Updated 18-Feb-2011 20:00
The mobile setup is an
There is an alternative solution for tuning the screwdriver that many have suggested… the N2VZ Turbo Tuner which searches for the minimum SWR coil setting. However a screwdriver antenna operating on 75/40 meters will require a matching network of some kind anyway since it is about 15 ohms resistive when the reactance is zero. The SDC-102 gets the coil in the ball park of resonance for the band or channel in use and the AT-7000 does the rest (I have two memories on 75 meters, one each on 60m, 40m, 20m, 17m, one for 15m thru 10m, and three MARS channels). Manual fine tuning can be done if necessary and optionally saved in a memory. This approach also allows me to use HamSticks or other fixed tuned antennas on the mount if required and use the AT-7000 to tune them, or plug the rig into a portable or temporary non-mobile antenna for emergency operations.
As mentioned above, the mounting mechanism can also be used for HamSticks which is what I used before installing the Hi-Q. My first contact with the 40m Ham Stick (using an FT-100D) in Oct 2006 was with W7MM in Philadelphia, I was parked just outside the garage, engine running! My signal was 59 solid, and the noise blanker totally eliminated any negligible engine ignition noise! Signals were as clear as a 2 meter FM repeater contact! We talked for about half an hour! I have since been able to use it to check into the USAF MARS net on 7.6 MHz while commuting to work at Hanscom AFB via I-84, the Mass Pike, and RT-128 near Boston… with the HamStick antenna resonated for 7.190 MHz, the AT-7000 easily tuned it for the 7.6 MHz MARS frequency. When the 75m HamStick is tuned to 3830 KHz, it can be tuned by the LDG AT-7000 from 3750 to 3975. I modified a 75m HamStick by removing 350 turns from the top of the loading coil to operate the MARS frequency near 4.6 MHz (perhaps better performance would be achieved by removing turns from the bottom?). I haven’t yet gotten around to modifying a 75 meter HamStick to work on the 3.3 MHz MARS frequency, and probably won’t anytime soon now that the Hi-Q is operational!
When I first installed the Hi-Q in May of 2009, I had some RFI feedback problems on 7 MHz that caused the radio to suddenly power off. I improved the choke balun on the coax by making sure it was located right near the antenna feedpoint and outside the vehicle (see K0BG’s web page, “Split Beads” and “Antenna Problems” topics), but this didn’t solve it completely. I then temporarily disconnected the screwdriver motor power and sensor cable and the problem went away, proving that this was the source of the problem. I then improved the choke balun for this cable by making a single loop around each of the 4 ferrites instead of just straight through the ferrites (see W6HIQ’s web page about this advice). I then made a ground strap from the antenna base to the car body to make sure the RF ground was solid. This STILL didn’t solve the issue on 7 MHz. Early in 2011, I finally made an L-Shaped standoff insulator from a piece of 2 inch ID PVC toilet pipe which I sawed to the appropriate shape and fastened with a hose clamp. (see the picture below for detail of its construction) NOW… finally I can work 3.2 to 30 MHz plus 6 meters without issue from the RF feedback. I think I’ll send an EMAIL to W6HIQ with my discovery, perhaps he will consider putting such an insulator on the antenna in the first place to keep that control / sensor wire away from the radiating part of the antenna. He took great care to insulate the screwdriver antenna and wiring to it inside the antenna radiating element.
The Hi-Q works perceptibly better than the HamSticks since I installed the Hi-Q so I no longer use them. One of my early contacts using the Hi-Q on 75m was with K2YN in Northern NJ who gave me a great signal report. Most stations I talk to on 75 meters don’t realize I’m a mobile station unless I tell them, so the Hi-Q claims for performance are not just simple hype. Perhaps in a really bad snow/ice storm I’ll take the Hi-Q off and use the HamStick as a backup!
IC-7000 Control Head Mounted with Velchro on the Dashboard of the Car
Ameritron SDC-102 Screwdriver Antenna Controller in Console Drink Holder
SWR graph of the Hi-Q with the AT-7000 enabled at the 75m operating frequency
Ameritron SDC-102 Controller with 10 memories for coil settings plus turns counter readout
IC-7000 Body and
Hi-Q 80/3 Mounted to Roof Rack, both Vertical and Folded Over
Hi-Q Quick Disconnect and Fold Over Mount Showing Details of the Choke Baluns for Coax and Coil Control Cable and Feedpoint
The right picture above shows a modification to the antenna introduced early 2011, an insulator which keeps the control and sensor wire away from the antenna to prevent RF feedback into the IC-7000 which shuts it down on 7 MHz. Following this modification, 7 MHz operation is solid as a rock and the RF feedback issue is gone.
Weather Cover for Hi-Q Quick Disconnect
This “weather cover” for the Hi-Q Quick Disconnect is made from a Rubber Chair Tip available at WalMart. They are intended for use as rubber feet on tables, chairs, stools, walkers, etc. and the size is 1 ¼”. Item name is SoftTouch by Waxman Consumer Group, Cleveland, OH. It is perfect for keeping the weather out of the quick disconnect when the antenna is removed from the car.