Introduction

This page is just a collection of information and modifications for the 4/5BTV series of trap vertical antennas.

6 Blade and 3-Blade Spiders

There are two types of spiders, or capacitive hats, for the 4/5BTV. There is a 6-Blade Spider that attaches above the 20 Meter trap. Raising this spider raises the resonant frequency for 20 Meters. The other spider is 3-Blade Spider. It's only available on the 5BTV, but can be purchased separately. This spider attaches at the top of the 40 Meter section of pipe. It's intent is to add capacitance to the 40 Meter opertion so that tuning is easier.

If you don't have a 3-Blade Spider, it could possibly be made out of sheet copper or aluminum. Measuring from the bottom edge of the attachment ring to the end of the spreader the length is 7-5/8 inches (19.5 cm) long. Width of each strip 1/2 inches. Spacing, one at each half length point with one opposite the attachment screw inbetween the two half length points.

I imagine that if you wanted to add additional capacitance, and make that coil load better, you could snug up an extra cap hat element making a total of 4 spaced out in a circle. It might be worth an experiment.

Tuned Radials for Elevated Mounting

Band	Length
80M	67' (20.426 m)
60M	44' (13.41 m)
40M	33' (10.06 m)
30M	23' (7.01 m)
20M	16' (4.88 m)
15M	11' (3.35 m)
12M	9' (2.74 m)
10M	8' (2.44 m)

The 4/5BTV antenna work well ground mounted or elevated. When ground mounted, random length of wire are acceptible. Of course there should be as many as you can put in. I use a radial field with 16 - 30' lengths and can increase that to 32 - 30' lengths. But if you elevate the 4/5BTV you should have 2 to 4, 1/4 wavelength, tuned radials per band.

The table on the right lists the lengths needed for each band. The 15 Meter radial can be eliminated as the 40 Meter radial can work for both 40 Meters and 15 Meters.

I mounted my 5BTV at the top of a 18' section of 2" iron pipe. I constructed four groups of radials for 40, 20, 15, and 10 Meters. I didn't use 80 Meters so I didn't include a radial for that band. The radial groups were configured in a fan arrangement and kept the radials about 6" appart, using wood slats. I then attached them to the feed point and angled them down at about a 45° angle.

Multi-Band Ground Plane with Loaded Radials

In the May 1971 issue of Ham Radio, a short article suggested an arrangement of Inductive-Loaded radials, for a elevated vertical. This would not be very practical with a ground mounted vertical. While this was specifically used with a Hy-Gain 18AVQ, it should be able to be used by any of the trap verticals (e.g. 4/5BTV).

At the center of Fig. 1 (left) is the vertical antenna. The 18AVQ in this specific instance, but can be any shortened elevated vertical. The radials connect to the feed point ground. There are three single wire radials for 28 MHz (8'-4" | 2.51 m) and three loaded radials (overall 18.96' | 5.78 m). The 28 MHz radials are spaced a few inches away from the low-frequency radials.

Fig. 1 provides a good overview and Fig. 2 has the details for the loaded radials. If the radials are allowed to slope away from the antenna they can also be used a guys. With radials sloping away from the antenna at about 45°, the antenna provides a relatively good match to 50 Ω coaxial cable. The dimensions in Fig.1 are for the CW end of the band, but with a little cut and try, equal performance can be obtained on the phone bands.

The radials shown in the diagram, provide good performance on 3.5, 7, and 21 MHz. A separate set of radials are used for 10 Meters.

Add 80 and 160 Meters to a 4BTV or 5BTV

By adding some wire and two traps to the top of the 40 Meter section, 80 Meters and 160 Meters can be had using the 4BTV. First is a 6" jumper to a 40 Meter trap, followed by a 25' section to a 80/75 Meter trap. The final end, off of the 80/75 Meter trap is 45' in length.

The 80 Meter Resonator on a 5BTV is pretty narrow banded, so you can eliminate the 80 Meter Resonator and use the same method. It was easy for me. I have a 5BTV that uses the 80 Meter Resonator. However, it took a lightening strike and the Resonator exploded into thousands of tiny pieces. So now I have a 4BTV. You can use either purchased traps or make a coaxial cable traps. Coaxial cable traps should offer higher Qs and more isolation (higher impedance).

This may cause a bit of side stress making the antenna bend toward the 80/160 Meter extension. A rope guy in the opposite direction should counter the side stress.

Adding 12 and 17 Meters to the 4/5BTV

There are several version of this modification on the internet. Mostly they deal with the 17 Meter update. But overall, it the same modification. So I'm just presenting the overall idea.

Some of the versions tie the wires to the 6-blade spider, that is just above the 20 Meter trap. IMHO, that is a good way of breaking the spider. To me, the spider arms seem a bit brittle. Too much force could snap them off.

The drawing on the left is for the wire support. There are four required. The supports should be made from plexiglas or maybe fiberglass. They should be thick enough to resist bending, when the wires are tensioned. The center hole, 1-1/4", is sized to slip over the vertical pipe sections. The other holes are only big enough for the element wires to pass through. Starting from the bottom, one support is positioned at the base of the antenna. A second support is positioned at the bottom of the 10 Meter trap. The third support is positioned at the top of the 15 Meter trap and the forth at the bottom of the 20 Meter trap. You may need to use hose clamps, to hold the supports in place.

The alternate support drawing is just showing plastic pipe, lucite rod, or wooden dowel. If you are using plastic pipe, plastic electrical conduit should be used, for strength. While the dimension shows 1", it can probably be 3/4" or smaller. Just use what ever is on hand. 1/2" or 3/4" dowels would provide a lot of strength. To protect it from the elements, a good coating of shellac should be used.

To secure the pipe to the mast, you can use two interlocking hose clamps at right angles. One on the mast and one on the pipe/rod. This allows for easy positioning. The pipe/rod should then be secured just below the 20 Meter trap. Another method is to use two crossed tie-wraps that wrap around the mast, just above the 6-blade spider. And then, lightly securing the pipe/rod to the spider arms, for stability.

As an initial value, use 10' of wire for the 12 Meter section. Secure the wire to the feed point at the bottom of the U-Bracket mount. Then pass the wire through the bottom wire support and the support on the bottom of the 10 Meter trap. Finally, secure the wire to the wire support just above it, at the top of the 15 Meter trap.

For the 17 Meter section, start with 14' of wire. Like the other wire, secure the wire to the feed point at the bottom of the U-Bracket mount. Pass the wire through the bottom wire support and then through the two wire supports above it. Then secure the wire to the wire support at the bottom of the 20 Meter trap. Using the wire supports described, the wire sections should be spaced about 6" away from, and on either side of, the main section of the antenna.

17 Meters: 18.068 - 18.168 MHz - /4 = 12' 11-1/2" | 12.95833' | 155.5" (3.9497 M) - 12' 10-1/2" | 12.875' | 154.5" (3.9243 M)

12 Meters: 24.890 - 24.990 MHz - /4 = 9' 4-3/4" | 9.39583' | 112.75" (2.86385 M) - 9' 4-1/4" | 9.35417' | 112.25" (2.85115 m)

The formula for cutting the wire length is the old standby: 234 / Freqency (MHz) = length in feet. I used 13'-0" | 156.0" (3.9624m) for 17 meters, 9'-5" | 113.000" (2.8702m) for 12 meters

Possibly use the 102" (8'-6") CB whip for 12 and 17 Meters

This is one of my own ideas. I have a 102" CB whip hanging around. Even if you had to purchase these whips, they are pretty cheap. I intended to use the one I have on a mobile antenna setup, but thought it might be useful to enhance the coverage of a 4/5BTV. I made a measurement of the whip I had and came up with 103" (8'-7"), with Std 3/8"-24 Thread AS 1 Stud. The whip would make a nice strong add-on element. It would need some support at the top, to keep it from flopping over, but that should be pretty simple. One of the previously mentioned element supports could be used. However, even at 103", the whips are too short for either band.

So I calculated the lengths that would be needed.

17 Meters: 18.068 - 18.168 MHz - /4 = 12' 11-1/2" | 12.95833' | 155.5" (3.9497 M) - 12' 10-1/2" | 12.875' | 154.5" (3.9243 M)

12 Meters: 24.890 - 24.990 MHz - /4 = 9' 4-3/4" | 9.39583' | 112.75" (2.86385 M) - 9' 4-1/4" | 9.35417' | 112.25" (2.85115 m)

One of my thoughts was to add a small loading coil at the base of each whip. It looks like for 12 Meters (24.890 MHz) the whip would only require 112-3/4" - 103" = 9-3/4" of extra wire. That works out to a 0.515 µH loading coil. That's only 5 turns of wire on a section of 3/8" PVC (actual: 0-11/16" (0.66" | 17.1 mm)) form. However, if you are running your wire from the feed point on the 4/5BTV, you may need that much wire. So a loading coil may not be necessary. All you may need is a loose wound coil connecting the feed point to the base of the whip.

For 17 Meters (18.068 MHz), it would be a little different. The whip would only require 155-1/2" - 103" = 52-1/2" of extra wire. That works out to a 2.221 µH loading coil, which is 9 turns of wire on a section of 3/4" PVC (actual: 1-1/16" (1.05" | 26.7 mm)) form.

80 Meter Resonator Details

Everyone is interested in the contents of "black box" items. Or just items that you just can't see into. You kind of know what's in there, but no specificsl. However, most of us are usually not willing to take it apart and risk ruining it. Well, while I was putting up my 5BTV, it got a little out of control and the 80 Meter Resonator come down on a section of fence made out of iron pipe. This caused the internal coil form to crack. I had to take it apart to fix it, so this gave me a chance to look inside the 80 Meter Resonator. So this is just a compilation of details that I gathered during that fix.

Note that, while the initial repair was successful, it was all for naught. A few years later, when the 5BTV was mounted at the top of a 18' section of iron pipe, it was the subject of a lightening strike. Now, except for the two end caps, there is nothing left of the resonator. It was literally "blown to smithereens". All that is left are little tiny shards of bakelite and wire, spread around a 100' radius.

• Coil Form - The coil form is made out of Bakalite and is groved for the coil wire. The groves are not very deep (.008" - .009") but are enough to keep the wire from moving around. The groving than makes the inside diameter of the Coil 1.98". The outside diameter of the coil measures 2.111".
• Wire - The wire appears to be a silk covered Litz wire. The overall wire diameter measures 0.071" and is close wound for 14 turns per inch. Each strand measures 0.0015" in diameter, which is about a AWG #46. At 0.071" the wire is roughly the size of a AWG #16 wire. According to a Litz wire chart, a Litz wire 0.071" in diameter, with AWG #46 (0.0015") strands, should contain about 1050 strands and be 2.593 kcmil (kcmil = Thousands of Circular Mils). This is then equivalent to a AWG #16 wire. This takes into account the thickness of the overall covering.
• Number of Turns - I counted the coil turns and came up with 116. At 14 turns per inch, this makes the coil to be ~8.28" long. I measured the coil to be 8-1/2" long, which then sounds correct.
• Final specifications - 116 Turns of AWG #16 Litz wire close wound on a 1.980" diameter Bakalite form. Length is approximatly 8.28".
• Rebuild - I am going to rebuild it using a PVC pipe that is 2" OD. Since I don't have Litz wire, and really don't want to buy any, I will make my own Litz wire using an enameled wire that measures 0.0185" (AWG #27.4) diameter. It should take 14 strands to get a AWG #16 or 2.551 kcmil (kcmil = Thousands of Circular Mils). The coil will be 116 turns, at 14 TPI, which will then be 8-5/8" (219.379 mm) long. An approximation of the inductance is 148 uH. At 62' 3-1/4" per strand, and 14 strands, this should be about 871' 9-3/8" of wire to make the new coil. I may try to use 0.060 plastic Weed Eater string to keep the turns spaced evenly and prevent them from moving.