Peter Chadwick wrote:
>
>
> So far the EWE seems to do what it is supposed to, although the noise
> is still bad. On it, the S/N on Bill, K0HA, was about the same as on the
> dipole, but of course the signal was weaker. The signals from Eu were
> much weaker. The loop still gave the best S/N. I'd suggest a tuned loop
> is worth a try, especially if there is a definite source for the noise.
>
> I'm wondering if a phasing system might help get the noise down. The
> problem is, I think, that there are multiple noise sources.
>
> I figured a possible route is to mix 160M up to VHF, use a phase shifter
> consisting of cascaded 90 degree hybrids with varicap terminations, and
> then mix down again ( using high dynamic range mixers, not NE602s!) This
> would make the phasing sections practically small, so several parallel
> paths could be incorporated to account for multiple sources. Has anyone
> any comments to make on this approach?
>
> 73
>
> Peter G3RZP
>
Peter,
You could try feeding both ends of the EWE (via 9:1 xfmrs) using similar
lengths of coax and then null steering for noise minimum. This is very
effective for noise cancellation off the back of the required direction
of EWE as well as making the system 2-directional. Simple c/o switch
between the two coaxes in the shack; with LCR and a small toggle switch
in series connected between the two coax centre input plugs. C=800pF
airspaced variable, L=22uH, R=1000R. I use this system on my 500ft E-W
beverage and it works well, also have tried on a single EWE with same
results. Tony G3OFW also uses the system.
At this location the beverages perform half to one S unit better than a
single EWE. Two EWEs spaced a little over 200ft in phase work similarly
to the beverage as you might expect. However, an effect I have noticed
is that the EWEs seem more susceptible to local noise - there could be
many reasons for this but have not fixed because luckily the continuous
noise source disappeared! All coaxes have chokes each end.
73's
John
G3PQA
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|