 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
71.212.141.20
Hi everyone! I bought a tiny tuner circuit board off of E-bay for a kitchen sound system. This one:"DSP & PLL Digital Stereo FM Radio Receiver Module 87-108MHz with Serial Control". $7.29 plus shipping. I am powering it from a 9 volt battery and an LM 7805 regulator to get 5 volts. It feeds a mini chip amp from Parts Express. Quite amazing for its size and price. I have a question about the antenna. It has only one hole for an antenna wire. The "documentation" says to use a wire about 75 cm with it. Is this a "tuned" length or is the wire length arbitrary? Is longer better? Should I be using NOS Western Electric telephone wire recovered from Area 51 and treated with ground diamond dust and ferret urine? ;) What do you think?
Follow Ups:
Ferret urine on helps at the commercial right side of the dial. The far-left channels you listen to in the SF Bay area require organic almond milk to bring in the signal loud and clear. Good luck with that.
"Writing about music is like dancing about architecture." ― Thelonious Sphere Monk
Cpwill
Just a follow up. Most of the stations we listen to happen to be clustered at the low end of the FM scale. I trimmed the wire to 75 cm and lost most of the stations at that end, but the stations in the middle of the band came in fine. I then used the frequency wavelength calculator to find the 1/2 wave length for 91.9 mhz, which is a station we listen to often, and it came to 64.25 inches. I soldered a wire of that length in, and now we have great reception of our usual suspects. Haven't tried the other end of the band yet. Thanks to everyone who responded. I love learning something new, and AA is a great place for that.
Wavelength = Speed of Light / Frequencythe speed of light is about 3 x 10^8 meters per second.
Do the maths :) -- or -- use a calculator (like the link below)E.g., for a frequency of say, 100 MHz (100 x 10^6 sec^-1):
wavelength = (3 x 10^8 m/sec)/(100 x 10^6/sec) = 3 meters
...so...
Yes, that recommendation is for a tuned antenna, sort of. To wit:
75 cm is approximately 1/4 wavelength at 99.9 MHz... which is reasonably close to "midband" in the US/European FM standard (88 to 108 MHz, give or take).
Radio circuits operate on "resonance" and thus do indeed work best (or 'work at all') for certain 'magic' combinations of frequency, component values, and antenna parameters. In terms of antennas, multiples of 1/4 wavelength are 'good' for transmission (or reception), although 5/8 wavelength antennas are also common (I don't know why!). Multiples of full wavelengths are good, too (note the options on the calculator link below).
IF you have a specific frequency you want to use, you can (and, arguably, should ) make a 'tuned' 1/4 or 1/2 wavelength antenna. It "should" :) work nominally better than a random length of wire.
For example: suppose you want to transmit on 94.3 MHz. 1/4 wavelength = 79.53 cm or 1/2 wavelength = 1.59 meters
HTH (hope this helps), as they say!
all the best,
mrh
Edits: 08/15/19
Any difference accomplished by trimming that wire to its theoretically resonant length will be hit or miss. A 1/4 wave vertical requires a ground plane in order to be effective. Not only does the home tuner not provide a ground plane, the tuner chassis and AC wiring length represent the other half of a badly skewed and non-resonant dipole opposite the single wire. If you could ground the chassis of the tuner directly to a short, low resistance earth ground, the single wire could be tuned to resonance with the formula. Otherwise, it's likely not worth the bother.
--------------------------
Buy Chinese. Bury freedom.
I once went to the trouble to bury two long ground wires in a triangle under my random length, tuned, AM BCB antenna, feeding a wide-band-audio AM stage.
One wire made things noticeably quieter but not a lot, two were a waste of effort. But, they re still there and might be of use when I put an enclosed active toroidal looped item on the mast.
? The random wire broke and I'm banned from climbing ladders.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Cool! Thanks for the info. Gotta get out my tape measure.
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
