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Help with 20-176 & Belden coax

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dorough

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I just bought a scanner today.... Radio Shack PRO-136. Yeah, I know it's a cheapy, but I don't mind. Obviously the stock antenna is pretty much crap. So I bought a 20-176, which folks seem to have a lot of good things to say about.

My goal is to monitor air frequencies including the control tower at an international airport which is about 5 miles away.

I've temporarily placed the antenna up on a rain gutter at the edge of the roof and run about 50 feet of Belden 1694A coax to it. That's a 75-ohm cable. I'm wondering if that's a problem or not.

I'm not getting good reception. I can hear airborne aircraft well, but can barely hear the tower transmission. I understand the line-of-sight issues. But other folks report great results using this antenna. The information with the scanner states to "always use 50-ohm coaxial cable, such as RG-58 or RG-8X. For lengths 50-100 feet, use RG-8X low-loss dielectric coaxial cable. For lengths over 100 feet, use RG8."

Is the Belden 1694A causing my problem?

Or do I need to "tune" the antenna... aim it?

Here's a link to the Belden 1694A.... https://edeskv2.belden.com/Products/#s=1694&r=0

Thanks in advance!
 
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n4yek

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The coax should not be an issue for reception of what you want to hear. The distance from the air field is something I believe is your issue here. You must remember, the control tower is talking to aircraft in the air and so their antennas will be oriented for just such purposes. I used to live about the same distance as you from an airport and barely received tower chatter with planes. If you are wanting to listen to them, a beam antenna would help you greatly.
Take care.
 

prcguy

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1694A is very good quality RG-6 used in the broadcast industry and should work at least as good as RG-8X. What kind of connectors do you have and who installed them? What's between you and the control tower?
prcguy
 

kb2vxa

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The main issue here is line of sight plus a little power vs. distance just to make life interesting. The control tower transmitter output is a mere 10W, the antenna relatively low to the ground as compared with other services located atop high structures and you have obstructions to contend with so don't expect much range at ground level. Aircraft on the other hand are at considerable altitude so you get a nice clear shot at them so to speak, I've communicated with spacecraft using as little as 5W into a simple ground plane antenna which gets me just a few miles to another Earth based station.
 

hertzian

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I just bought a scanner today.... Radio Shack PRO-136. Yeah, I know it's a cheapy, but I don't mind. Obviously the stock antenna is pretty much crap. So I bought a 20-176, which folks seem to have a lot of good things to say about.
That's exactly what I'm using my '136 for! While it is inexpensive, and may "look" somewhat like a toy, the basic radio is great. Triple-conversion, LOUD audio, sensitivity and construction seems ok. I was surprised at how smooth the volume/squelch pots are. Ok, no alpha-tags, but if you are listening to it across the room or from another room in the house, they won't benefit you anyway. :) The '136 makes a great scanner for general aviation for sure. If you organize the banks and not try to scan 200 channels all at once, you'll pick up a lot of action. I have the delay on tower freqs, and not on unicom stuff - personal choice.

It is also nicely portable, as the backup batteries for the clock will actually power the unit for a very long time - much like owning a handheld, but with awesome audio. 1100mw can drive that large built-in speaker pretty cleanly.

All the other comments are right on track - although take heart that for the most part the aircraft are going to be repeating back what the controller told them. So you won't miss out too much figuring out what is going on until you find a better antenna solution.

In the meantime, can you hear the tower *at all* if you walk around with the '136 in portable mode? You might find a spot around the yard or on the roof where you can at least hear it weakly - beats nothing at all. If I remember correctly, the whip that was included with the unit when fully extended is about 22-23 inches. Just about right for a general-aviation 1/4 wave whip - this will do for the walk-around.

Strangely enough, you might find a spot around your location that might not actually be that high - but in an area that allows for some sort of weak tower reception. When found, you could place the 20-176 there temporarily until you come up with something better. I'm betting no, but at least you could say you tried.

If the tower is not active when you are searching for a signal while portable around the house, you may also want to see if you can hear the ATIS frequency and walk around until you hear that. Perhaps disable the squelch at first. The problem here is that the atis antenna, power, and directivity may not match what is at the tower for regular comms, but it might help with the signal search.

The yagi is probably the best idea, but for now from a systems-standpoint, you gotta' work with what you've got. Don't be ashamed of the '136 - I'm not!
 
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dorough

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Update -

Well, I've mounted the antenna to a 3 ft. mast which I then mounted on my roof - a total of about 15' to the base of the antenna (18 ft' to tip.)

Using Google Maps, I determined that my house is 6.52 miles from the control tower with trees and a couple of neighborhoods in between.

Still no signal from the tower at all. Of course, aircraft come in loud and clear, but not a peep from the tower.

Does the orientation of this 20-176 antenna matter? How about the position of the three vertical radials (I suspect that's what they're called :) ) with respect to the three lower horizontal radials?

Or am I just out of luck?

I'm frustrated because I listen to Listen to Live Air Traffic Control Communications | LiveATC.net and someone has this particular airport already setup. Problem (for me) is that I want to listen to only the tower & ground, not approach, departure or center - as is the current setup on liveatc. But whoever that person is - they broadcast tower & ground crystal clear. Maybe it's a bit of tech-geek in me... I'm just frustrated that I'm not getting that same clear reception.

Ideas?
 

hertzian

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You'll definitely want to try a yagi beam at some point for tower and especially ground from where you are at.

I have quickly modified a few broken 20-176 antennas into pseudo-dipoles for VHF-AIR by removing the lower radials completely, and attaching 4 snap-on chokes (RS #273-105) about 23 inches down the coax. Of course you could just try without the chokes.

It isn't perfect, but might be worth a shot.
 

dorough

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Hey Hertzian - Do you mean just taking the three lower poles off will make the 20-176 better for air communications?
 

hertzian

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Jump off the table better? Not really. :)

My hope is that it will change your antenna from a groundplane to something similar to a dipole and that it might at least allow the tower to break squelch. It only cost a couple minutes to unscrew the three groundplane elements to try.

In my situation, I am finally able to hear a weak morse-id from a VOR with the groundplane removed, AND choked. I still have to have the squelch open to hear it, but when configured as the conventional groundplane, or without the chokes in the radial-less configuration - nothing is heard.

The nice things is that this was reproducable with a "classic" dipole fed with coax horizontally at the feedpoint. Without any chokes, nothing is heard. With the choke (in this case right near the feedpoint), the VOR station is heard once again with the squelch open.

For many this could be a costly experiment with 4 of the 273-105 chokes, but I have a few laying around from other projects, so the cost was nil.

So it may not solve your problem, but is a good way to recycle broken "sputniks", or hide them behind the drapes for single-band VHF operation.

BTW, if one did try the chokes, measure from the top of the metallic cone where the radials attach down about 22 - 23 inches, and place your chokes down from there.

I have a friend going through the same problem as you - he lives close by, but unless he raises his antenna 60 feet up because he is lower in elevation than the tower, he's pretty frustrated.
 
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