[Lowfer] Copper pipe loop question

[jrusgrove at comcast.net]

>There is no functional difference between this and a 10-turn loop of the same 
diameter. Same output voltage, same impedance.

Ahhh ... is this proof of the old total weight of the copper in the antenna ... 
whether fashioned as a one turn loop or in many turns ... not making a 
difference? Wonder if you happen to know the two different copper weights?

Jay W1VD





----- Original Message -----
From: John Andrews <w1tag at charter.net>
Reply-To: Discussion of the Lowfer \(US, European, & UK\) and MedFer bands 
<lowfer at mailman.qth.net>
To: <lowfer at mailman.qth.net>
Sent: 1/30/2025 2:14:20 PM
Subject: Re: [Lowfer] Copper pipe loop question


I agree with Jay on this one. The important thing is the concept of 
"broadband." I keep meaning to experiment with low-Z preamps, but have 
never gotten around to it.

On the other hand, if you are only interested in a narrow bandwidth, 
there are tricks you can play with a 1-turn tuned loop. Here at my home 
QTH in MA, I use a 5 foot diameter 1-turn loop made with 
1/2" soft-drawn 
copper tubing inside a piece of 1/2" i.d. PVC flex conduit 
(for rigidity 
and weather protection). It is connected to a 3:30 turn transformer made 
with an FT-140-77 core. That gives a 100X impedance step-up. At 185 kHz, 
where it is tuned to receive TAG from Maine, the transformer secondary 
shows 11 +j460 Ohms. There is no functional difference between this and 
a 10-turn loop of the same diameter. Same output voltage, same impedance.

After experimenting with series-tuning into a 1:2 transformer and a good 
50 Ohm preamp, I finally settled on parallel tuning into a preamp with a 
10k input impedance. A length of Ethernet cable uses 2 pairs in parallel 
for signal, and the other two for preamp power. Thus, the feeder back to 
the shack is balanced. Works great for its intended purpose.

And just one thought about 
J.B.'s plan to hang ladder-line across the 
transformer secondary -- that will set an upper-frequency limit due to 
the capacitance between the line conductors, which will parallel-tune 
the circuit. May not be an issue for LF, but would probably be at MF.

John, W1TAG





On 1/30/2025 12:32 PM, jrusgrove--- via Lowfer wrote:
> A 'small' single turn loop used as a broadband low frequency receiving antenna
> needs to be terminted in 'ideally' a zero ohm impedance amplifier ... not 50
> ohms ... in order to extract maximum available signal levels. Yes, his
> preamplifier uses a 1:40 transformer feeding the gate of the FET, but more
> importantly it also has a 1 turn winding from the source to ground coupled to
> the transformer. This winding provides current feedback and drives the
> amplifier input impedance to a very low level.
> 
> Jay W1VD
> 
> 
> 
> 
> 
> ----- Original Message -----
> From: John Bruce McCreath <weazle at hurontel.on.ca>
> Reply-To: Discussion of the Lowfer \(US, European, & UK\) and MedFer bands
> <lowfer at mailman.qth.net>
> To: wa3tts at verizon.net <wa3tts at verizon.net>, Discussion of the Lowfer (US,
> European, & UK) and MedFer bands <lowfer at mailman.qth.net>
> Sent: 1/29/2025 10:05:19 PM
> Subject: Re: [Lowfer] Copper pipe loop question
> 
> 
> 
> Hi Mike…..thanks for the link to the video. I watched it several times, pausing
> at the
> interesting points to take a better look at things. His toroid and secondary
> winding
> was especially so, and I finally heard the number of turns, which is close to
> mine!
> 
> I got a cheque in the mail today from our provincial government, trying to buy
> my
> vote in an upcoming election. I think I’ll spend some of it on the copper pipe
> and
> give my idea a go!
> 
> Tnx & 73, J.B., VE3EAR
> 
> 
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