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 Post subject: UNUNs, lightning arrestors but for MW
PostPosted: May Sat 21, 2022 10:32 pm 
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Location: Bethlehem, PA
So my AM broadcast band options at my new place is terrible. If I plug in my lat & longitude into https://radio-locator.com/ it shows I have two "strong" local stations for my new zip code and that's it. Then to make matters worse, I live in the bottom of a valley surrounded by mountains. In a concrete & steel commercial building where the structural steel is grounded. It even has a metal roof. During the day I am lucky if I get *any* AM stations. During skip I can get the news out of Boston and the talk radio station in Reading and that's about it.

It makes fixing radios frustrating because I am always questioning how well they actually work until I physically take them off site to use them somewhere else. If they get my part15 transmitter inside the house good, then I know they're functioning, and then I align the sets, and still am lucky to get any stations.

Shortwave however is "okay."

So I constructed an untuned rotatable loop using 20 turns of 28 AWG on a 17x17 cross frame (so a 12"x12" loop). Its functional, as I can experiment with moving the transmitter further away to where I can normally barely recieve it, and use the antenna to find it and receive it. But its just not cutting it, so I think I need to build something outside.

From reading, I hear people recommending ~9:1 or even 10:1 UNUNs for AM/BC random length outdoor antennas. I have spent a few days looking at off the shelf 9:1 UNUNs and the ones that have performance graphs/curves show that they're miserable below 1 to 2 mHz depending on the product, which means I'd have about half the BC band not really taking any benefit from them. Does anyone know of a 9:1 UNUN (to purchase or build) that works efficiently down to 500 kHz?

The next problem, is I'd probably want a lightning arrester but I cannot find any with advertised specs below 1.8mHz. It seems that most (all?) made these days are catering towards hams because the idea of stringing 100ft of long wire between backyard trees for AM reception is decades past being on vogue. I don't need something for hundreds of watts of transmission power because I am just going to be using the antenna for reception.

I figure I can easily put a insulator on a guywire from the top of the chimney and have 150ft between there and the front of the building.


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 Post subject: Re: UNUNs, lightning arrestors but for MW
PostPosted: May Sat 21, 2022 11:02 pm 
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Location: Montvale NJ, 07645
sgath92 wrote:

From reading, I hear people recommending ~9:1 or even 10:1 UNUNs for AM/BC random length outdoor antennas.


What receiver are you using? Unless it has a low impedance input, you generally don't need the unun with a random length outdoor antenna.


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 Post subject: Re: UNUNs, lightning arrestors but for MW
PostPosted: May Sun 22, 2022 1:12 am 
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Joined: Apr Sun 15, 2012 3:10 pm
Posts: 1119
Location: Buffalo, NY
I don't have a copper telephone, so what I did is isolated all my phone jacks used for VOIP service, from the old copper demarc.
Clip on to one leg of the telco demarc in the basement with a cap & alligator test lead to some magnet wire. Ran the magnet wire
to my console & table top radios. Basically using the outdoor telco as an AM antenna.
Started out as just an experiment, but works pretty good, so I just left it that way.


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 Post subject: Re: UNUNs, lightning arrestors but for MW
PostPosted: May Sun 22, 2022 2:22 am 
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Location: Bethlehem, PA
I plan on using it with any and all of my radios, whichever one I feel like listening to at the time, so mostly 1930s radios, and occasionally a handful of ham receivers (nothing fancy, 1930s RCA offerings, my grandfather's WW2 BC-348, and his Hammarlund HQ-180). The HQ-180 is by far the newest thing I am likely to use, usually I don't stray from 1930s era stuff.

Building does not have any telecom lines at all, inside or out.


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 Post subject: Re: UNUNs, lightning arrestors but for MW
PostPosted: May Tue 31, 2022 9:48 am 
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A possibility?

https://www.okdxf.eu/lankford/Variation ... %20SWA.pdf

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 Post subject: Re: UNUNs, lightning arrestors but for MW
PostPosted: May Tue 31, 2022 3:35 pm 
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Location: S. Dartmouth MA 02748-1225 USA
sgath92 wrote:
I plan on using it with any and all of my radios, whichever one I feel like listening to at the time, so mostly 1930s radios, and occasionally a handful of ham receivers (nothing fancy, 1930s RCA offerings, my grandfather's WW2 BC-348, and his Hammarlund HQ-180). The HQ-180 is by far the newest thing I am likely to use, usually I don't stray from 1930s era stuff.[/quote
Quote:
]I figure I can easily put a insulator on a guywire from the top of the chimney and have 150ft between there and the front of the building.
therefore, using some sort of transmission line is an impossible lossy configuration for all bands...

Rum that 150', just be sure that the fixing to the chimney is most secure and at the far end as well. Use an insulated downlead all the way to the point of entrance. If the run can be made with bare wire that fine too. At the entrance to the building configure a lightning arrestor, easy homemade spark-gap, configure gap upwards so water does not short. run a ground wire to the nearest safe ground, should use a large gauge wire if practical.

If you own the building choices are yours but if your renting, careful...

The length of 150' will be a very strong pull on the wire, either use hard drown of decide to go a shorter length and make up with "antenna" rope. Do not solder connections, weakens wire, use electrician's bronze Burndy clamps. Coat with tar once connected.

You have your loop, place that next to your antenna entrance, bring the ground in too. Connect the antenna to the loop and the ground. The two connecting wires should not be more than 5 to 10 feet. The loop is an "aperiodic radiator", radios with internal antennas brought near should do well. For radios that require antenna and ground the loop can be disconnected and go direct.

If the loop has a parallel tuning condenser this will peak the circuit and increase the radiation but only in a narrow band.

Ideally, the radiating loop should be larger with greater spacing and larger wire. Try 18ga strand MTW, spaced 1/2" apart on a frame that encloses some 6 to 8 square feet. Large and ugly :roll:

GL

Chas

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 Post subject: Re: UNUNs, lightning arrestors but for MW
PostPosted: May Tue 31, 2022 4:23 pm 
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Location: Albion, CA, USA, 95410
Chas wrote:
sgath92 wrote:

The length of 150' will be a very strong pull on the wire, either use hard drown of decide to go a shorter length and make up with "antenna" rope. Do not solder connections, weakens wire, use electrician's bronze Burndy clamps. Coat with tar once connected.

Chas


I don't think you need hard drawn wire. I have over 550' of regular wire in a loop. It is fine stranded and tinned. Been up for years. Guys have worn out but the wire is fine. There are several soldered connections to join various pieces and no problem.


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