High Sierra HS-1500mkII And Turbo Tuner 2 Stall current ?

Discussion in 'Mobile Radio Systems' started by WQ6N, Oct 29, 2017.

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  1. WQ6N

    WQ6N Ham Member QRZ Page

    I have used my HS-1500MKII Screwdriver for a few years now. Love it. The first few years I used a AM-COM antenna tuner but recently I decided to get a Turbo Tuner 2 ITT for the IC-706mkIIg. I would like to know what others set their stall current to (750-100ma?).

    The First day, was met with the unit unable to achieve low VSWR.

    It took me a long time to get the AM-COM working and needed a 4 ohm 25 watt dropping resistor in series. Do
    I have the same problem with the Turbo Tuner 2? I am not sure what motor the HS-1500MKII Screwdriver has.

    I also had to play with RF chokes on the motor power cable. I think mix-31 did the trick.

    Anyway I am looking for constructive comments that might shed some light.
  2. W1JPG

    W1JPG Ham Member QRZ Page

    I've worked this problem with different equipment. I suggest asking simple and direct questions of the screwdriver and controller manufacturers. I had to get in touch with the Screwdriver manufacturer to get details of the voltage and amperage required by the screwdriver, and with the Controller manufacturer to get the controller to meet those requirements. They were both very responsive and helpful. Just today I received my fifth chip from the Controller manufacturer. I haven't had a chance to install it yet, but I'm hoping this one will do the trick. His initial max "slow up" voltage was too little to move the screwdriver. I needed full battery voltage. (It's a bigger screwdriver than he'd seen before. It tunes down to 160M.)

    RF chokes are absolutely required. k0bg.com has all the details about why, and how to properly choke. Here you can see the 5 3/4" Mix 31 split beads I use to choke the coax and leads running to my screwdriver. The coax takes half a dozen turns through each of the outer 2 split beads. The inner 3 beads choke wires going to the pulse sensor, power to the motor, and to a relay that selects between the 80 or 160M shunts.

    NL7W likes this.
  3. K0BG

    K0BG Ham Member QRZ Page

    You ask about current draw, but unfortunately, no one really knows which motor was used in your particular High Sierra. Nominally, if it is indeed a 12 volt motor (not a modified B&D rechargeable motor), the stall current will be close to 750 mils.

    Proper choking of the motor and control leads are essential. Information on those are on my web site. But this doesn't address the SWR issue. The High Sierra comes with a match coil built into its U-bracket. Problem is, it is to small and mounted too close to the bracket. Nonetheless, it should work okay, but since we don't know how and where you mounted your antenna, the case is almost moot. So the first question is, do you own an antenna analyzer? If so, follow the directions in my matching article for help. If you only have an SWR bridge, or using one built-in the radio, you're in for a bit of work. This issue to is described.
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    How can stall current on a DC motor be less than operating current ?

    Just curious.
  5. K0BG

    K0BG Ham Member QRZ Page

    It shouldn't be. The nominal current draw (running) of the top three screwdrivers hover around 250 to 300 mils. Stall current is about 2.5 to 3 times that level. Other vary. Larry's antennas, for example, use a modified Harbor Freight gear motor from a rechargeable drill. Their run current is about 2,500 mils, with stall current nearly 8 amps! This is more than a TurboTuner will handle, and outside the normal operating range of all but one controller.

    My personal Scorpion SA680 draws 250 miles going up (lower frequency) and 200 mils going down. Stall current is 650 mils. The Pittman motor is rated at 17 volts, and is symmetrical. To explain that... Most small gear motors are designed to run one direction only. To increase torque in the designed direction, the brushes are offset a few degrees toward the direction of the rotation. Hence, they have more torque turning in one direction. Unfortunately, most manufacturers select the least expensive ones, and in a standard screwdriver configuration, that means the max torque is when the antenna in retracting. It should be the other way around!
    AK5B and KA9JLM like this.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    OK Alan Thank You, That makes perfect sense.

    Sometimes it is best to think about Power limit in Watts, Instead of Current limit that is specific to a certain voltage. That works for me if max voltage is not exceeded.

    I have never screwed around with a screwdriver antenna. It does sound like Fun.

    Last edited: Oct 29, 2017
  7. WQ6N

    WQ6N Ham Member QRZ Page

    Thank you for the pic and comment. As you probably know , HS is no longer in business due to the reported owners health issues. I have been in communication with the Turbo Tuner 2 tech but they are not familiar with the HS1500mkII antenna or dropping resistors for that matter. I took the remote apart that came with the antenna and it uses a 2 ohm 15w in series with a 1 ohm 5 watt resistors. So, I did purchase a 3 ohm 25w from Fry's and it appears to be just right.

    Your RF choke setup goes well beyond what I have put together. Basically I was just using the same setup that I used with the AM-COM controller. Currently the antenna moves about 1/2 inch before stopping with "unable to achieve low SWR" alert (Three T's on the Turbo Tuner 2).
  8. WQ6N

    WQ6N Ham Member QRZ Page

    The motor for the HS1500mkII is a HS factory wound motor that is not 12vdc. The antenna is pre-Black Hawk motor mod associated with the HS1800Pro series. Yes, I have an analyzer and have manually tuned/marked the antenna to low SWR (1:1.2 nominal). The antenna is mounted rear of the car via a center trailer hitch (typical). I use a 1 inch solid copper strap to the frame from the HS mount. The coax, from the HS antenna mount to the TT2 tuner, is RG-214 with a single choke within 8 inches of the antenna mount connector. The motor lead is also choked with a single toroid near the antenna. I am thinking of changing the coax to RG-142 and incorporating multiple choke points. The coax from the tuner to the 706 is a short length of RG-214 with no choke. The power lead from the 10awg 12vdc supply to the 706 is not choked.

    I will take a look at your web site. Thank you for the comments. You are spot on regarding the base loading coil.
    Last edited: Oct 31, 2017
  9. K0BG

    K0BG Ham Member QRZ Page

    Low mounting, trailer hitch in this case, increase ground losses significantly. As a result, the input impedance will increase, and the SWR will decrease to the point you might not need a matching coil at all. As for the copper strap, although it provides a partial return for the RF current, it is not a replacement for a meter mass directly under the antenna.

    I'm a bit confused with your statement about a tuner. If screwdriver antennas are matched correctly, as "antenna tuner" isn't required. Perhaps you were speaking of the antenna controller? In any case, a common mode choke should be installed on both the coax and control lines. This is extra important because of the mounting location—increased ground loss equals increased common mode current.

    I wouldn't use RG142 (or RG214 fr that matter). It is about 6 times lossier than RG58, much less RG213 or RG214. Further, since we're speaking of very short runs (≤10 feet), RG8X is only about .2 dB lossier than RG214, and a whole lot easier to work with. Oh! And treat that IC706 with care, as proprietary parts (final, driver) are nonobtainium.
  10. WQ6N

    WQ6N Ham Member QRZ Page

    Yes, on the antenna controller naming convention. I do have a mix-31 toroid about 5 inches from the motor connector. I did read your article and may try a different wrap or even stacking a couple in series. Any idea on why the antenna controller would only move the screwdriver antenna only 1/2 inch before shutting down with each tuning attempt? I am starting to think that the TT2 is only for 12vdc screwdriver antenna motors and may have to return the unit if so. At least I know the AM-COM controller works to some degree. So much for a turn-key upgrade.

    Roger on the "nonobtainium" advice, I have read this on other posts. Only 70% max output is used here.

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