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Author Topic: Audio quality and antenna suggestions  (Read 9530 times)
Chadan
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« on: February 29, 2012, 08:08:24 PM »

Hi Scanners. I have an old Lloyd's analog tuner with a 5' whip antenna and the audio quality from it seems better than the audio from my brand new BC125AT scanner. I'd love to use the scanner as my feed, but don't want to sacrifice audio quality.

I built an antenna (details in my KAMW post) but think I'm doing something very wrong. Maybe the coax I chose is lossy? Tips on getting a digital scanner to sound as good as a ~30 yr old analog scanner much appreciated!
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Feed provider for KBNW out of Boone, Iowa on 123.0. Also catching chatter from nearby airports: KAMW (122.7), KIKV (122.9) and the Aviation Guard channel (121.5)
K5PAT
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« Reply #1 on: February 29, 2012, 10:18:37 PM »

Chadan,
     Are you comparing the two audios over the internet or are you just listening to the local speaker outputs?  The speaker size and audio power output should be better on the LLoyds since it is a larger "base" unit.  However, once the audio goes through your computer it gets digitized and converted back to analog when listening to it over the internet, so there should be little difference between the two radios, unless you have hum or audio distortion on one of them.
     If you have a set of headphones, you might try listening to the audio using them and then compare the two radios.  That will eliminate any speaker and audio power output differences.
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Chadan
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« Reply #2 on: February 29, 2012, 10:23:10 PM »

Hi K5PAT. I'm listening to the result after it gets fed through LiveATC.net. One of my digital scanners has a very noticeable hum while the other just doesn't seem to pick up nearly as much traffic.
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Feed provider for KBNW out of Boone, Iowa on 123.0. Also catching chatter from nearby airports: KAMW (122.7), KIKV (122.9) and the Aviation Guard channel (121.5)
K5PAT
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« Reply #3 on: February 29, 2012, 10:39:36 PM »

Which scanner are you using now?  I am listening to hum now.
Can you run it from batteries or a DC supply to eliminate any AC hum problems?
Did you try to bypass the electrolytics in the power supply?
Did you try grounding the computer to the scanner with a jumper lead?
The LLoyds is probably not going to be as sensitive or selective as the RS handheld. It is an older unit and is not tuned specifically for the aircraft band.  The RS unit is new and probably has a much more sensitive receiver and is crystal (PLL) controlled which make it more stable.

I am using the same RS scanner (PRO-164) on my ZHU feed and I still can't get out all of the hum, but I got it down to manageable levels
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K5PAT
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« Reply #4 on: February 29, 2012, 10:51:47 PM »

As far as the antenna goes, I would stick to the time proven 1/4 wave ground plane.  Use the formula  234/freq. in MHz.  It will give you the vertical radiator length in feet.  Use 5% more length for the radials.
 For 125.5MHz I get 1.87 feet or 22.44 inches.
The radials are 23.57 inches.

Use good 50 ohm coax cable, either RG/58 if under 30 feet, or RG/8 type if over 30'.
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Chadan
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« Reply #5 on: February 29, 2012, 11:36:35 PM »

Thanks a lot for the specific suggestions K5PAT! I'll try to eliminate the AC power supply to see if that's contributing to the hum.

Attached is a 3 minute clip of my ASOS:

First 30 seconds: Lloyd's; Next minute: RS Pro-97; Next minute: BC125AT; Last 30 seconds: Lloyd again.

Maybe if I just have Dave boost the signal the BearCat could work if the signal's clean enough.
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Feed provider for KBNW out of Boone, Iowa on 123.0. Also catching chatter from nearby airports: KAMW (122.7), KIKV (122.9) and the Aviation Guard channel (121.5)
K5PAT
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« Reply #6 on: March 01, 2012, 01:42:03 AM »

I think I know why the LLoyds sounds better. The old multi-band broadcast radios had a wide bandwidth in order to receive HF AM broadcasts in "High Fidelity".  The bandwidth of the LLoyds is probably 50KHz or more. That's why it sounds more "Hi-Fi". Unfortunately, it will also receive signals on either side of the "tuned-in" frequency due to the wider bandwidth.  It does sound better than the others, but they all have some hum. 
    The newer scanners sound "more tinny" since their audio bandpass is somewhere around 300-3000 Hz, whereas the LLoyds is probably 100-10,000 Hz.
     The scanners sound OK, just like two-way radios sound today, but they still have the hum and sound "noisy".
     If you can add a pre-amp in front of the LLoyds and get the antenna fixed, it will probably be the one I'd choose.
     Right now at 12:40 AM CST the hum is very acceptable, but I only hear weak unreadable signals.
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Chadan
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« Reply #7 on: March 01, 2012, 08:01:46 AM »

Last night after recording the above sample of all three I decided to leave the RS Pro-97 in place. Mostly what it's picking up is 126.0 clearance delivery from Des Moines, ~30 miles south of my position. I agree that it sounds unintelligible.

I'll leave it in place for a little bit to see if I can catch local traffic any better. Might remove 126.0 from the scanned frequencies since it's so scratchy.

I'd like to build a Yogi antenna but don't see plans for anything less than several meters long which is too obstructive for my small apartment. Can the dimensions be trimmed down to 1/4 size with any effectiveness? Looking on a site Dave referenced  (http://www.wa5vjb.com/) I don't see anything in the 118-136 MHz range. Maybe their product line changed.
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Feed provider for KBNW out of Boone, Iowa on 123.0. Also catching chatter from nearby airports: KAMW (122.7), KIKV (122.9) and the Aviation Guard channel (121.5)
K5PAT
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« Reply #8 on: March 01, 2012, 10:25:59 AM »

Go to this posting from Dave:
  http://www.liveatc.net/forums/listener-forum/airband-yagi-antenna-designs/

In Dave's first posting, click on the pdf at the bottom of the post (vjb-airband.pdf). It describes how to build an airband yagi.  I am using one like this on my ZHU feed and it is doing pretty well picking up a distant Houston Center site.
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Chadan
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« Reply #9 on: March 01, 2012, 11:29:55 AM »

Thanks K5PAT. I read the posting and saw mention of a PDF but failed to find it until you spelled it out!
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dave
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« Reply #10 on: March 01, 2012, 03:30:11 PM »

If you don't want to build you can purchase one from Arrow Antennas:
http://www.arrowantennas.com/arrowii/arrowii.html

Don't forget the mounting bracket:
http://www.arrowantennas.com/main/mbii.html


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Chadan
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« Reply #11 on: March 01, 2012, 03:39:15 PM »

Thanks Dave! I was interested at $55, but $15 in shipping is pushing it. I'll see if I can make sense out of the PDF.
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Feed provider for KBNW out of Boone, Iowa on 123.0. Also catching chatter from nearby airports: KAMW (122.7), KIKV (122.9) and the Aviation Guard channel (121.5)
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« Reply #12 on: March 01, 2012, 03:45:19 PM »

Building one is more fun anyway!
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Chadan
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« Reply #13 on: March 01, 2012, 03:47:42 PM »

 grin
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Feed provider for KBNW out of Boone, Iowa on 123.0. Also catching chatter from nearby airports: KAMW (122.7), KIKV (122.9) and the Aviation Guard channel (121.5)
Chadan
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« Reply #14 on: March 05, 2012, 04:42:36 PM »

I built myself a Yagi! It was really simple following the PDF linked to above. I think the reception is better - at least I can get ground conversation pretty well. I did lose some clarity from aircraft at altitude, but that was expected since this is a directional antenna. Pics attached.

First pic is looking up the beam. It isn't installed this way - it was just easier to photograph. It's installed with the beam pointing horizontally toward the airport and the antenna are vertical. Yes, that's my t-shirt tail from my first solo in the background  grin

Second pic shows coax connections. I found the braid from RG-6 (which is the wrong type but all I could find) is impossible to tin even with flux, so I couldn't solder it. Used an aluminum crimp connection instead. It'll remain indoors so this should last years. The center electrode soldered nicely onto the brass rod and there is approx 1/4" air-gap between the rods inside the beam.

Third pic is just 1/8" brass tubing with the next smaller size telescoped inside of it. Figured it was cleaner than cutting and lashing same-size tubing together. I just happened to have it left over from my failed $20 SO-239 antenna.
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Feed provider for KBNW out of Boone, Iowa on 123.0. Also catching chatter from nearby airports: KAMW (122.7), KIKV (122.9) and the Aviation Guard channel (121.5)
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