Hi Guys
Tks for the messages and for the interest in this neat antenna.
Here is how to build the BC "Trapper" traps (and how to tune the BC
Trapper/Wire Version of the BC Special Loaner Antenna).
Parts List
1) 18 Feet RG 213 (poly dielectric) 50 ohm coax
2) About 2 feet of schedule 40, 4" diameter PVC septic line (Schedule 40 is
relatively thin wall and lighter in weight than schedule 80 pipe) + four (4)
end-caps for 4" diameter PVC
3) 4 feet of #12 THHN stranded copper wire
4) 4 Rolls of PVC Electrical Tape
5) One tube of GE silicon sealant - the "Home Line"
6) Four (4) 1/4" eyehooks, (8) 1/4" flat washers, (4) 1/4" nuts, (4) 1/4"
lockwashers
7) A small can of PVC pipe cement
Trap Assembly
1) Prepare two lengths of RG213 as follows: Cut two lengths, one to 11 feet
0 inches and the other for 6' 3.5". Separate the braid from the poly center
dielectric in order to create "pigtails" 2.75" long at each of the four ends
of coax. The 11 foot length will be used for the 80M trap and the 6' 3.5"
length will be used for the 40M trap.
2) Place a PVC end cap TEMPORARILY on the end of the 4" PVC
3) Size the actual length of PVC pipe required by temporarily winding the 11
foot length of RG213 around the 4" PVC. In order to wind up with smallest
required amount of PVC, start the coil about 1/2 inch below the point on the
PVC where the end cap ends.
The RG213 should be TIGHTLY wound with each turn directly adjacent to the
preceding turn. It may be necessary to tape the first several turns
temporarily to the PVC in order to effect this - esp on the 80M coil.
When all turns have been wound, estimate the additional length of PVC
required to accomodate the lower PVC end cap. Now remove the RG213 and cut
the PVC pipe to final length.
With one end cap still in place, drill a hole in the PVC at the point at
which you started winding the coil. This hole should be just large enough to
ram the pigtail through and, ideally, should be as snug a fit as possible on
the black outer jacket of the RG213 when completed.
When the hole size is right, stick one end of the coax pigtail into the PVC
(from the outside of the coil) such that all of the 2.75" of coax pigtail
winds up inside the PVC plus about 3/4" of black coax outer jacket.
Now wind the coil, tightly wrapped, and use electrical tape to hold the turns
in place as you go, if required.
When you are nearing the bottom of the coil, you will need to estimate where
to drill the lower hole for the coax to enter the center of the PVC.
BE SURE to allow sufficient length of the lower coil coax to enter the PVC
center SUCH THAT THE PIGTAILS CAN REACH EACH OTHER INSIDE THE COIL! This is
necessary in order to make the internal connections required for the coaxial
capacitor inside the PVC pipe. If the lower pigtail needs to be increased
in length to achieve this, separate a wee bit more braid from the poly, if
required.
When you are sure you have estimated it correctly, drill your lower hole,
insert the lower piece of the coax into the PVC and test the pigtail lengths
to ensure they will actually reach each other comfortably - inside the PVC.
Now tape your lower turns snugly to the PVC - in order to hold them in place
while you make your connections.
Making Your Connections
To form the coaxial capacitor inside the coil, connect the braid from one
pigtail to the center conductor of the other pigtail. Do NOT connect braid
to braid or center conductor to center conductor!
Initially, this connection should not be soldered to allow for GRID DIP meter
testing of the trap's resonant frequency, if desired. I have found that
these dimensions resonate anywhere from between 3490 - 3525 typically.
Should they resonate significantly LOWER, then the coax can be trimmed and a
new hole drilled for the lower coil pigtail entry. If they wind up short -
OOPS! Time for a new piece of coax.
However, I have made up about 7 of these and 11 feet with just enough pigtail
leads to reach inside the coil is just about perfect for 3500-3525 on 80M CW.
When you are happy with the trap's resonant frequency, twist these wires
together well and solder this connection liberally! Do you very best to take
up as much tension as possible between the lower and upper pigtails as you do
this. In other words, do not leave alot of slack inside the coil/PVC. If
you get it just right, there will actually be some holding tension inside the
PVC on the outer coil windings themselves.
This leaves you with two leftover ends of the pigtails - one braid and one
center conductor. One should be angled toward one end of the PVC - the other
toward the opposite end of the PVC.
To each of these, the braid and the center conductor, a 12" piece of #12 THHN
stranded wire should now be soldered. Again, twist these wires together well
- and solder them liberally as they will never be accessible once you close
up the PVC - and they will be handling 1.5KW up in the air!
>From the inside of the PVC, liberally seal the holes where the coax enters
the PVC using GE silicone glue/sealant. It's also a good idea to goop up the
soldered connections inside the PVC as well to ensure they don't float around
inside somehow - although proper tension on these leads will not allow this
to occur.
Preparing the Endcaps
Drill a hole in the center of each endcap just large enough for the 1/4"
eyehooks to fit through. Mount the eyehooks to the endcaps using one
flatwasher on the inside and one flatwasher on the outside of the endcap.
Tighten the eyehook in place using the 1/4" nut inside the coil. Get this
tight inside and use a lockwasher if in doubt! These eyehooks are going to
hold up the weight of the traps AND the weight of the wire as well, so they
need to be tightly affixed inside the PVC tube. They too will be inaccesible
later!
Now drill a hole somewhere in the PVC endcap just large enough for the THHN
#12 wire to SNUGLY pass through.
When both PVC endcaps have been so prepared, it's time to glue them onto the
PVC. This requires some dexterity, as you must first pass the open end of
the #12 wire through the hole in the endcap and spread PVC cement on the
inside of the end cap and onto the top of the PVC as well - all at the same
time.
Since PVC cement dries in seconds, this needs to be done quickly. Push the
PVC endcap onto the PVC as far as it will go and pull the #12 THHN lead snug
as you do this. You should end up with about 8" of THHN wire outside the
coil when completed.
Finishing Off the Trap
You should end up with a tightly wound coaxial coil around the PVC and the GE
lubricant should keep water out of the coil. However, to be doubly sure, I
now tape the entire outer surface of the PVC with PVC electrical tape -
tightly wrapped. Usually I expend 1-2 rolls of tape PER TRAP to keep the
coil turns snug and to keep water from ever seeping into the PVC center.
(You do NOT want a swimming pool created inside the PVC - ever!)
I also seal the endcaps liberally around the eyehook flatwasher and around
the eyehook as it exits the endcap. Also seal liberally the point where the
#12 THHN wire exits the PVC tube through the endcap. This I do several
times - at about 6 hour intervals to allow the GE silicone sealer to "set up"
properly between each coating.
Now your trap is completed.
The 40M trap should be constructed exactly the same way - but using the 6'
3.5" piece of RG213. This coaxial length should yield a resonant 40M trap
around 7.000Mhz, plus or minus. Again, trim to final length with a grid dip
meter, as necessary.
Assembling a BC Trapper
The three dimensions of #12 THHN or #10 THHN wire required are as follows:
Ground Level to 40M trap - 33 feet (cut to 35 feet initially!)
40M trap to 80M trap - 26 feet (cut to 28 feet initially!)
80M trap to end insulator - 41 feet (cut to 44 feet initially)
The various sections of wire should be tied and knotted around the 1/4"
eyehooks on the ends of the traps. Allow enough wire on the dead ends to
connect to the pigtail lead of #12 THHN exiting the PVC endcaps for making
your connections.
Initially DO NOT SOLDER these connections - just twist them well!
Hang your trapper - and BE SURE to pull the tail of the "L" out into its
approximate final position when doing all tuning/testing/trimming. If you
let it dangle, you will be sorry later as it makes a real difference in the
final tuning of the 160M section of the L!
Start with 40M and trim the 33 foot section to final length on 7.0.
Next tune 80M by trimming the 26 foot section to final length on 3.500.
Now move to 160M and trim the far end of the tail to final length on 1830 (or
your preferred QRG of operation).
Now go back and RECHECK 40/80/160.
When you do this - again, BE SURE to hang your "tail" of the L in its final
elevated position out to its far support.
When you are happy with the results (I've not seen 40, once set being
impacted by 80, nor have I seen 80M being impacted by 160M, but it's best to
CHECK FIRST anyway to be sure!) Then it is time to solder all connections
and tape up these points liberally with PVC tape.
What you wind up with is a final length of around 100-102 feet for a BC
trapper.
The antenna works as a full sized 1/4 wave vertical on 40M, as a loaded 1/4
wave vertical for 80M (if all 60 feet of it are vertical) and as a loaded 1/4
wave inverted L on 160M.
SWR readings should be excellent at 1830/7.0/3.5 and a tuner will be required
for 40SSB and 75 Phone.
(I suppose the traps could be cut for SSB, but my experience has always been
that it is BETTER to employ a longer antenna with a tuner on 40SSB and 75SSB
- rather than to try to use a tuner on CW for an antenna and traps cut for
SSB. Aren't MOST 160M guys CW hounds anyway - with SSB merely an
afterthought?)
How does it work?
Really well actually! It was remarkable how well this thing worked at
various locations where I have seen it used.
I think 5X4F once used this antenna at 5Z4FO - (K8GG could confirm this
though!)
Hope the construction details are clear.
Good luck to those who inquired and many thanks to K8GG, W0CD and W8UVZ who
designed it in the first place!
It is a fine little antenna - three bands for the price of one radial system!
If you decide to try one, pse let me know how it works for you at your QTH.
73 Jeff
K1ZM@aol.com
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