I do love the way the varied interests in this hobby are propagated through
this club from member to member and I'm grateful for the knowledge and
experience that's so freely shared.
One baby elephant in the room is Mark's antenna "ambience." If his QTH
there in the Land O' Goshen is in a field of electrical interference (and
perhaps significant local RF?), the noise gathered by the lead-in may be an
issue best resolved not by common-mode choking but by "balancing" the
feed-lines.
I've bored folks to death by espousing the balanced twisted-pair approach,
in the form of Category cable (Cat 5, Cat5e etc) with an impedance around
110 ohms. IMHO such a BALANCED transmission line pretty much eliminates
stray pickup without the need for common-mode choking. Cat-5 sells for
around $45/1000 feet...although if the budget allows, I'd go for STRANDED
Cat-5.
As I type this I'm watching the Perseus on a D-Kaz facing mostly west and
watching Seattle rolling in, here in North-Central Minnesota. Using a 9:1
transformer and Cat-5 with a DXE RPA-1 in the shack and watching a noise
floor of -111 dbm in 5 kHz, after the amplifier's 15 db gain.
An absolute YES to the Vactrol approach for the null component. The design
for that circuit somewhat obviates the potential for stray common-mode
pickup, so coax may work FB, but again...twisted-pair is so easy to
implement.
As to mounting the RF amplifier at the antenna: I've tried the FLG and the
DXE, planting them both at the antenna and in the shack. Like Don Moman, I
can't really find any significant improvement...though in theory
antenna-mounting of the amplifier is the better approach; weathering issues
notwithstanding. (You would however, need a balancing transformer after the
amplifier if you fed twisted-pair.)
A winterized installation at my site would include twisted-pair lead-ins, a
9:1 transformer and a Vactrol control, mounted in weatherproof boxes and the
amplifier in the nice warm shack. Amazon fans have found all sizes of
weatherproof boxes and wire feed-throughs:
At Amazon's greedy query, type in: "Cable Connect Waterproof Plastic Case
Junction Box" and "Plastic Waterproof Cable Connectors"
Decent transformers (if you don't have strong RF nearby)
http://www.minicircuits.com/pdfs/T9-1.pdf
Now for the famous YMMV <g> Have fun Mark; continue to share your
experiences!
Mark Durenberger, CPBE
-----Original Message-----
From: Mark Pettifor
Thanks for the advice guys - much appreciated!
I should also publicly thank Tim Tromp for getting me interested in the DKAZ
to begin with.
Mark
On 2016-10-06 10:02 pm, Nick Hall-Patch wrote:
Agreed. They do cost a fair amount (mind you the exchange rate with the
pound isn't bad right now), but are solidly built and work very well.
Money well spent.
Nick
At 22:17 06-10-16, you wrote:
I very strongly recommend the Wellbrook FLG100LN, They go right at the
antenna and replace your xfmr. Now what is picked up by the antenna is
amped 22 dB whereas what is picked up by the coax is not amped at all.
I have two of these and they've survived IL weather for over 3 years. 73
KAZ Barrington IL
On Thu, Oct 6, 2016 at 4:29 PM, Mark Pettifor <[email protected]>
wrote:
> For those of you who have DKAZ antennas, which preamp do you use? Do
> you
> find it makes much difference whether you put it at the antenna or in
> the
> shack?
>
> I need to "finish" construction on mine. Right now, I have two 470-ohm
> resistors alligator-clipped together for the null end, and a hand-wound
> transformer (my first ever) on a core made of unknown material, to go
> from
> 940 to 50 into a 50-ohm feedline.... RG-8X, 150 feet. That is also
> alligator-clipped together. It was for testing, ya know? :^)
>
> It's been pretty good as is, but I want to get it ready to survive the
> winter.
>
> BTW, it's amazing the amount of noise just a short length of RG-8X 100%
> shielded coax will pick up. I have it mostly on the ground, but have a
> small part of the run overhead for now (30 feet?) so I don't mow over
> it.
> Thanks!
>
> Mark Pettifor
> Near Goshen, INdx.com
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