet.

As I mentioned, I use the Ozark receiver as a test bed to build different front ends.

All of my receivers use ferrite rod antenna coils with no external antenna or ground and their performance is comparable to my best handheld portable commercial receivers using their built in whips.

In the evenings I listen to SSB on the 80 and 40 meter bands picking up amateur nets along the East coast of the U.S. all with no external antenna.

I would like to suggest that you try a ferrite rod antenna coil in one of your builds.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 8:19 am 
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I bought ferrite rods but have not used them yet.
Can you point to any particular web page that shows radio building with a ferrite rod.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 10:59 am 
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Joined: Aug Thu 06, 2015 2:20 am
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Here are some schematics of regen receivers which I have built using the Ozark receiver chassis as a test bed.

All use ferrite rod antennas the high Q of which is a necessity in some of the circuits which use the intrinsic Base-Emitter capacitance as one of the Colpitts feedback elements, about 10 turns to tune up to 10 MHz.

For an audio amplifier I frequently use a TL431 shunt regulator as shown in schematic 5.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 6:03 pm 
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How do I get a BIGGER clearer picture of these 7 circuits?

I've played with 716 resonators:
http://www.learnmorsecode.com/716/index.html
http://www.learnmorsecode.com/716/716.html

then tl431 for amplification:
http://www.learnmorsecode.com/amp/tl431.html
and heard 40 meter CW France :
http://www.learnmorsecode.com/amp/f5inqso.mp3

but never used ferrite antennas.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Mon 27, 2017 6:33 pm 
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Joined: Aug Thu 06, 2015 2:20 am
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KB3BYT wrote:
How do I get a BIGGER clearer picture of these 7 circuits?


Here is a start.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Tue 28, 2017 1:55 am 
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There is the possibility that the Walford circuit you mentioned is a regen with a tuned RF before it, which would indeed make it a regen TRF.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Tue 28, 2017 2:09 am 
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Joined: Aug Thu 06, 2015 2:20 am
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Wouldn't a tuned front end in a regen receiver be somewhat redundant?

It would likely offer little in the way of improved selectivity.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Tue 28, 2017 2:32 am 
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Joined: Mar Tue 11, 2014 2:54 am
Posts: 51
LM386 wrote:
Wouldn't a tuned front end in a regen receiver be somewhat redundant?

It would likely offer little in the way of improved selectivity.


Several reasons a tuned front end in a regen can improve performance.

First of all, a regens sensitivity to signals falls off greatly when it is taken out of oscillation. This is really pronounced when detecting AM signals. The receiver will be most sensitive when just starting to oscillate. Old time hams were aware that a regen was hard to beat for code, but for AM they are more deaf ( weak signal work). A tuned front end ahead of a regen will be comparable to a good superhet in detecting AM signals. An untuned front end has the same effect, but suffers from some of its own problems.

A tuned front end works better at eliminating station "break through". This is where a strong station close in frequency occupies 100khz or so on the dial and is untunable.

Untuned front ends can suffer from several problems. First is it can actually act as a detector itself, passing this audio through to the next stage. Second it can be easily overloaded by nearby stations and cause IMD. Third, when biased properly to prevent "detection" current draw goes up.

Perusing old SW Craft magazines you will find many designs with tuned front ends ahead of a regen detector. Also I think there were military versions that used the same configuration.
If I believe properly, the National SW3 has a tuned front end ahead of its regen detector.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Tue 28, 2017 2:37 am 
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Here is the SW3 manual.

http://bama.edebris.com/manuals/national/sw3/

It indeed does have a tuned RF stage ahead of the detector.


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Tue 28, 2017 2:49 am 
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Joined: Mar Tue 11, 2014 2:54 am
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Here is a good video of another National regen with tuned RF.

https://www.youtube.com/watch?v=PrueVuZJz-M

You can see it does well on the AM ham stations, I would say if it were just a straight regen, those AM signals would be down in the "mud". They had two modes back then. CW and " AM Phone". The tuned RF stage helped out tremendously on "phone".


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Wed 29, 2017 2:39 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 612
Location: Tokyo
James Millen's notes on designing regens with RF stages can be found here:

http://www.antiqueradios.org/gazette/SWevol.htm

In particular, scroll down to An Analysis of AC Operated Shortwave Receiver Design

RF stages must be properly shielded and screened, otherwise signals will find their way around the RF amp and into the detector. Details can be found in radio HBs from the 1930s, both the ARRL and E&E. Finding the sort of ganged VCs that Millen used is very difficult today. While the RF amp can be tuned separately from the detector, RF tuning will affect regeneration level and vice versa. It does take a bit of fiddling to tune in a station. I actually don't mind that, but it certainly isn't a superhet kind of tuning experience. Rather than use an RF stage, I've come to prefer simply zero-beating the detector with an AM station. Of course, the tuning has to be precise enough, the detector stabile enough to do this.

I think the 'secret' to using a regen well is the RF attenuator between the antenna and the detector or RF stage. Keep the incoming RF level as low as possible without losing the signal in the noise. Strong signals force you to back down on regeneration and that worsens selectivity and sensitivity. Make up the gain in the audio section.

An observation on regen AM sensitivity: about the same as a pentagrid converter (eg, 12BE6), so adequate up to at least 7 or 8MHz. At my present noisy location, a pentagrid front end is good to almost 12MHz!

Rob


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Wed 29, 2017 5:14 am 
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shinkuukan wrote:
Strong signals force you to back down on regeneration and that worsens selectivity and sensitivity.

Well yeah, but upon passing a strong station, I'll turn up the regen control for the weaker ones, until I run into another strong station, then down it goes until I pass it, and up again.

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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Nov Thu 30, 2017 8:54 am 
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Joined: Dec Sun 14, 2008 3:33 pm
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Location: Tokyo
I didn't make my point very clearly. I'll try again. But first, I emphasize that this is just my preferred way of using a regen. A description, not a prescription.

Regen selectivity is all on the nose, the bandpass skirts are wide. Triangle shape rather than the box shape of a good filter. You get the best results when the incoming RF level is adjusted (ie, attenuated) to keep signals as close as possible to that nose, and away from the skirts.

The first step is to adjust the RF attenuator so that touching the antenna lead to the receiver just slightly increases noise level. You leave it there (for a given band and time); occasionally really strong signals will force you reduce RF level even more. This is standard practice for communication receivers: set the RF gain or the attenuator so that incoming noise off the antenna slightly exceeds the receiver's own generated noise level.

Of course doing this reduces the audio volume level, but the signal to noise ratio will be as good as it can get. You make up for the lower volume with more audio amplification, rather than reducing RF attenuation.

Rob


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Dec Thu 07, 2017 4:44 am 
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Joined: Nov Sun 26, 2017 8:22 am
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I bought it.
I built it.
I heard the world.
EVERYBODY should build a handful of these and just hand them out to kids....
or build them with the kids.
This WALFORDS ROCKWELL REGEN-TRF should be every kids first radio... just like we thought
of crystal radios in our youth.
I'm impressed.
schematic is here:
http://www.learnmorsecode.com/regen/WALFORDS/index.html


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 Post subject: Re: WALFORDS REGEN TRF
PostPosted: Dec Thu 07, 2017 7:37 am 
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Joined: Aug Thu 06, 2015 2:20 am
Posts: 106
Although this receiver appears to use a 2 gang capacitor, both gangs are in parallel for the lower band and only one gang is used for the upper band.

The RF amplifier is untuned and followed by a tuned Colpitts oscillator.

Does this mean that it is truly a TRF Regen receiver????

The use of Mosfets interests me. They have a very large input capacitance (60pF) which will likely limit them to use in the lower shortwave bands but instead of being a disadvantage this intrinsic Gate-Source capacitance can likely be used as the feedback capacitors in a Colpitts oscillator circuit such as the modified circuit shown below with TR3 acting as the detector.

Because I like simple and because my experience has been that with a ferrite rod antenna no RF stage or external antenna are necessary for most shortwave listening, my intention is to try the simplified second circuit below.

I don't know with the values shown whether the biasing will be correct for the detector FET if the oscillator and detector FETs are direct coupled, but if not, the detector FET can be capacitively coupled and biased as shown in the modified first schematic.


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