[Lowfer] Antenna Questions

Bill Ashlock ashlockw at hotmail.com
Wed Mar 4 15:49:52 EST 2009


"All-in-all, the Part 15 stuff has set back the development of amateur
LF in this country"

 

Warren, you really know how to hurt a guy. And one that has been pivotal in your establishment a strong reputation in Part 5 loop transmitting. Also I wonder what Lyle Kohler and other Part 15 pioneers would feel about your comment? In my case check out just about any antenna text book written over the last 100 years and it will state that transmitting loop antennas at low frequency have no practical use. 

 

Bill Ashlock
 
> Date: Wed, 4 Mar 2009 12:21:29 -0500
> From: wd2xgj at gmail.com
> To: lowfer at mailman.qth.net
> Subject: Re: [Lowfer] Antenna Questions
> 
> Jim,
> 
> Without a doubt go for a Part 5 license!!!
> A lot (but not all) of the miracle reports from "Part 15" beacons are
> from beacons that are stretching the definition of Part 15.
> For example, there is a guy in CT who runs 4-5 watts out (maybe more)
> on 512kHz into who knows what kind of antenna (certainly not 3m long -
> the legal limit!) There are also people who stretch the definition of
> a "15 meter" antenna into a 200' circumference loop, the rationale
> being that it would fit into a 15mx15m cylinder - I believe the FCC
> was asked for clarification and there response was that the antenna
> should have a total conductor length of 15m! (not 60m). The rules
> also force you into doing dumb things like placing your transmitter at
> the antenna feedpoint rather than in the hamshack where it belongs.
> 
> The losses are so great and the noise levels are so high that you
> need all the power you can muster, especially if you want to do
> something more than just beacon all the time. (Piss-weaker's 1st Law -
> the weaker they are, the longer they talk!) I believe it was Mike
> Dennison G3XDV who said that "if you haven't had a fire you're not a
> real LF experimenter" If you go the one watt DC input
> 15m antenna route the best you can hope for are beacon reports while
> running QRSS (or possibly WOLF) - the data rate will be too slow for
> a real-time QSO unless you live within a short distance of another
> experimenter. You will need to run some real soup to make QSOs over
> any distance reliably.
> 
> All-in-all, the Part 15 stuff has set back the development of amateur
> LF in this country, and I can prove it.
> If you look at the amount of activity generated in the U.K. in the
> first few years after they were granted a 2200m ham band by any
> measure, (number of active stations, number of contacts, number of
> new circuits and innovations) it far exceeds everything done in
> the US after decades of decades of Part 15 experimentation. Ideally
> we should have LF/MF ham bands since the Part 5 process is
> slow and cumbersome, and relatively few people make the effort to
> get a Part 5.
> 
> 
> -- 
> 73 Warren K2ORS
> WD2XGJ
> WD2XSH/23
> WE2XEB/2
> WE2XGR/1
> 
> 
> On Tue, Mar 3, 2009 at 7:49 PM, Jim <w4jbm at bellsouth.net> wrote:
> > I'm hoping to have a LowFER beacon on from West Georgia in a couple of weeks.
> > Actually had hoped it would be on by now, but a bout with the flu and a lot
> > of travel with a new job has interfered with the fun.
> >
> > I'm thinking of building both a vertical and a loop antenna just so I can
> > tinker with both styles. We have 20 acres and there are parts that are
> > heavily wooded. Also the portion near the house is not the highest part of
> > the property (but not down in a hole either).
> >
> > My shack is in the basement and about 50 feet to the side is a fairly good
> > sized (probably 50 x 50) pen where we keep the dogs when we don't want them
> > running the ranch. It is constructed with t-posts and welded wire.
> >
> > There are a few short trees to the back of the pen, but basically I've got
> > tall trees on both sides of the pen with a clear shot across. The trees are
> > pines and they sway heavily in the wind.
> >
> > For the vertical, what I'm thinking is running about 30 feet up and then
> > having a T at the top with maybe 20 feet on each side. (Staying within the 15
> > meter total, just throwing out rough numbers. But also using what I guess
> > some consider a liberal interpretation that you measure the radius at the
> > top, not the diameter.)
> >
> > One question I have is, does it really matter if the 30 feet are "vertical",
> > or could they slope and still have the T for top loading? I'm thinking I'd be
> > ahead to slope towards the corner of the dog pen so I can use the fence wire
> > as the ground instead of having it all drop down in the middle of the pen.
> >
> > Also, is there value in having a loading coil up where the T is formed in
> > addition to the coil used for matching at the bottom? I was going to build
> > the insulator of the T out of something like 4" PVC and wind a foot or so of
> > coil on it in addition to using it for mechanical strength.
> >
> > One the loop, there are a pair of trees about 40 feet apart and probably 60
> > feet tall or so on one side of the dog pen. I'd like something easy to
> > install and work on and I've had my share of frustration with slingshots,
> > bows and such. So what I was thinking was getting around 50 feet of PVC pipe
> > to put at each end. Basically I'd hook the side of the loop to the PVC pipe
> > and then strap the pipe to the tree. I was going to try to get the bottom of
> > the loop about 10 feet off the ground.
> >
> > If I went that route, would there be any advantage to having what amounted to
> > loading coils in the side of a loop? I could either have a gentle wrap (a
> > turn a foot or so) up the entire length or I could put in more
> > traditional "coils" bottom, middle, and/or top. I was thinking of using 2"
> > PVC (because I've got some handy) with a gentle loop up the entire length. I
> > have no particular reason for going that route, it just somehow strikes me as
> > an interesting thing to try.
> >
> > I've also thought that I might use two or three conductors up the PVC in
> > parallel to reduce the resistance in that portion of the loop.
> >
> > At this point, I'm just kind of tinkering. I figure I'll try a couple of
> > different things that are fairly "low effort" and then put more effort into
> > the approach that seems to get the best results.
> >
> > I have got most of the hardware built. The only thing I need to do is build
> > a "driver" circuit that will take the output from the crystal oscillator out
> > over some coax to the final which will be at the antenna location. Right now
> > I can drive the final with three or four feet of coax, but need something
> > with more umph to drive 30 or 40 feet of coax. Keyer is a PICBeacon with 5
> > wpm, QRSS-10, QRSS-30, or QRSS-60 being selectable.
> >
> > Any antenna suggestions would be welcome. And like I said, looking more to
> > tinker instead of for the definitive "this is the best" right now. With all
> > the trees, I'm thinking the loop may be where I end up, but who knows. After
> > all, that's how we justify going for Part 5 licenses from the FCC at a later
> > point, isn't it? :-)
> >
> > 73 de
> > Jim W4JBM
> >
> > http://www.geocities.com/w4jbm
> >
> > "With a soldering iron in one hand, a schematic in the
> > other, and a puzzled look on his face..."
> >
> > Working the world from the New Dog Iron Ranch!
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