Cushcraft R7000 Vertical Antenna

The Cushcraft R7000 is a multiband vertical antenna rated at 1500 watts peak power, 1000 watts continuous, on the 7 through 28 MHz amateur radio bands. Interestingly it also exhibits low VSWR on 6 meters. KP4MD performed analysis on the previous Cushcraft multi-band antenna, the R7, which inspired me to update his analysis to the R7000. Modeling was done with the 4NEC modeling program.

Many refer to this antenna as a half wavelength end-fed antenna even though it's physically less than a half wavelength on most of the bands it covers. In fact it is more like a 3/8 vertical with the normal 200 ohms +Jsomething (inductive impedance). Electrical length on each band is determined by the traps which also act as loading coils on some bands. The matching network has a 4:1 Balun and RF choke. For matching network details see EI7BA's page on the R7. The capacitance to counteract the +Jxx inductance is achieved through the 49 inch "radials" which are not radials at all but form a capacitance "hat".

Accurate modelling required insight into the construction of the traps. Having recently moved my own R7000 I had no desire to to take it back down to disassemble and measure the traps. Luckily I found an excellent article by AA4LR on rebuilding the R7000 that contained the necessary physical details to build my model. The Cushcraft manual states that the antenna must be mounted at least 6-8 feet above the ground. Not contained in the manual is the fact that the design height of the antenna is 18 ft. (second source on this info). In my location I need to get as high as I can to overcome hill blockage in almost all directions except South and West. I ran antenna patterns on all bands at both the design height of 18 ft and my installed height of 32 feet to see the effect of antenna height and look at the main lobes compared to my horizons.

I was expecting the design height to have well behaved low angle lobes. As the antenna is raised you would expect higher angle lobes to appear. For the most part this is true and is most evident on 30 and 40meters. However on 17 and 15 meters is appears that the 32ft height increases performance at lower angles.

Right-mouse-click/alternate-mouse-click on the link below and select "Save Target As" from the menu to download to doload the 4NEC model configured for a height of 18feet Download 4NEC Model


                    Photo                          Manual Schematic                             Dimensional Model                                           As Modeled in 4NEC2

     






The results

              18 Feet                         32 Feet
40 Meters

30 Meters

20 Meters

17 Meters

15 Meters

12 Meters

10 Meters

6 Meters