[Lowfer] simple am loop antenna

[Ron Barlow]

> Date: Sun, 3 Jan 2010 21:30:53 -0500
> To: prosolar at sssnet.com; glowbugs at piobaire.mines.uidaho.edu
> From: brad.thompson at VALLEY.NET
> Subject: Re: GB> simple am loop antenna
> 
> At 10:28 PM 1/2/2010, Mike Bryce wrote:
> >Boys and girls!
> >
> >I'd like to listen to some plain old AM longwave on one of mine 
> >shortwave receivers.
> >
> >Really don't want to use a loop, I don't want to use an outside wire 
> >as I have too many wires flying around now.
> >
> >Would a wire just wrapped around some PVC pipe several feet square work?
> >
> >I'm thinking of using a frame made of plastic pipe and wrap the wire 
> >around the perimeter.
> >
> >Doable or am I'm barking up the wrong tree?
> >
> >mike
> **********
> Hello, Mike--
> 
> Some years ago [1], I built and described a loop antenna that 
> comprised an 18-inch circular
> wooden embroidery hoop, a 60-inch length of 14-conductor ribbon 
> cable, a crossover board,
> and a two-section variable capacitor salvaged from a defunct AA-5 receiver.
> 
> The wooden embroidery hoop has two sections-- an inner hoop and a 
> concentric outer hoop.
> The ribbon cable gets sandwiched between the two hoops, and short 
> lengths of double-sided
> sticky tape hold the ribbon cable in place.
> 
> I connected 13 of the ribbon cable's wires in series (i.e., the 
> "finish" end of wire 1 goes to the
> "start" end of wire 2, etc.). The "start" of wire 1 goes to the 
> variable-capacitor's higher-capacity
> stator plates, while the "finish" end of wire 13 goes to the variable 
> capacitor's rotor. The stator
> plates of the smaller rotor section go to a SPST switch that connects 
> to the higher-capacity
> stator.
> 
> The ribbon cable's 14th turn connects to the receiver's "antenna" and 
> "ground" terminals via
> a common-mode choke comprising six turns of AWG #34 bifilar wire on a Fair-Rite
> 2843002402 balun core.
> 
> The common-mode choke minimizes hand-capacity effects encountered 
> when adjusting the
> variable capacitor.
> 
> The SPST switch adds extra capacitance to permit tuning the upper end 
> of the LF beacon
> band and the lower end of the AM broadcast band.
> 
> If the receiver you're using has no antenna and ground terminals, you 
> can position the
> external loop antenna near the receiver's built-in loop or ferrite 
> loopstick antenna and use
> inductive coupling to improve AM reception. The combination will 
> exhibit relatively
> sharp directivity, so you'll need to rotate the receiver and loop. A 
> "lazy Susan" turntable
> may do the job.
> 
> Adding this (or indeed, any) external loop antenna provides an 
> impressive performance boost
> to an AM receiver-- even a cheap pocket radio will show greatly 
> improved selectivity and sensitivity.
> 
> When compared with wrapping magnet wire around an X-shaped frame, 
> using ribbon cable
> eases assembly, and especially so if you use mass-termination DIP 
> plugs on the cable's ends
> and fabricate a small PC board for the crossover connections. You can 
> also simply solder
> the wire's ends together as outlined above. For my prototype, I used 
> two DIP sockets and
> wire-wrapped the crossover connections.
> 
> 73--
> 
> Brad AA1IP
> 
> [1]: "AM Broadcast Band Loop Antenna", by Brad Thompson, Modern 
> Electronics, September 1987,
> pp. 56-64
> 
> 
> 
> 
> 
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