Topband: Low dipole for receiving

[Brian_ve7jkz]

Thanks John, interesting and encouraging.

Brian VE7JKZ


On 9/18/2013 7:54 AM, John Kaufmann wrote:
> I also use a low dipole, ten feet high, as a supplementary receiving 
> antenna.  It's a random length, not even resonant on 160.  I make no 
> effort at all to match it.  For receiving only, it's just not 
> necessary.  There is a lot of mismatch to the feedline, but unless 
> your feedline is very, very long where the mismatch would cause very 
> large feedline loss, you won't see any difference except for higher 
> signal levels with matching.  However, the SNR should be same with or 
> without matching because the noise floor is set by atmospheric noise 
> that comes in on the antenna.
>
> I find the low dipole often comes "alive" right at local sunrise and 
> allows me to hear and work DX stations (VK's, ZL's, JA's, etc.) that 
> are inaudible on my multi-element vertical receiving array.  The 
> difference is sometimes dramatic, but it only lasts for a short time.  
> The rest of the time, the verticals usually kill the dipole for receiving.
>
> 73, John W1FV
> On 09/17/13, Brian_ve7jkz<ve7jkz at telus.net> wrote:
>
> I've been looking at a very low dipole to hopefully assist in receiving.
> Living in suburbia space is limited but thanks to a helpful neighbor I
> could put up something in the shape of an L. I would have a 90ft
> straight length, then the feedpoint, then a 30ft straight length, a 90
> degree turn, followed by another 60 ft straight length. Total length of
> 180ft approx. Running along the top of the garden fence approx 6ft high.
>
> EZNEC 3 tells me that at 1.83Mhz the feedpoint impedance would be
> 0.65-j590, and at 3.52Mhz it would be 1.7+j510. How do I match it? I
> could always use a relay to switch in some L for 160m and some C for
> 80m, then a transformer to get to close to 50 ohms, then a high pass
> filter because I'm only a few hundred yards from a 50kW BC station on
> 690Khz, followed by a W7IUV amplifier.
>
> Is this a reasonable approach or is there a better/simpler way?
>
> Brian VE7JKZ
>
>
>
>
> _________________
> Topband Reflector