again, Loop Lovers!
the Ol' GP himself, Linus, here to offer an update to my original
Wooden Alt/Az Hoop Loop project, after a few years of LOTS of other
things I needed to do. Some of my hobbies got put on the backburner,
as they say, and it's taken me some time to get back around to re-evaluating
some of my favorite projects.
decent pictures were tough to acquire, but now I have a few of those
First, here are some pictures of the loop as first built.
One is a full view, another is a close-up of the air-variable cap and ferrite arrangement on the base of the Inner Loop.
see how simple the set up is, but lightweight and durable.
have to wrap some gaff tape around the windings to allow some smoother
turning/tilting of the loop, as the windings slackened a bit after
a month or so. The solution was to undo the connections to the variable
cap, retighten the windings, and reset the connections to the cap,
and THEN cover the thing with gaff tape. (I'm sure there are more
eye-pleasing methods of covering the windings but I am not too concerned
about it. I think it looks rather sleek, anyway!)
No slacking since then, I can assure you.
To The Updates
can see, the diodes are housed in a little plastic box I found in
a junk drawer, just for safety and dust issues. The box glues/double-sided
tapes to the Inner Loop easily.
Now for the power and control box for this tuning system.
I have supplied a simple schematic for the varactor control circuit, and it does not have to be built on perfboard or anything so fancy.
added a few things into my control box for my own edification, but
a look at the wiring image and the schematic will show you where to
add these features if you wish.
since I wanted to be sure it was ON or OFF (I tend to forget and
leave things powered up for hours at a time), I added a small LED/resistor
inline with the power jack, and a SPST switch to run the whole shebang.
best way I can explain how it works is that the voltage is applied
through R1, and as R1 is varied, the voltage is varied and output
to R2, and then on to the varactors onboard the Loop, which tune up
or down depending on voltage supplied.
The signal is returned (bypassing any receiver shorting via C3) to the control box and out to your receiver input.
RG174 fitted with RCA plugs to connect the control box to the Loop.
About four feet is the most I can use before I notice any imbalances
in the system, or any distorting of signal, pattern, etc.
The 'Receiver' out RCA on the box goes to my receiver via a three foot run of RG59 coax, properly fitted with an RCA plug and a PL259, respectively.
there may be some confusion about using two MVAMs when one ought to
do fine over the MW range.
Well, I *think* that using a cable longer than a foot or so to get from the box to the Loop might be skewing things enough that two MVAMs will do better in allowing full MW coverage. At any rate, two MVAMs in series works over the whole range where one will not (unless I use a short stub of coax which kills the whole idea). More experimentation will solve this.
it work? Yes indeedy.
as the passive tuning/pick-up system, indeedy.
easier to tune without upsetting any balance because I've removed
the cap from the Loop itself.
there IS that dangling coax from the varactor box to the control box,
but this is no more intrusive or annoying than the original design's
ferrite-cable to the receiver.
I have noticed that the counterweight I first assumed would be unnecessary is still needed, though it is MUCH smaller than the one needed with the cap/rod set-up.
changed the nylon swivel bolts to metal, temporarily, because one
of the nylon bolts broke after a lot of service, and I had no replacement
handy. Oddly, the metal bolts offer better mechanical stability WITHOUT
any noticable skewing of patterns or signal, etc. I expected things
to be messed up at least a little bit by using metal instead of nylon,
but so far...?
I hope this has helped anyone and answered a few more questions. If not, feel free to write me.
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