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 Post subject: UHF Crystal Radio
PostPosted: 26 Dec 2015, 08:11 
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Joined: 24 Sep 2014, 08:22
Posts: 68
Location: Bangalore, India
A crystal radio was wired up to check whether it could receive VHF/UHF signals in the vicinity of the shack.

No signals were audible, either in the shack or on the shack roof, using a 500 mm whip antenna.

However, a weak digital signal was detected with the sound powered phones, while moving on the shack roof using a 250 mm whip. Position on the roof and direction in which the whip was pointed were quite critical.

It was presumed that the signals were from a nearby cellphone tower. A 3 Element Yagi Beam for 33 cm was made using a broken snare drum stick for the boom and 20 SWG bare copper wire for the elements.

The coil was wound integral with the driven element. The same germanium diode and tubular ceramic capacitor were used.

The signal was much stronger with this setup and the beam pointing North-East.

Rgards,

Nandu.


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 Post subject: Re: UHF Crystal Radio
PostPosted: 26 Dec 2015, 16:11 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
So much digital chitter-chatter on UHF here, it sounds like an Electonica music track without a really selective front end :D

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 Post subject: Re: UHF Crystal Radio
PostPosted: 26 Dec 2015, 21:16 
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Location: Bangalore, India
Hi OM Gregg,

I also built the 900 MHz version of Harry Lythall's cavity receiver (http://www.zerobeat.net/g3ycc/cavity.htm) last week. It has a 250mm whip instead of the antenna BNC and a earphone jack for the phones.

I can tune in the digital signal but it is real weak. Wish I had used the BNCs and also built the Yagi earlier!

I'll have to rework it now and try it out with the Yagi.

Yes, digital signals are real musical.

Do check this out too.

http://www.kb9ukd.com/digital/

Many thanks.

73,

Nandu.

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 Post subject: Re: UHF Crystal Radio
PostPosted: 27 Dec 2015, 07:29 
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Location: Chilliwack, BC
vu2nan wrote:

Do check this out too.

http://www.kb9ukd.com/digital/


That's a good one. I had lost the bookmark, thanks for finding it again for me!

I submitted a few to him I head on web SDR for I.D. in the past, but no answer? :confused:

73's!

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 Post subject: Re: UHF Crystal Radio
PostPosted: 27 Dec 2015, 12:50 
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Hi OM Gregg,

Yes, it's a real good one.

73,

Nandu.

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 Post subject: Re: UHF Crystal Radio
PostPosted: 06 Jan 2016, 09:15 
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Location: Bangalore, India
Here's an update.

............Later on, another Yagi Beam was rigged up with a second OA85 providing the return path for the audio instead of the coil.

Signal strength was as good on that one too.

Regards,

Nandu.


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 Post subject: Re: UHF Crystal Radio
PostPosted: 06 Jan 2016, 13:34 
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Location: Chilliwack, BC
There was an article about 30-years ago in Radio-Electronics... they had a UHF crystal project, but had a pot to forward bias the diodes *just* before conduction to greatly increase sensitivity.

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 Post subject: Re: UHF Crystal Radio
PostPosted: 06 Jan 2016, 23:02 
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Location: Bangalore, India
Hi OM Gregg,

Here's how I bias foxhole radio blade detectors!

http://nandustips.blogspot.in/2013/05/f ... riant.html

73,

Nandu.

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 Post subject: Re: UHF Crystal Radio
PostPosted: 20 Jan 2016, 01:20 
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Joined: 24 Sep 2014, 08:22
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Location: Bangalore, India
Here's an update.

A folded dipole version, mounted on a terminal block.

Attachment:
4.JPG


Attachment:
3.JPG

It obviates the need for a coil / additional diode and works quite well too.

Regards,

Nandu.


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 Post subject: Re: UHF Crystal Radio
PostPosted: 20 Jan 2016, 13:49 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
Nice!

How do you get your wire antenna so perfect? Mine always look like a "coat hangar ran over by a car", hi, hi!

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