A Saga by Linus  

Click Here To Read Version 1.0

Hello again, Loop Lovers!

It's 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.

Plus, decent pictures were tough to acquire, but now I have a few of those as well.
I've been receiving a number of mails asking if or when I would ever update this project, and now that I have been able to get SOME kind of work done, I am happy to be able to add a few ideas and show a few things.

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.

Click On Any Image To Enlarge

You can see how simple the set up is, but lightweight and durable.

I DID 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.

Now To The Updates
First, I decided to make the remote/varactor tuning system I mentioned in the original article. This would seemingly remove the need for any meaningful counterweight, since I was removing the weight that the air-variable cap and ferrite rod were imposing.
In the place of the cap/rod arrangement, there is now the varactor diode circuit, which weighs a little more than *nothing*.

It is an RCA jack connected from its (+) pin to an MVAM109 diode, which is in series with another MVAM109 diode, then wired to one of the ends of winding originally connected to the old variable cap.

The (-) or ground of the RCA jack goes straight to the other end of winding which had been originally affixed to the cap.

As you 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.
You'll see how the RCA jack on the loop comes into play in a moment.

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.

The image of the inside of the box shows you how forgiving and simple it can be to just wire it hard and let 'er rip.

I have 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.
This circuit can be operated for many hours on a 9v battery, but I thought I'd like it to be powered from 12v, from the power supply I use at my post. So instead of a 9v clip and holder (which you can CERTAINLY use if you wish) I added a DC plug and wired it appropriately. Easy.

Also, 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.

The component list, such as it is:
R1, 10k potentiometer
R2, @47k  or so, not crucial but close would be good.
C1, 0.1mH ceramic, which prevents the DC tuning voltage from being shorted by the receiver's input circuitry.
9V Battery clip and holder
(Optional, 12v DC jack)
(Optional LED and matching resistor)
(Optional power switch, SPST)
Two (2) RCA female jacks
Project Box, knob, lettering stencils if you wish.

The 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.

I used 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.

A few notes:
Make sure that you wire your MVAMs to be in series just as you would for LEDs, since they can get very fussy about polarity.

I know 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.

So, does it work? Yes indeedy.

As well as the passive tuning/pick-up system, indeedy.

It is easier to tune without upsetting any balance because I've removed the cap from the Loop itself.

Plus, 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 notice my nulls are about as deep as they were with the cap/ferrite system, and the balance is not altered in any meaningful way by changing the tuning method.
More playtime is needed to really see if I've done anything detrimental to the original set up, but it seems like a success.

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.

I am noticing that the directionality of the loop is a little dulled IF I use poorly matched coax or too long a run from the loop to the box OR from the box to my receiver.
I shortened the Antenna coax run to three feet, still enough to get full turning/tilting, and used newer Belden (better) cable from the box to my receiver. This brought everything back to 'spec' as I had been used to. More trial is needed though.

I also 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.

Linus, The GrtPmpkin


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