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The KV5A Mobile Whip Project

featuring the

KV5A Power Whip

Latest UPDATE 12/21/2017

If you have built this antenna or one similar, please tell me your experience. 

(To enlarge the pictures right click on the picture and open them up in a seperate tab or window.)

I built this high performing antenna in July and August 2014 made from copper plumbing pipe and fittings with a bit of PVC, polycarbonate, stainless steel hardware and a 102 inch whip and a few other misc items. It features easily changed center loading coils and can be driven with a high power amplifer.  Mounted on the back of my Ford F150 truck bed, the KV5A Power Whip performs just as good as anything I think I can buy and it certainly is a whole lot less expensive.

    KV5A Mobile Whip installed on a 2013 Ford F-150 PU 

Many of the screw driver antennas on the market todat will not safely accept more than 200 watts of power. Thus my quest for an antenna that will allow me to safely use a power amplifier for mobile HF operaton. I have an ICOM 706MIIG and an Ameritron ALS 500M 500 watt Solid State amp mounted under the rear seat of the truck. The coils I fabricated are for 75, 40, 20, 17, 15, 12 and 10 meters.  The 10 and 12 meter bands requires a shorter whip of 56 inches, however.  Each coil varies in dimensions optimum match and bandwidth reqiuirements. The 40 meter coil provides a good match for half the band. Using two coils tuned for high or low band operation provides full band operation. The 75 meter coil is High Q and very narrow in banwidth and centered at about 3939 kHz for my use. 

 Amplifier and exciter instalation.   

This antenna will tune to 6 meters using a shorter stinger and a dead short in place of the coil for a full antenna length of 4 feet 8 and 1/2 inches.

The Power Whip is a non-screwdriver antenna and has no moving parts.  It is relatively efficient for a mobile antenna.  It requires a pit stop along the road to change bands. It takes just a few seconds to pull one coil off and install another. No tunning is required. The tunning is accomplished during the initial installation of the 75 and 40 meter bands. All other loading coils are pre-tuned.  The KV5A power whip as installed on my truck is just under 15 feet from the ground to the tip of the stinger. Overall length is 11.5 feet from the feed point to the tip of the whip. Some low overhead bridges and tree limbs are going to hit the whip while on the road so, for safety and to prevent antenna damage, you can tie down the whip to a lower overall height by securing a parachute cord to the whip and tie the other end of the cord to a tie down fixture on the bed or trailer hitch. This may change the SWR, so check your match after lowering the end of the whip. 

 The whip in tie down position.

So far, my on air experience with the Power Whip is quite pleasing.  I consistantly get comments of "great signal for a mobile".  Okay, it's all relative of course, and band propagation will dictate signal reports. This antenna mounted on a truck like mine will ride just fine as long as you mount the feed point low and install an insulated bracket support at the top of the bed as shown below.  This prevents stress on the feed point and keeps everything tight and right. 

This mobile antenna project is now near a final design.  The antenna simple and robust. This design meets my goals of simplicity, high power capacity, low cost, high performance and reliability. There are no moving parts to break or wear out.  Quick change pre-tuned center loading coils for each HF band is eliminates tuning when changing bands.  The quick change pre-tuned loading coils have proven to be a big winner for my operation.  A shunt coil at the feed point will drain static buildup to ground and increase the driving impedance for better effiecency.  The coil assemblies are painted with black enamel paint for corrosion protection and to give them a finished professional look. 

 The feed point and shunt inductor.

   Installed and ready for fun.

The tension of the banana jack and plug connection for each coil is strong enough to keep the coil in place while mobile but just in case it gets whacked by a tree limb or vibrates loose, I install a bunjicord around the coil and plastic plate.  While this antenna might not be suited for every need or be easily mounted on some vehicles, it certainly will work great mounted on pickup trucks like mine. If the loading coil is not close to any metal on the truck body and the feed point is within a few inches of the bed floor and secured as shown above, there should be no problems with detuning.  HF mobile operation is a blast especially on long trips across the country.

          40 meter coil and mast.          

Below is the data I collected on October 30, 2014 for the antenna impedance and the 2:1 SWR frequency for each of the bands loading coils.  I used a MFJ 259C antenna analyzer and a one foot of coax cable attached to the antenna feed point A 102 " whip is used on all but 12 and 10 meters when a 56" whip is required. The following preliminary data is presented subject to change.

75 meter Coil  (1st prototype) SWR 2:1  span is 3927.6 to 3946.8 KHz (19.2 KHz) @ 3939.0 KHz  R= 30 X= 0

40 meter Coil (2nd prototype) Improved SWR 2:1  span is  7.098 to 7.178 MHz (8KHz) @ 7.180  MHz  R=25  X= 0

20 meter Coil SWR 2:1  span is  13.733 to 14.770 MHz @ 14.235 MHz  R=49  X= 2

17 meter Coil SWR 2:1  span is  17.29 to 19.00 MHz @ 18.15 MHz  R=50  X= 2

15 meter Coil (needs work to optimize) SWR 2:1  span is  19.760 to 22.581 MHz @ 21.155, R=60 X=8

12 meter Coil @  24.96 MHz  R=31  X= 0  -56" whip

10 meter Coil SWR 2:1  span is  26.9  to  30.0 MHz @ 28.0 MHz R=36 X=0 @ 29.7 MHz R=59 X=23 -56" whip

73, Dave

8538826 Last modified: 2017-12-27 16:17:14, 11392 bytes

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