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 Post subject: TRF HOMEBREW RADIO
PostPosted: Jan Thu 16, 2020 2:36 pm 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 575
I'm not sure if this radio would be of interest. When I made it I got quite a surprise.

It had been a long time since I made an AM radio with a single tuned stage. I guess I got nostalgic about the single gang variable capacitor, starting off with Xtal sets etc.

I tried out a somewhat rare and interesting IC, The LM372. It was designed basically for an AM IF stage, but the curio with it is; it has an astonishingly wide range AGC.

So what happens with this radio (unlike any other AM radio I own) the level that appears out of the detector is always roughly about 200mV rms, regardless of the signal strength.

So as the signal weakens, it is merely replaced by about the same amount of noise. So it is a really odd effect, tuning it across the MW radio band, the weak and the strong stations all come out at the same level or volume.

I have attached a picture of this radio, I called it the TRF-ONE. Also I made an article about it:

http://worldphaco.com/uploads/THE_TRF-ONE.pdf


Attachments:
TRFONE1.jpg
TRFONE1.jpg [ 727.12 KiB | Viewed 1114 times ]
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 Post subject: Re: TRF HOMEBREW RADIO
PostPosted: Jan Thu 16, 2020 5:23 pm 
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Joined: Jun Sun 22, 2008 2:03 am
Posts: 908
Location: Burke, VA 22015
Interesting and old IC. Beautifully built radio! Thank you for posting it here.

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Binh


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 Post subject: Re: TRF HOMEBREW RADIO
PostPosted: Jan Thu 16, 2020 5:32 pm 
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Joined: Dec Sun 21, 2014 6:37 am
Posts: 2176
Location: Portland, TN, USA
Very nicely-done build, even if only the pilot lite glows! :D

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73, de Chuck K4CCW

If talk is cheap, it's because the supply usually exceeds the demand.


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 Post subject: Re: TRF HOMEBREW RADIO
PostPosted: Jan Fri 17, 2020 4:28 am 
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Joined: Feb Sat 08, 2014 7:43 pm
Posts: 76
Location: Denver, CO
Acorn, that is a sweet build!


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 Post subject: Re: TRF HOMEBREW RADIO
PostPosted: Jan Fri 17, 2020 7:59 am 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 575
bb.odin wrote:
Interesting and old IC. Beautifully built radio! Thank you for posting it here.


Thank you for that remark.

I like the Dr. Mu image you have used.

I wrote an article once which included a photo of Dr. Mu. It was about the Grebe Mu-1 Synchrophase radio. When I studied it, I focused on the frequency response of the audio inter-stage transformer . In any case here is the article on the radio and remarks about Dr. Mu:

http://worldphaco.com/uploads/THE_GREBE_MU-1.pdf


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 Post subject: Re: TRF HOMEBREW RADIO
PostPosted: Jan Fri 17, 2020 8:07 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 35168
Location: SoCal, 91387
It is very interesting, and I like how you mounted the batteries to the underside of the PCB, clever idea!

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 Post subject: Re: TRF HOMEBREW RADIO
PostPosted: Jan Fri 17, 2020 5:00 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3946
Eye candy, for sure! I love the simplicity and direct effectiveness. The attention to detail, even to nickel plated brass screws is lauditory and speaks to a commitment to quality.


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 Post subject: Re: TRF HOMEBREW RADIO
PostPosted: Jan Sat 18, 2020 5:09 am 
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Joined: Jun Sun 15, 2014 5:37 pm
Posts: 466
Location: Montreal, Quebec
The first time I think I saw something about the LM372 was in the November 1972 issue of "73" , an article about using it as a AM BCB TRF. I always thiught it was designed for that purpose, but I dug out tte article lastnight, and it starts with mentioning it was intended for use in an IF atrio. Odd what we forget and remember, I even thought the article was written by someone at National, but apparently nit.

The articke does mention that tye IC can be used up to at least 7MHz, so it couid be used for some shirtwave, as long as it's AM. The detector diode is in a feedback loop for least distirtion.

So I dug out my National Semiconductor databook from around then. That does say it was intended for "IF or TRF use".

I think.by the time I saw the article in Nov 1972 I had already read about the Feranti ZN414 TRF IC, which maybe influenced my remembrance.

Other than the article, I don't remember other articles that used the LM372, wait I think an article in "Ham Radio" about a 160M receiver where it was the AM detector. I never saw mention of it in a commercial receiver.

It was an odd time, various companies coming out with ICs for. AM broadcast receivers but I never heard of them used in actual designs. The LM372 took care of some things, but other ICs put more of the receiver in the IC. RCA had the CA3088, but it too was limited to AM, less useful for shortwave. National had the LM373 which was just an IF strip, but could detect AM, FM and SSB/CW. Later AM receiver ICs were better, easier to use


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 Post subject: Re: TRF HOMEBREW RADIO
PostPosted: Jan Mon 20, 2020 12:46 am 
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Joined: Aug Wed 26, 2009 1:50 am
Posts: 1483
Location: Mesquite NV 89027 (from Coventry, UK)
Superb construction.


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