Properties of Hustler Whips used as dipoles

 
 As I do not have space to erect a large antenna, I decided to see what could be done to make a simple dipole that was self supporting and rotatable. My first experiments with this involve making only mono-band configurations using Hustler MO-3 whip masts and resonators for 20 meters. Initially I supported this with a Radio Shack 19 ft mast set in the center of my back yard. While testing, I found that it was rather easy to work the Pacific Rim and the East coast of the United States.

 
     I constructed the test gig from two mirror mounts bolted to a 1/2" aluminum rod that was clamped to the top of the mast. I adjusted the resonators to equal lengths and for best SWR near 14.225 MHz. I used a 1:1 balun to drive both elements with about 50 ft of RG8X coaxial cable. The center impedance of this was nearly a perfect match for the 50 ohm coax, and a SWR of roughly 1.2:1 can be obtained by carefully adjusting the resonators. I used the RM 20 S resonators in this case, though, I suspect the RM 20 resonators would work equally well or better. Originally, I thought I would be perfectly happy working only 20 meters, as one of my main objectives was to communicate with friends on the east coast, and 20 meters is generally open to that region from California. However, 20 meters is a very busy band, and the QRM often wipes out communications with low power and simple antennas. So I decided to tri-band the system so that I could operate on 15, 20 and 40 meters. Originally, I had been considering making some traps and trying to use perhaps four of the MO-3 mast pieces, but a friend at Ham Radio Outlet in Burbank suggested that I use the Hustler VP-1 Tri-band Adapters which are inexpensive and require no serious modifications to the dipole configuration. I installed the Tri-band adapters on the end of each mast, and then installed the resonators so the the configuration was a mirror image on the left and right sides of the dipole. I used two each of RM 40 S, RM 20 S, and RM 15 resonators. I chose the S (super 1KW) series to get the greater bandwidth, but I am told that the standard resonators are slightly more efficient. So, here is the parts list and cost. Costs are based on Catalog Prices from Ham Radio Outlet and Radio Shack. If you don't need the zoom up mast, you can save some money. The machining costs are a significant part of the total. If you don't need the rotator, you can save even more, but rotation is a nice feature of this design and often makes the difference between working to station or not.

Item Model Number	Description	Number Required	Price Each	Total Price
Hustler MO-3	Mobile Mast Unit	2	$24	$48
Hustler RM-15	15 m Resonator	2	$25	$50
Hustler RM-20S	20 m Super Resonator	2	$29	$58
Hustler RM-40S	40 m Super Resonator	2	$36	$72
Hustler VP-1	Tri-band Adapters	2	$06	$12
Van Gorden Balun	HI-Q 1:1 Balun	1	$15	$15
Belden RG-8/X	Coax Feed Line	50 ft	$00.39 per ft	$19
PL-259 ST	Coax Connectors	2	$02	$04
UG-176S	Connector Inserts	2	$00.39	$01
RS 21-937	Mirror Mounts	2	$10	$20
RS 15-1225	TV Antenna Rotator	1	$65	$65
RS 15-5065	TV 19 ft Mast	1	$40	$40
RS 15-893	Vent Pipe Mount	1	$07	$07
PVC Pipe Expanders	Mast Bearings	2	$01	$02
Nylon Rope	Zoom-Up Rope	50 ft		$03
Misc. Machining	Zoom-Up and Mounts			$200
				_______
Total Cost				$616

Parts List and Break Down of Costs

Complete Tri-Banded Rotatable Dipole with Mast and Rotator

Adjustment of the Tri-band system can be a bit of a problem, as the final adjustments have to be done or at least tested with the support mast fully extended. It is easiest to begin by getting the resonators for the shortest wave length set first, as these have the least sensitivity to the other resonators. I adjusted the 15 meter resonators first, then the 20 and finally the 40 meter resonator. After some testing for SWR, it was clear that the performance was not as good as when I was using single or mono-band configurations. I had also moved the tests from the back yard to the balcony, so the antenna was much closer to the house and the metal gutters. I suspected that the problem might be that the left and right resonators needed to be adjusted differently. This turned out to be the case, and required several iterations of the adjustments to get the best performance. I also discovered after doing this that the antenna works better in the direction it was tuned, i.e., rotating it 180 degrees causes the match to change slightly, and the signals strengths change by nearly one S unit. The obvious solution to this problem is to get the antenna up much higher above the roof, however, this would make it visible from the front of the property and would surely be considered an eye sore by some members of the community. The idea, of course, was to hide this as much as possible.

  So here are the final properties of the tri-banded Hustlers fed as horizontal dipoles. The table below gives the SWR measurements as a function of frequency with the limits of SWR being 2.0: 1.

Band, Frequency

SWR

Bandwidth

15 meters, 21.080	2.0: 1
15 meters, 21.220	1.4: 1	260 kHz
15 meters, 21.360	2.0: 1
20 meters, 14.160	2.00: 1
20 meters, 14.225	1.15: 1	130 kHz
20 meters, 14.290	2.00: 1
40 meters, 7.160	2.00: 1
40 meters, 7.175	1.45: 1	30kHz
40 meters, 7.190	2.00: 1

Table 3

Properties of Hustler Whips used as Dipoles

 Note that the SWR is lowest for the 20 meter band. Also, note that these bandwidths are somewhat different from those published by Hustler, the 15 meter bandwidth is broader by about a factor of two, the 20 meter is comparable to the published bandwidth, and the 40 meter bandwidth is roughly one half of that expected. This latter difference might be partly due to the marginal 1.45: 1 SWR at the center frequency, however, this argument does not seem to apply to the 15 meter bandwidth. The photo below shows the antenna system and the associated zoom-up mast. Also shown are a few detail photos of the construction.

Detail of Triband Resonator

Detail of Balun, Connections, and Mounting