The TRF-One am radio

[Oldmadham]

Originally Posted by paulsherwin

The vast distances in Australia would have made LW fairly pointless. LW coverage is just right for Europe, with a single transmitter covering a single typical sized country, but there wouldn't be much benefit in covering a quarter of NSW or QLD. The Aussies just used SW to cover the rural areas, and followed a North American city based model with relatively low powered MW transmitters for their urban coverage

Not quite, 6WF in Perth, Western Australia was 55kW, as was 6WA Wagin, 6DL Dalwallinu was 10kW---all MW stations.
Most of the other ABC MW stations were 5kW.

The Commercial stations were 2kW, which sounds like a handicap, but they were further up the band & could build more efficient antennas.

There were MW ABC & Commercial transmitters at many country towns, giving good coverage of the south of WA.

VLW & VLX were the shortwave broadcasters in WA, covering most of the North of that State.

They also served as backup programme sources for 6DB Derby, which was many weary miles of of open wire pole route away from Perth, in the far north of the state, & often lost that normal feed.

Back in 1967/68, I was in Wyndham, even further north.
At night, we could listen to 8DR Darwin, 446km away, as the radio signal flies, (& of course, to VLW/VLX, if we had a SW Rx).

From memory, the only other domestic SW outlets were serving Queensland's north.

Originally most of the Capital city stations started up on LW, but soon changed to MW.

[Oldmadham]

By the way, I hate to be "that guy" (actually, I love it!), but a TRF radio normally meant a radio with one or more stages of tuned RF amplification, not an aerial coil, followed by one or more untuned amplifiers.
A nice radio ---but it's not a TRF!

[Herald1360]

Err..... doesn't it have exactly that- one tuned RF amplifier stage?

That it's followed by more untuned stages doesn't change that.

What it doesn't have, unlike more traditional TRFs is a tuned detector stage.

Perhaps it should simply be called a Straight Set.

[Andrew2]

I'd call it a TRF, as it's not a superhet and the only tuned cct it has is at signal frequency.

[Dave757]

Hi,

So would I.

The only possible query could be that being a ferrite rod, the antenna winding is tuned
and then inductively coupled to the RF amp but to me this is a minor academic point.

It does not detract from the circuit being the only tuned input to the RF amp, and to
me this makes it very definitely a TRF.

Kind regards
Dave

[Argus25]

Originally Posted by Oldmadham

By the way, I hate to be "that guy" (actually, I love it!), but a TRF radio normally meant a radio with one or more stages of tuned RF amplification, not an aerial coil, followed by one or more untuned amplifiers.
A nice radio ---but it's not a TRF!

It does have the one (and only one) tuned radio frequency stage, which is why I called it the TRF-ONE.

Part of it was to try to make a radio with good performance with just the one tuned stage and the single gang V/C which reminded me of radios I built as a boy, which were mainly either crystal sets or regeneratives.

And that magical feeling or effect watching as the closely spaced V/C plates mesh in and out as the stations passed by. So The V/C was placed in a prominent position and the radio made "Open Frame" to see the V/C easily as you turn the tuning knob. Rather than boxing it all in.

However the height of the ferrite rod supports match the front panel, so if you flip the radio over, to change the batteries, it stays stable on the bench.The front panel handles make it easy to grab and provide some protection for the panel controls & dial.

It is pretty obvious though, from the way I built it, attaching the V/C to the pcb, the pcb assembly could be swapped out for anything, including an AM/SW superhet, FM radio, regenerative, multi-stage TRF etc. I had this back up plan in mind, in case the whole notion of the design with the LM372 fell on its head, so all the other work would not be wasted. But it has worked out so well, it is staying as it is.

[Argus25]

Originally Posted by G6Tanuki

Probably the closesat I ever did to your TRF was using a 2N3819 buffer feeding a pair of uA703 RF amplifiers, and a full-wave diode detector.

I have a collection of the UA703 and was also giving some thought to using these in a radio one day, they are also very beautiful and interesting ICS.

Also, I investigated what other OP amps of the period I could try as plug in replacements for the LM741. Yesterday some 1973 vintage LM307's arrived in the post. Substituting one of these for the LM741 I could not detect any difference in the performance, but I have not tried it with the signal gen and scope yet to check the power output prior to clipping. I also have some mil spec LM107's on order.

I would be interested in opinions on LM741 vs LM307 any thoughts ?

[Oldmadham]

Considering this purports to be a "Vintage Radio" site, I would have thought the definition which was standard when TRFs were common should be used.

A Crystal set has one tuned circuit at RF, so does a Regen set & the front end of a Superhet (indeed, some Superhets have a tuned RF amplifier stage before the mixer.), but I have never heard them referred to as TRFs.

Similar devices to that described were made in the early valve days, but were not popular enough to attract a common name.
"Amplified crystal set" does not apply, as in the device of that name, all the gain is at audio frequency.

https://www.radioexperimenter.us/rad...-receiver.html

Some of the disadvantages referred to in the link above are indeed, alleviated by untuned gain prior to the detector, but the selectivity is still limited by the single tuned circuit.

https://www.radioexperimenter.us/rad...-receiver.html


https://www.radioexperimenter.us/rad...eivers/lc.html

https://www.radioexperimenter.us/rad...-receiver.html

[Argus25]

Originally Posted by Oldmadham

Considering this purports to be a "Vintage Radio" site, I would have thought the definition which was standard when TRFs were common should be used.

A Crystal set has one tuned circuit at RF, so does a Regen set & the front end of a Superhet (indeed, some Superhets have a tuned RF amplifier stage before the mixer.), but I have never heard them referred to as TRFs.

Yes it is interesting.

If you look on Google at "TRF radio circuits" or circuits labelled as that, you will find that most radios called "TRF" in popular culture, in the bare minimal form, have a tuned radio frequency resonant circuit (be it a ferrite rod or antenna coil and wire antenna), then at least one stage of radio frequency amplification, then a detector and then typically the audio amplifier. Presumably this is where the Tuned Radio Frequency naming came from. Maybe it should have been ATRF as in amplified tuned radio frequency.

I don't think it makes a difference to the naming if you have more than one tuned circuit and more than one active radio frequency amplifier stage which improves the selectivity over a single tuned stage, and that can be expanded to as many stages as you want.

If the detector is placed directly on the input tuned circuit, it is then by definition, a crystal set.

One thing is due to the high Q of the ferrite rod coil in this radio and air variable capacitor and the minimal loading on it, the selectivity in practice appears surprisingly good.

The AGC in this IC is amazing with near and far stations coming it at a similar volume. Also as I mentioned, it is very odd rotating the radio off axis to the carrier, normally in most of my ferrite rod based superhet radios, the volume level drops as its rotated, despite the radio's AGC. With this LM372 AGC arrangement the level stays uniform until rotated about 85 to 87 degrees off axis and the signal suddenly drops out. This sort of effect might be handy for direction finding.

I have attached a circuit of a "TRF radio" lifted from the net with a single tuned stage. The RF amplifier output is broadly tuned, not tuned by another variable capacitor gang. If this also could not be called a TRF radio on a technicality, one wonders what you could call it.

[Oldmadham]

Originally Posted by Argus25

If you look on Google at "TRF radio circuits" or circuits labelled as that, you will find that most radios called "TRF" in popular culture, in the bare minimal form, have a tuned radio frequency resonant circuit (be it a ferrite rod or antenna coil and wire antenna), then at least one stage of radio frequency amplification, then a detector and then typically the audio amplifier. Presumably this is where the Tuned Radio Frequency naming came from. Maybe it should have been ATRF as in amplified tuned radio frequency.

I don't think it makes a difference to the naming if you have more than one tuned circuit and more than one active radio frequency amplifier stage which improves the selectivity over a single tuned stage, and that can be expanded to as many stages as you want.

If the detector is placed directly on the input tuned circuit, it is then by definition, a crystal set.

One thing is due to the high Q of the ferrite rod coil in this radio and air variable capacitor and the minimal loading on it, the selectivity in practice appears surprisingly good.

The AGC in this IC is amazing with near and far stations coming it at a similar volume. Also as I mentioned, it is very odd rotating the radio off axis to the carrier, normally in most of my ferrite rod based superhet radios, the volume level drops as its rotated, despite the radio's AGC. With this LM372 AGC arrangement the level stays uniform until rotated about 85 to 87 degrees off axis and the signal suddenly drops out. This sort of effect might be handy for direction finding.

I have attached a circuit of a "TRF radio" lifted from the net with a single tuned stage. The RF amplifier output is broadly tuned, not tuned by another variable capacitor gang. If this also could not be called a TRF radio on a technicality, one wonders what you could call it.

So many of these circuits are scattered over the Internet by, in the main, people who "saw it somewhere else"
& decided to post it.
It only takes one person to misname something, for it to spread like wildfire, becoming the new convention.

I was looking at a "Ham Wiki", one day, & was confronted by a bridge rectifier, which they called a "Kratz" rectifier.
I had never heard that term before, & Googling found no other references to the elusive "Kratz", so I amended the wiki to read "bridge rectifier".

Latterly, I have determined that Mr Graetz was responsible for the original design, & sometimes, very rarely, I have heard it referred to by his name.

Graetz is not "Kratz", however.
I wonder how many thousands of people are now spreading the Gospel of the almighty "Kratz" across the Internet!

[Argus25]

Originally Posted by Oldmadham

It only takes one person to misname something, for it to spread like wildfire, becoming the new convention.

Well I agree on this. That is why I said "TRF in popular culture.."

I was complaining about exactly this recently on another thread, where the voltage generated by a collapsing magnetic field in an inductor, disconnected from a source of external power, was incorrectly called "back emf" where that term (derived from counter emf) strictly speaking should only be applied when the coil is powered by an external source and the emf generated by the inductor opposes the applied voltage. But its usage is all over the net and everybody appears to understand what it means.

It reminds me to some extent of the problem with American word spelling, but the argument was won by the notion that the modified word/s still conveyed an unambiguous meaning and were improved in efficiency with fewer letters.

So what would you propose an AM radio with a single tuned radio frequency stage and an RF amplifier prior to the detector should be called ? If it has a catchy ring to it, I'll consider renaming the radio.

PS: I guess wikipedia got it wrong too ?

"A tuned radio frequency receiver (or TRF receiver) is a type of radio receiver that is composed of one or more tuned radio frequency (RF) amplifier stages followed by a detector (demodulator) circuit to extract the audio signal"

[Argus25]

Looking more at the Wiki page on Modern Usage, the ZN414 single IC radio is defined as a TRF.

[G6Tanuki]

I'd say that "TRF" is any receiver in which there is signal-frequency-amplification but no frequency-conversion before detection, and signal-frequency selectivity exists.

A "direct conversion" receiver with a RF-amp is therefore a TRF - though one without a RF amp would not deserve the name, neither would a crystal-set.

(another term which confused me a lot when first getting into old radio stuff was to describe a mixer stage in a superhet as the "first detector").

[julie_m]

Or you could think of a direct-conversion receiver as being a superhet, but with an "IF" of DC .....

[G6Tanuki]

Originally Posted by julie_m

Or you could think of a direct-conversion receiver as being a superhet, but with an "IF" of DC .....

Yes, that's how I once explained it to someone who refused to understand how it could possibly work!

[Oldmadham]

Originally Posted by Argus25

Looking more at the Wiki page on Modern Usage, the ZN414 single IC radio is defined as a TRF.

Wiki, by its nature is not a definitive source--refer my "Kratz" rectifier" comment.

I don't know what to call a radio with only one tuned circuit, maybe "a simple receiver".
How about one with no tuned circuits, like an SDR?

[Argus25]

Originally Posted by Oldmadham

Wiki, by its nature is not a definitive source--refer my "Kratz" rectifier" comment.

I don't know what to call a radio with only one tuned circuit, maybe "a simple receiver".
How about one with no tuned circuits, like an SDR?

Due to the poor noise rejection of SDR's Silicon Chip just published an article with a tuned circuit for their front end with a resonant circuit tuned by the usual transistor radio V/C, seems hard to escape them.

[Argus25]

I just performed an interesting test on the TRF-ONE.

A while back some may remember a post on a piece of test equipment I designed called the H Field Transanalyser:

http://worldphaco.com/uploads/The__H...nsanalyser.pdf


The idea was to be able to create standard tables of performance on various transistor radios. One good bit of news is that Silicon Chip is going to re-create this as a kitset to help those restoring and aligning vintage transistor radios.

I got up to the point of documenting three vintage radios, The Hacker Sovereign, the Sony TR-72 and the Nordmende Clipper.

So I have added the TRF-ONE data to the table (attached).

It is quite different. The rms output voltage stays nearly perfectly stable the whole time, all that happens as the modulated RF signal is attenuated is that the audible modulation simply gets replaced by noise of a similar amount, at least in the spectrum around 1kHz that the rms meter is sensitive to. Its due to the super effective AGC in the LM372.

The relative signal to noise of the TRF-ONE on the subjective scale though is practically identical to the Hacker Sovereign ! and better than the Sony TR-72 and the Nordmende clipper which is a surprise.

The "clip Ratio" has less meaning for the TRF-ONE because its ends up as a constant at all RF signal levels (30% modulation), as there is always near 200mV rms out of the detector (detected modulation and/or noise) and it takes 250mV rms to drive the audio output stage to clipping. So I could have had a little more gain in the audio stages.

[johnyjf]

A beautiful job of work, you should be very proud of it!