|Cushcraft R5 ½ λ Vertical||Maintenance and Repair|
CUSHCRAFT R5 (10/12/15/17/20 m)
Cushcraft have made many vertical antennas; R4, R5, R6, R6000, R7, R7000, R8 etc. All are ½ wave radiators with 4 or shorter base-load rods. Those “radials” are in fact a top hat capacitance. The quality of the R6 successors decreased, see Product Reviews on
The 17ft half wave vertical is covering the 10, 12, 15, 17, and 20m amateur bands. The antenna does not require traditional ground radials, so no need for unsightly radials and is so light a normal scaffold pole would be ideal to mount the antenna.
The manual states that this shortened half wave radiator is suited for 1.8 kW pep power and that is remarkable for this type of 5 m-tall antenna. The vertical passed a test with a borrowed 1.5 kW amplifier with no-ill effect. There were no signs of failure on the traps or matching unit.
R5 a 5 band vertical on top of a 12 m mast.
The R5 is mounted on a 12 m mast. My 2 el. Yagi only outperforms this antenna if the beam is pointed to the station. The difference is very noticeable in SSB/CW DX pile-ups, but if I can hear them I can work them. It provides useful DX performance. I did comparisons with my open wire fed inverted V W3DZZ and on 20 m: R5 = W3DZZ at 1500 km. On all bands beyond 1500 km the signal strength is about 1 S unit better than the W3DZZ.
This antenna is very usable and, being asymmetrically fed, with no radials and only 4 × 1.24 m stainless steel whips («fig) is attractive for apartment dwellers. All hardware is aluminium or stainless steel. The aluminium durability is good but not as good as Fritzel’s tubing. It has withstood many heavy windstorms without a problem and currently is bent over at about a 10 – 15 degree angle. It is rugged and not too tall mounting without guy ropes. This antenna is sensitive to metal objects in near field. Prevent installation over a metal roof or near out other antennas because they will detune the R5 considerably.
Fig a: A bare weather beaten insulator.
Fig b: An unprotected new R7 insulator.
The fibreglass base insulator (fig a) is a polyester-coated tube. The polyester surface has the tendency to “evaporate” and the bare glass fibres then are like a sponge attracting absorbing dirt and moisture.
The insulator was “painted” with layers of 2 component polyester resin and sprayed (fig») with “bumper spray”, a black non-metallic spray paint. It prevents the deterioration of the polyester.
Insulator protected with black non-metallic spray paint.
MATCHING NETWORK R5
L to R: choke balun (brown colour wire) and 1 : 4.84 auto transformer (black and white colour wire).
The matching network is composed of a choke balun and auto transformer. On several homepages the transformer is called a 1 : 4 balun. That is contrary to the print design.
I don’t know if the manufacturer designed it as such, but as it is mounted on the PCB it works as an auto transformer with a ratio of 1: 4.84. All matching networks that have been reviewed here shows equally designed print boards. You can see that 5 black turns and 6 white turns are through the core. So the transformer step up ratio is 5 : (5 + 6) and that is an 5² : 11² = 1 : 4.84 impedance ratio. The 50 Ohm input is transformed to 50 × 4.84 = 242 Ohm. The schematic of the circuit was drawn by following the mounting of the components on the circuit board.
With a suitable antenna tuner one could also use a R5 on more than five bands and even on 80 m! If that happens with a lot of power, then the right picture shows what the result is. Both toroids cannot handle the mismatch, getting hot in a very short time and then burst!
I replaced («fig) the two 86 pF caps in series with a single transmitting high current 47 pF doorknob type.
MATCHING NETWORK R6, R6000
The auto transformer of an R6 is different. The white wire goes through the core 12 times and the black wire 9 times. The input (50 Ohm) tap is at 9 turns of a coil with 21 turns. The transformation ratio then becomes 1 ÷ 5,444. The 50 Ohm is thus transformed to 50 × 5,444 = 272 Ohm.
MATCHING NETWORK R7 & AV640
By coincidence, I found a matching network of an AV640 or R7 on eBay. With these antennas, the number of radials (= end capacitance) has increased and the 40 m band requires more self-inductance. That is why two stacked toroids have been installed for both the choke balun and the auto transformer. Given the number of turns of the transformer (10t + 12t), the transfer ratio is 1 ÷ 2.2 and impedance step up 1 ÷ 4.84. The system transforms the 50 Ohm asymmetrical impedance to a symmetrical impedance of 50 × 4.84 = 242 Ohm.
This matching network was also obtained via eBay. Between the choke balun and auto transformer an 27 pf capacitor was connected in parallel as was the case with an R5. This capacitor was probably added to improve the SWR on the 10 m band. The choke balun has two stacked toroids and for the auto transformer a thick core is installed. Given the red color, it is probably a T200-2 type.
IF required, ring cores can be replaced with the following types:
Choke balun: FT240-43 or FT340-43.
Auto trafo: FT240-K
The traps should be carefully loosened and the contact area and all other aluminium hardware should be cleaned with Brillo pads (steel wool impregnated with soap).
Water got inside a trap due to cracked heath shrink tubing.
Cleaned and repaired coil
I have been using my 2nd hand R5 for more than two years and then some problems arose. The SWR was varying and increased on some bands. I took the antenna down and it turns out that water got inside a trap because cracked heath shrink tubing and a split in the joint between the coil former (force-fit?) into the aluminium tube. The heath shrink tubing was carefully removed and the coil, covered with “transparent contact adhesive”, was cleaned with thinner.
Once clean, the split should be filled with epoxy glue (2-part polyurethane adhesive), the coil buttered with transparent contact adhesive and reassembled with heath shrink tubing. The process with the transparent adhesive is for preventing that water gets inside the trap.
Leaking spots are the heath shrinks tubing over the bolt onto the connection of the coil former with the tube.
The capacitors paralleling the sealed coils are coaxial types with a rod, a tube and a dielectric tubing in between. One end is sealed with heath shrink tubing and the other end is protected with a cap.
One capacitor failed because of a burst cap and water get into the coaxial system. This changed the dielectric constant of the capacitor, thus moving the resonant frequency, and the SWR increased dramatically. Flash-overs when running high power shorted the wet capacitor out and evaporated a part of the insulating tubing.
This was replaced with a short piece of PTFE tubing and all of the components were dried, cleaned and reassembled with contact cement and heath shrink tubing.
It seems that glue sticks («fig) for a glue gun are suitable for replacement of the insulating tubes.
All caps are replaced with («fig) rugged caps.
All R5 parts of the 1989 model.
Measuring the traps is only possible by comparison with another R5. Make sure that you do not touch any part of the antenna and vary the frequency of a (grid) dipper meter until a strong dip is seen. Move the meter away while retuning until a very shallow dip is seen. Take note of the trap frequency. Repeat this process with the repaired R5.
The assembly and installation manuals of 3/1989 and 10/1989 show different dimensions for the radiator.
With the antenna on a 2 m mast I measured the SWR, on each band with a half wave (or multiple) 50 Ω cable for that band between the feeder point and an analyser. I found the dimensions in the schematic by varying the sections to match the specification
s for SWR ~ 1.
Back on a 12 m mast the R5 performs by ½ – 1 S unit better (75% of the QSO’s) than the inverted V W3DZZ.
With a 12.5 m 50 Ω coax cable feeder line the SWR was:
NOTE: 2 TYPES OF TRAPS FOR 15 m and 17 m
Combined 15/17 m trap March 1989
15 + 17 m traps October 1989
My R5 was suited with approximately 12 m coaxial cable (AIRCELL 7). The length includes a choke balun at the beginning of the cable and the SWR at that point is shown in a table.
The SWR can increase considerably at the band limits and that can be a problem for modern transceivers without an antenna tuner. Here a tuner is always used for all antennas and so also for an R5 see the next topic.
I use an easy to build
pi-ATU to always ensure that the transceiver is loaded with a SWR = 1.
The antenna wobbled due to the gap caused by evaporation of the polyester. The tube was removed, the inside of the insulator applied with layers of 2 component polyester resin until a minimum variation of fit. Then I sanded the insulator for a perfect cylindrically curved shape and applied the last layer and placed the antenna back in the insulator. In fact the insulator was restructured to its original diameter.
I used a polyester repair set (for automobile) and applied the 2 component polyester resin with a brush. Eventually fill holes with fibreglass. The 2 component polyester resin can be used in combination with fibreglass mat and fibreglass thin film to fill holes in surfaces of steel, aluminium, wood, concrete and polyester. Polyester resin is elastic and resistant to chemicals and weather influences and is, after hardening only sand smooth mechanically.
Due to the gap the antenna wobbled and one of the straps was broken.
I replaced a shortcut 27 pF cap with 4 × ceramic tube caps in series/parallel.
Greg, W9GB found a potential replacement source for damaged MN-7 black enclosures.
He wrote: “I have found the a black plastic case (fig») that is identical to the MN-7 Matching Network enclosure used by Cushcraft. It appears that Cushcraft used the Polycase “EP” series, EP-8 model. The POLYCASE® EP-8 size is identical and injection mouldings from the dies are identical in every detail to my MN-7 (1992). I do not think Polycase makes the “EP” series currently. These EP-8 boxes are now surplus NOS from Electronic Surplus, Inc. (ESI) in Cleveland. OH. ESI had 441 in stock at $ 4.50 USD each — I just received 3 to confirm match”.