[Lowfer] FWD: Antenna design idea question

Wed Sep 30 03:14:56 EDT 2009

Hi Mary and Bill,

Thanks for your response and input.  After a lot of reading and 
responses on here I believe that I see the shortcoming of this design.
# As the antenna has more capacitive toploading the importance (and thus 
the gain) of the distributed inductance decreases.

Alan,G3NYK, response is very interesting and lead me to some very 
interesting reading.  It appears that running the windings the whole 
length we are wasting a lot of power into near by trees and structures. 
Toni,.HB9ASB, used this design and had very good reports but there isn't 
much info on how he built his antenna. ON7YD's web page has some info 
that's very interesting.  With this design you don't want to use a 
capacitor hat because as the antenna has more capacitive toploading the 
importance (and thus the gain) of the distributed inductance decreases 
and as the capacitance of the vertical part of a helical antenna is 
rather large compared to a 'straight' vertical (because of the larger 
diameter of the vertical part) the effect (and thus the gain) of the 
capacitive toploading decreases.

I believe that using a combination of Finbar O'Connor's (EI0CF) design 
for a Spiral toploaded antenna with Spiral helical windings below it 
that the efficiency of the radiator will be improved.  I will only use 
the upper area of the vertical for the helical windings and go with no 
capacitor hat first but will add it if needed later.

73,
Mike
K1EG

# As the capacitance of the vertical part of a helical antenna is rather 
large compared to a 'straight' vertical (because of the larger diameter 
of the vertical part) the effect (and thus the gain) of the capacitive 
toploading decreases.

# As the antenna has more capacitive toploading the importance (and thus 
the gain) of the distributed inductance decreases.

Mary & Bill wrote:
> Hi Mike,
>
> About 15 (or 20) years ago I got excited about getting on the lowfer 
> band and built an antenna similar to what you have in mind.
>
> I wound turns on 4 inch PVC sewer pipe.  I spaced the turns by winding 
> a string (about the same diameter as the wire) along with the magnet 
> wire.  The string was later removed and the whole thing shellacked.
>
> I had only three sections of pipe because of how unwieldy even thirty 
> feet became.  The sections were strapped together using #12 sheet 
> metal screws at the joints.
>
> The design came from several antenna books and were based on long, 
> skinny, helical design as have been used on mobile rigs for years.
>
> I had a three foot disk of sheet aluminum at the top and about 8, ten 
> foot ground rods scattered about the yard (in addition to the metal 
> water pipes in our home).
>
> I was using an HP audio generator as a vfo and a 6AQ5 with the final 
> tank coil wound on an oatmeal box.  It seems to me that I had to add a 
> small (few turns on six in diameter form) coil at the between the 
> bottom of the antenna and the center of the coax in order to bring the 
> whole thing into resonance.  I was successful at link coupling the 
> transmitter (in the house) to the antenna (in the side yard).  The 
> whole system loaded up beautifully and with a long pole (and a ladder) 
> I could light a florescent tube at least two or three feet away from 
> the top of the antenna.  I was running about 200 volts on the final 
> and initially had it adjusted it for about 1 watt input.  Later 
> throwing caution to the wind (and after having zero success at hearing 
> the station at more than three blocks away from home )  I threw 
> caution to the wind and ran a whole five watts  to the final.  The 
> florescent light was brighter but I still seemed to be limited to less 
> than three blocks of range.  I was using a Realistic DX100 for a 
> receiver at that time and I now suspect that the problem was in the 
> abject lack of sensitivity of that receiver below the broadcast band.
>
> You should have seen us.  I made a second antenna by wrapping two, ten 
> foot, three inch diameter PVC pipes with close spaced wire and mounted 
> this antenna on my kids wagon, along with a car battery and the 
> receiver.  The antenna was guyed to outriggers fitted to the wagon.  
> My wife (Mary/WB5DVA) was running up and down the street using a 
> 2meter HT to send back signal strength reports while I keyed the 
> transmitter (later tests were made using a drum keyer) fashioned from 
> an old relay and a can with bolts sticking out of it).
>
> Interestingly, in one direction she could easily go five or six blocks 
> and still have a good signal, but if she turned up a side street the 
> signal was gone withing 25 feet from the intersection.  We found that 
> we could map out the city water pipes extremely well with this rig.
>
> Mary and I have built lots of HF antennas of nearly every type (except 
> a cubical quad).  I have spent many an evening pondering why we had 
> such poor luck with our lowfer antenna.   The conclusion that I have 
> come up with makes no sense at all, but it would seem that we were 
> generating a huge electric field and almost no magnetic field.  If it 
> takes both to propagate a radio wave, that might be the reason for the 
> fast drop off of a signal from an antenna that for all purposes seemed 
> to load and work perfectly.
>
> We nade a grid dip meter that was tuned with a bunch of ferrite from 
> old portable AM radios that were glued together and run in and out of 
> the rather large coil.  Using a receiver for calibriation, it worked 
> pretty well in tuning up the antenna before it was mounted in place. .
>
> I will be interested in your results.
>
> I have also seen the information about using the same length of wire 
> that would normally be used for an open antenna at that frequency, but 
> I suggest that the distributed capacitance, etc. makes this only a 
> starting point at determining the amount of wire used.   If memory 
> does not fail me,  I believe that the length of wire that we used was 
> somewhat less than the length of an open wire antenna.
>
> I still have two sections of this antenna in a storage locker.  I used 
> the wire on the third for another project.   Some day I may pull them 
> out and do some more tinkering with them.  Until that time this whole 
> project is shrouded in mystery and frustration.
>
> Bill/W5TJI
>
> PS Thanks to Paul for forwarding your interesting message to me.
>