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gsparksPosted - 22 June 2013 20:23  Show Profile  Email Poster  Edit Message
Typing mistake, antenna was 30 foot, not 30". When I put the TV antenna up, on FCC spec 12 foot tower, I nyetied a 3' piece of PVC diaginal to beam on TV anenna then ran wire through it, and let han over eves and placed feedpoint at bottom of the window by radio and ground point. When I first used it with Baldwin C's laying on nightstand my wife would complain about the noise but she couldnt make it out when she ironed my clothes. That was when I used megaphone and telephone handset. so she could read audio.
BTW mentioning Hurricane ready, if anyone has battery portable TV, unless it's hd or converterwith battery, won't be of use, No analog TV will be turned on no matter what. The recommended solution given to me by local meteorologist was Laptop with USB HDTVtuner. sorry for rambling
Garry NicholsPosted - 23 June 2013 6:41  Show Profile  Email Poster  Edit Message
homebrew (or anyone);

Do you happen to know how the thick/thin spacers changed the audio characteristic of the headphone?

I just googled but only came up with modern headphone info.

TNX,

Garry

homebrewPosted - 23 June 2013 9:8  Show Profile  Email Poster  Edit Message  
Wide spacing gave louder code dots and dashes with a lot less fidelity.
Instructions for the Brownlee adjustable headphones said to start with the diaphragm touching the coil magnet and then slowly adjusting it until the magnet released the diaphragm. Then carefully adjust for maximum sensitivity.

Edited by - homebrew on 6/23/2013 9:30:57 AM

Edited by - homebrew on 6/23/2013 12:50:19 PM

_J_Posted - 24 June 2013 0:51  Show Profile  Email Poster  Edit Message
I can notice 3 dB (on sound mixers) if I really pay close attention. I can't really notice 2 dB and it takes 4 dB to be what I view as 'easily noticable' for me.

John Davidson

gzimmerPosted - 24 June 2013 1:24  Show Profile  Email Poster  Edit Message
> If they are real far apart you might get all 3 dB. Will that be noticeable?

Yes it will, 3db change is generally considered to be the minimum discernible change.

So in that sense, a 3db increase is the minimum which would be worthwhile.

To get double the apparent volume you need an increase of 10db.

......... Zim

Edited by - gzimmer on 6/24/2013 1:29:47 AM

golfguruPosted - 24 June 2013 2:40  Show Profile  Email Poster  Edit Message  
An extra 3dB RF might result in a greater than 3dB improvement in resolved audio, due to improved diode efficiency.

................

gzimmerPosted - 24 June 2013 5:13  Show Profile  Email Poster  Edit Message
But this is with separate diodes rather than one combined diode.

Being a bit picky, I know...

....... Zim

golfguruPosted - 24 June 2013 17:10  Show Profile  Email Poster  Edit Message  
Point taken.
Almost comes back to the point that it's probably easier to build a single antenna higher, and either longer or with multiple horizontal runs?

.............

Edited by - golfguru on 6/24/2013 6:36:39 PM

_J_Posted - 24 June 2013 21:50  Show Profile  Email Poster  Edit Message
Believe me, 3 dB aint gonna be worth it. If your payoff is to get 3 dB, you'd be better off to just stay on the couch and drink a beer.

And I agree with you GG.

John Davidson

Edited by - _J_ on 6/24/2013 9:59:22 PM

Garry NicholsPosted - 25 June 2013 6:34  Show Profile  Email Poster  Edit Message
John;

3 dB ain't worth goin' afta? It would seem that it is when on the edge of copy/no copy.

I don't have empirical experience but my readings over the years lead me to believe that 2 dB or greater in radio communication was worth going after.

Have the numbers changed as technology and testing methods have evolved?

TNX,

Garry

RichardPosted - 25 June 2013 8:37  Show Profile  Email Poster  Edit Message  
"Almost comes back to the point that it's probably easier to build a single antenna higher ..."

I agree. In my experience with AM band commercial radio station towers and the historic 1200 foot tall NSS VLF antenna at Annapolis, Maryland - higher antennas will deliver significantly more energy to a crystal set. So much more that a 40 db inline attenuator was required ahead of a modern communications receiver with the NSS antenna. To describe the unattenuated signal as an overload would be an understatement.

After optimizing crystal set architecture and component efficiency a higher antenna is the only way I know of to increase low signal level sensitivity without an amplifier. It's the radio analog of using a larger telescope to collect more light. Same difference.

Edited by - Richard on 6/25/2013 8:43:28 AM

homebrewPosted - 25 June 2013 11:26  Show Profile  Email Poster  Edit Message  
A higher and longer antenna is not a budget option for most of us that have already made the most of what is available over the years. I occasionally add a 50 ft vertical balloon antenna to my longwire. That is the max I can safely use and be sure to avoid the power lines.
All of the "little" set improvements add up and are worthwhile. And the experimenting is fun when I can find the time.
_J_Posted - 26 June 2013 2:12  Show Profile  Email Poster  Edit Message
Hi Garry,
I guess two dB is worth going after for some digital demodulation schemes because digital thresholds are not logarithmic like the ear. Our ear needs to transduce a huge range of levels into thoughts. Gain is controlled for digital demodulator and you can make its sensitivity curve anything you want.

Make any sense?

John Davidson

_J_Posted - 26 June 2013 2:15  Show Profile  Email Poster  Edit Message
Well thats a good point HB, if you get enough 2 dB improvements all lined up, that is something to get excited about.

John Davidson

gzimmerPosted - 26 June 2013 4:47  Show Profile  Email Poster  Edit Message
I wonder if Michael (mgschwartz) ever found the radio project book he was looking for?

........ Zim

Edited by - gzimmer on 6/26/2013 4:53:21 AM

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