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 Post subject: Aircraft band radio question
PostPosted: May Fri 27, 2022 8:07 pm 
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Location: Kingsford Michigan
I recently gotten a Regency Flight Monitoradio model number AR -136 to listen in the local air traffic. There is a ton of homebuilt antenna plans available, one is built around a so-239 connector,my question is what type of coaxial cable to use.since this set has two wire terminal strip on the rear. Also is length critical for peak operations. This is really a nice set, it has a power transformer, original tubes, and clean chassis and cabinet. I'm thinking it wasn't used much, thanks for looking!


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IMG_20220527_135242399_HDR~2.jpg
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 Post subject: Re: Aircraft band radio question
PostPosted: May Fri 27, 2022 8:29 pm 
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RG58 or 59 should be fine. A random length of wire attached to terminal 1 should give you an easy way to get the radio on the air.

Rich


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 Post subject: Re: Aircraft band radio question
PostPosted: May Fri 27, 2022 9:22 pm 
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A simple quarter-wave whip made from an SO239 socket with each leg 24" long will be right in the middle of the aero band - 125MHz - 75ohm coax cable down to the radio - connect the centre conductor of the cable to #1 and the braid to #2 - this will match the 75 ohms of the antenna.

The old TV rabbits ears antenna would work too.

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 Post subject: Re: Aircraft band radio question
PostPosted: May Fri 27, 2022 9:35 pm 
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Location: Billings, MT
A diffetent option is to check out www.liveatc.net. Listen to any ATC freq in real time. No antenna needed. I often listen to the local tower and approach control freqs while putzing around in the shack.

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 Post subject: Re: Aircraft band radio question
PostPosted: May Sat 28, 2022 9:23 am 
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Greetings to ballroad and the Forum:

If you are going to construct a VHF ground plane antenna as in the illustration below, you will find that its characteristic impedance is closer to 50 ohms rather than 75. I would use RG-58 coax.

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VHF Ground Plane.jpg
VHF Ground Plane.jpg [ 307.8 KiB | Viewed 719 times ]


The antenna itself is constructed on an SO-239 female UHF panel connector and the feed line is connected using a PL-259 male UHF connector. Unless you live in an extreme desert environment, you will need to weather-proof both connectors... otherwise the coax becomes a water hose connected to your receiver. majoco's element length dimensions are about right.

Good Luck,

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 Post subject: Re: Aircraft band radio question
PostPosted: May Sat 28, 2022 9:49 am 
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Thank you for your help, very good information,!

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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 2:23 am 
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Do you intend to use an antenna indoors or out? A vertical dipole with each leg 26 inches fed in the middle with coax would work OK inside maybe. Depends on how far you are from any airports locally. Although high altitude planes are obviously easier to hear at a distance. Put spade lugs on the coax and connect it as stated on the back label.

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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 3:50 am 
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Greetings to ballroad and the Forum:

For that matter, since the radio has screw terminals on its input, it might want to see 300 ohms. In which case, a folded dipole made out of twin-lead would be ideal. Look up "folded dipole" on the internet to see how one is made; the length (in feet) is given by 468 divided by the frequency in MHz.

Regards,

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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 4:42 am 
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Location: Colorado Springs, CO 80917
Quote:
since the radio has screw terminals on its input, it might want to see 300 ohms


The cover is labeled for coax connections. Is there 300 ohm coax? Or do you suspect the design is mismatched the input for common coax but they kinda said "the heck with it, let 'em use coax, too"?

EDIT:
Schematic is here:
https://antiqueradios.com/forums/viewto ... 8#p2243398
Looks like it's designed for a low impedance input.


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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 5:09 am 
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hwhall wrote:
Quote:
since the radio has screw terminals on its input, it might want to see 300 ohms


The cover is labeled for coax connections. Is there 300 ohm coax? Or do you suspect the design is mismatched the input for common coax but they kinda said "the heck with it, let 'em use coax, too"?

EDIT:
Schematic is here:
viewtopic.php?p=2243398#p2243398
Looks like it's designed for a low impedance input.


I don't have access to the radio or the cover.... or until you posted the link, not the schematic either. How would I know that?

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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 5:32 am 
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Quote:
I don't have access to the radio or the cover.


It was in the first photo posted. BTW, I hope my previous post didn't get read as being snarky, but looking back on it, I can see that it might have sounded that way.


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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 6:09 am 
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Greetings to hwhall and the Forum:

Obviously, I didn't scroll down far enough to see the back cover in the photo and equally obviously, I misinterpreted your post. My bad; please accept my apologies.

Regards,

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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 12:18 pm 
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Not sure but I wonder if the reply from the OP indicated he was finished considering this thread?

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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 12:35 pm 
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Well actually, no still following, I always read what others contribute. In fact I saved the post from Stan the Man's as it contains a schematic also. Right now I'm using it in my garage as the weather finally came around. I will be recapping it soon, but it really doesn't buzz at all. I have a length of rg-58 coming and a couple of so 239 connectors. I
just wanted to experiment with antennas and such. Eventually it will sit on the mast on my house. Been doing a lot of research and I found very little on the schematic and general information. Please keep it coming,!

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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 2:21 pm 
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Does anyone really believe that a receiver of that caliber would have a defined impedance over its operating range??? Let alone the antenna...

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 Post subject: Re: Aircraft band radio question
PostPosted: May Tue 31, 2022 2:35 pm 
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No. It's like endless inexpensive receivers. It probably uses the terminal strip because it was cheaper than a UHF connector.


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