[Lowfer] Summer antenna project underway (a long ramble).

[Philip Atchley]

Hi,

I've been away from this list for quite some time (though I've continued 
chasing NDB's).  Yes, my primary interest is NDB's rather than "Lowfers", but 
I hope I won't be ostracized from the group for that failing ;-).  This list 
was VERY helpful to me when I first started chasing beacons.

I read the ARRL note about the possible Amateur activity around 500kc and if 
it comes to pass, sounds like something that will be very interesting to 
"listen for".

Now to the main reason for the post (kind of a long ramble).

**********************************************************

The summer antenna season is upon us, and I have that familiar old "itch" 
<grin>. Of course, some folks wait until mid January/February before doing 
those needed antenna chores.

Anyway, in anticipation of a GREAT (!!) Winter 05-06 LF listening season, my 
summer projects include updating and adding to, my LF antenna farm. Living in 
a mobile home with a side yard (garden) that is only about 2 meters wide by 
perhaps 22 meters long, and a back yard that is roughly 1 1/2 meters deep by 8 
meters wide, there is NO place to put up something like the usual K9AY etc. 
All antennas here are mounted OVER the sheetmetal roof and sheetmetal side 
awnings of the mobile home. Actually, this is an advantage as it provides some 
shielding from Noise fields inside the mobile home.

Here is a list of some different antenna configurations that I've used over 
the past 5 years and how they worked. ALL except the crossed loops were 
mounted above the roof of my mobile home.

1. 20 meter long coil loaded sloper (Alpha Delta DX-B designed for 160, 80, 40 
& 30 Meters). Used for the past 5 years WITH a tunable low noise pre-amp. 
While NOT designed for LF, this antenna has been a good performer and my 
PRIMARY antenna. It's STILL in use. I've built a number of different tunable 
pre-amps and Low pass filters for use with it (most used the venerable MPF-109 
and 2N3904). The latest pre-amp uses a much improved design combined with my 
homebrewed multicoupler.

2. 2 meter diameter crossed, tuned loops, built on a PVC frame. The two loops 
were at right angles to each other and contained several hundred feet of 12 ga 
wire. It sat on the ground with the bottom section of the coils raised on legs 
to about 3 feet above ground level. A VERY large contraption for this QTH! The 
selected loop was switched via relay to a varactor tuned preamp (MPF-102 and 
3N3904) at the base and was then routed to the shack. VERY SENSITIVE, but 
since the ONLY suitable location was directly above the underground power 
lines behind the mobile home (bad move), it picked up a HUGE amount of QRM/QRN 
from the same power lines. The concept proved the viability of the antenna, 
but I SCRAPPED IT after 1 season's use because of it's location (and I 
couldn't even give it away because of problems in transporting it). NOTE: If 
anyone ever decides to build one of these, I suggest a PVC pipe LARGER than 
the 1 3/8" schedule 40 pipe that I used. With that much 12 gauge wire hanging 
on it, it required a LOT of cross bracing to keep it from bowing.

3. Active whip using a MPF-102 and 2N3904 transistors. It seemed to be quite 
sensitive and heard quite a few beacons, a few NOT heard on the sloper. When I 
FIRST installed it I didn't have any trouble with IMD from the broadcast band. 
HOWEVER, it later developed severe IMD problems and I'm not sure if the unit 
got "static zapped" or whether something changed in the configuration/power of 
the local BCB stations. I suspect the latter as they seem to be always 
changing "something", callsign pattern etc (they seem to be a lot stronger 
than they used to be). It was scrapped after about 1 winter season.

4. Tuned FERRITE BAR antenna. This was another one of my strange contraptions. 
It consisted of TWO ferrite bar antennas, mounted one above the other like an 
"H" on it's side (separated by about 12 inches). One was for the LF beacon 
band, the other for the standard broadcast band. The desired "rod" was 
selected via relay and applied to a varactor tuned pre-amp. NOT as sensitive 
as the sloper/pre-amp combination, the ability to rotate it and null QRM 
allowed me to hear quite a number of beacons NOT heard on the sloper. Looking 
back, it REALLY should have had MORE ferrite material in the LF loopstick. 
This was probably the BEST PERFORMING 'COMPACT' antenna I built, if only 
because it allowed nulling of QRM and even the nulling of powerline noise 
often helped significantly.

5. Large roof mounted rotatable loops (1 meter or greater in diameter) have 
NOT been used here due to the problems associated with trying to keep them up 
in the air and rotating them. Because all of the mobile homes in the park are 
about the same height and provide an effective "windbreak", we get some pretty 
strong winds across the top of this mobile home!

OK, now that the preliminaries are over, let's get back to the main reason for 
this post, THE DREADED SUMMER PROJECT 8^) Actually, I should say projects as 
there are a couple in the planning stage.

Looking back over the performance of the various antennas that I've built, I 
intend to build two of them. ANOTHER rotatable Ferrite Loopstick antenna AND a 
"Roelof Mini Whip", POSSIBLY in the same housing to Optimize "Antenna Mast 
Space", use a single coax run and instant switching between antennas. I figure 
that by using a PVC 4 way coupler, the "miniwhip" should be able to project 
ABOVE the loopstick and a mini-relay used to switch between the two units.

HOWEVER, the overall length and cross sectional area of the FERRITE material 
will be greatly increased over the last loopstick experiment. This being done 
by gluing multiple ferrite bars end to end and having several laid parallel to 
each other, with the coil wound around them all. So, once the project gets 
underway I'll be putting out "wants" for suitable ferrite bars on several of 
the mail lists I belong to. I already have 4 of them, an 8 inch and 4 inch one 
that are identical in diameter and shape (flatted on one side), and two 5 1/2 
inch units that are 'slightly' slimmer. My rods probably aren't the BEST 
possible choice as they are actually BCB units salvaged from old radios. But 
they're what's available to me.

While I realize that it would be BEST if all the ferrite rods were the same 
type/manufacturer, due to budget constraints, THIS CAN'T BE DONE. Have you 
seen the price Amidon etc gets for NEW ferrite bars? It's outrageous! I'll 
just have to work with what I can get and wind whatever number of turns it 
takes to get resonance.

I thought that I'd clean them of ALL wax residue, carefully smooth the ends, 
glue them together, putting very thin Teflon tubing along "hollows" created by 
the round rods for "some" strength, then coat the entire thing with Beeswax 
(to easily hold coil turns)or similar before winding the coil. I thought I'd 
try to get some Litz wire for the coil (if I can't salvage enough from the 
loopsticks).

QUESTION: Has anyone on this list (besides me) built one of these ferrite loop 
antennas using multiple rods before? Did you glue them together using 
superglue, or?

YOUR THOUGHTS AND SUGGESTIONS ON THIS SUBJECT?

73 de Phil,  KO6BB
991 Different NDB's heard to date.
MY SWL QSL GALLERY: http://photobucket.com/albums/y123/KO6BB/
MY WEB PAGE:    http://www.geocities.com/ko6bb/
Merced, Central California, 37.3N  120.48W  CM97sh