[time-nuts] Antenna

Bob Camp kb8tq at n1k.org
Tue Jul 8 19:20:37 EDT 2014


Hi

You can spend *way* to much time analyzing these gizmos. The simple approach is (almost) always better:

1) How much room do I have?
2) How high can I get it? 
3) What sort of coil form is available cheap?
4) How much inductance is in a few turns?
5) What frequency(s) am I interested in?

Simple math will tell you if the inductive reactance is > 50 ohms. If so, you need a transform(er) of some sort. A high-z amp is one way to transform the impedance. 

Wind it up and give it a try…

Bob


On Jul 8, 2014, at 6:17 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:

> In message <53BC56FC.3030909 at rubidium.dyndns.org>, Magnus Danielson writes:
>> Hej Poul-Henning,
>> 
>> On 07/08/2014 09:59 PM, Poul-Henning Kamp wrote:
>>> In message <53BC4B9F.6040302 at rubidium.dyndns.org>, Magnus Danielson writes:
>>> 
>>>> I have a FS700 sitting here, but no antenna. There should be other
>>>> signals than LORAN-C/CHAYKA available, such as DCF77, MSF60 and the 162
>>>> kHz signal from outside Paris. It would be pretty straight-forward to
>>>> put up a frame and make a number of turns of wire, and put a low-noise
>>>> amplifier up in the attic. What existing projects should I look at or
>>>> take inspiration from?
>>> 
>>> http://phk.freebsd.dk/loran-c/Antenna/
>> 
>> What is your loading on the coil? How many turns? Schematic?
> 
> No loading, I wanted flat frequency response.
> 
> No ideas how many turns, it's not critical.
> 
>> Cooking up a low-noise amplifier for these frequencies seems relatively 
>> simple, but it is always nice to see what others have done.
> 
> I just winged it, I looked at the stuff at VLF.IT then the AD797
> data sheet and when it worked well enough I stopped.
> 
> I have also built a "monopole" antenna, based on the schematic on page 6
> in this article by Chris Trask:
> 
> 	http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf
> 
> The performance is astonishing: it pulls in everything from the
> Schumann resonances and ~10kHz russian "Omega-like" naviagation to
> 100 MHz FM radio, but also every source of noise you can imagine
> in your neighborhood.
> 
> In difference from the loop which needs none, this antenna needs a
> really good earthing.
> 
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
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