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 Post subject: A way to use U.S. Navy RU receiver ?
PostPosted: Sep Thu 19, 2019 10:16 pm 
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Joined: Mar Sun 14, 2010 2:51 am
Posts: 472
Location: Newport, Oregon, 97365 U.S.A.
The U.S. Navy aircraft receiver type RU was used in various versions from late 1930s thru 1940s. This is a TRF receiver
with this plan: 3 x RF, detector, AGC amp, BFO, and one audio. There are only 3 tuned circuits at frequency and you can imagine how well that works out on HF. That means this receiver "can't get no respect" among hams today; it's considered unusable with no practical way to improve selectivity without a multi-control external box, like for regeneration and frequency adjustment. Not considered viable for an authentic aircraft setup.

But I thought about this: the detector is a biased power detector with about -13 volts on grid, compared to about - 3 on the RF amp grids. What if you lower the detector bias so it operates in linear mode, as a product detector? Followed by a roll-off audio filter for about 2500 Hz low pass. Then your selectivity is defined by the audio response, instead of the AM detector response of 50 or 100 kHz
bandwidth. With this change, you always have to have the CW osc on, so you have to zero beat an AM signal, but at least now the receiver is usable on the ham bands, right?


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 Post subject: Re: A way to use U.S. Navy RU receiver ?
PostPosted: Sep Sun 22, 2019 2:42 am 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 9921
Location: Ohio 45177
I am not clear here. I thought that product detectors were kind of a second mixer as it were, creating the mixing product from the BFO and the received signal. As for it being a TRF radio, the best thing I can imagine would be to use it as an IF after a converter, at about it's lowest operating frequency to maximize it's selectivity as an IF. But not being familiar with the radio, I cannot guess at it's potential. You may have a true boat anchor radio.

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 Post subject: Re: A way to use U.S. Navy RU receiver ?
PostPosted: Sep Sun 22, 2019 7:41 am 
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Joined: Mar Sun 14, 2010 2:51 am
Posts: 472
Location: Newport, Oregon, 97365 U.S.A.
It has only tuned stages at frequency. You can imagine this is unusable at 4 MHz. Even at the lowest frequency, about 200 kHz,
people report that the 3 tuned stages are not enough for use in a hamband. The product detector has its output limited to the audio bandpass. Yes, so far a real anchor, but maybe there is hope.


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