Mobile HF and which antenna

Discussion in 'On the Road' started by WD8G, Sep 7, 2014.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: HRDLLC-2
ad: Left-2
ad: L-Geochron
ad: Left-3
ad: L-MFJ
ad: abrind-2
ad: MessiPaoloni-1
  1. K4KWH

    K4KWH Guest

    Each has his own idea of "best". For RV's. I've seen screwdrivers mounted on TOP of Winnibagos (sic?), either slanted to the rear or forward as well. True, you may have a height problem with vertical mounting, but with some clever mounting solutions, the screwdriver is one solution to consider. If your body is fiberglass, it does not really degrade your signal. One I know of used to "stow" the antenna on top using a wooden "V" block. Mounted on a heavy swivel mount, the owner could stand the antenna UP while in a campground, for example, lay it down for travel--even use it in that position. One can also make a "half-dipole" to screw into the screwdriver coil. Using a weight tied to the other end, one can sling this wire (whatever random length suits you and allows you to operate on whatever frequencies you like) up over a tree limb. It will give you almost the same signal as a base station! Simply operate the screwdriver as per instructions.

    Again, everybody has their own ideas about mobile HF...and that's fine. You can tell that I am sold on the screwdriver because, over all, it will give you a better signal than most other solutions. :p Even the antenna "shoot-outs" give the screwdriver the edge. The worst performers were the hamsticks. (yuck!) I used to use various forms of bugcatchers; large loading coils with heavy wire and widely spaced coil turns. They did work well, except for the fact that, even tho their "Q" is high, often the very environment worked against them! Faced with the "fixed-tuned" status of the bugcatchers, it prevented remedying the situation on the spot. I lost a few QSO's because a big truck pulled beside me and screwed up the antenna tuning. DRAT! With the SD, It is just a matter of a little bump on the motor control switch, and it will account for the temporary anomaly and put the antenna right back at 1.2 to 1 SWR. The auto-positioners will do it automatically.

    Enjoy however you do it!:)
     
  2. AJ2I

    AJ2I Premium Subscriber QRZ Page

    I use Shark FM mini ham sticks (can get them at universal radio) for driving around and an MFJ-1979 while stationary. I wouldn't have it any other way. Save boats loads of $$$ on not having to buy a screwdriver and the believe the performance is the same...
     
  3. K4KWH

    K4KWH Guest


    What works best" is whatever suits the individual ham!:D If hamsticks work for you, then that's "best". Technically speaking, there's no way a ham stick can "equal" a properly installed screwdriver. Lots of antenna "shootouts" have proven that a screwdriver will not only outperform a hamstick, it will talk OVER a hamstick given the same power and conditions at the time, covering up the hamstick operator in the "mud"!!!:D Simple physics is at work here. A hamstick is basically a helically-wound coil over a small form. Coils can be "matched", or the natural impedance of the super-inefficient coil itself is sufficient to fool the radio into "liking" the presented 50 ohms. After all, you can wind such a coil (or resistor) @ 50 ohms, and it will load happily into it. Its called a "dummy load" and so long as the power requirements are sufficient, it will sit there, theoretically, for hours accepting a signal. What a hamstick does most efficiently is, dissipate heat. And that translates into a lower signal ouput. The screwdriver, OTH, has a larger coil (the larger the better), wound on a larger form, has better wire spacing (and wire diameter) and produces a much better signal. All these factors work to reduce resistance/heat. This is why screwdrivers use some sort of feedpoint matching to bring the total system impedance up to 50 ohms. There's no way, IMHO, a hamstick is going to "equal" a screwdriver. :D OTH, as you say, hamsticks are cheaper, and if it suits you, then it is the best for YOU!


    Yes, I am a huge advocate of the screwdriver, tho they are more expensive. But, for what most hams (and some other organizations [CAP]), the SD gives the most bang for the buck. Coupled with a good auto-positioner, the screwdriver is, IMHO, the best it can get for effective mobile comms. For those who do not need "the best", the hamstick is fine. A cheaper solution to HF mobile.:D
     
  4. K4KWH

    K4KWH Guest


    Delete dupe post
     
  5. WC5B

    WC5B Ham Member QRZ Page

    IMOP

    Monobanders like hamsticks and the hustler system are often going to out do any multiband option and at much less cost. If you need multiband however I would rate them as such:

    Stealth Antenna System > HiQ Antennas > Tarheel or Scorpion Screwdrivers > Outbacker Perths > Yeasu ATAS System > Anything with traps like the Comet line.
     
  6. K4KWH

    K4KWH Guest

    Initial cost? Yes. The hamstick is "cheaper". Technically outperform the screwdriver? NO. Too many "antenna shootouts" have proven that the screwdriver will talk over the top of the hamstick. Too many technical and physics reasons this is so. Yes. I do agree that if your budget will not include the higher cost Hi Q, et al, then, again, this IS the solution for you. For me, because I must cover a number of HF frequencies outside of Amateur Radio, because some of it involves life-saving, emergency, and air search activities, I must have the best output possible for a mobile, considering that any mobile is at a disadvantage at the get-go. I can't afford to have emergency traffic I can't get thru. One illustration of this hamstick versus screwdriver mobile: Our CAP wing (state) has used hamsticks for years for HF ops on vans. They were not successful, make low-band HF practically useless, leading some of the newbie ops to characterize HF as a noisy, unusable anachronism. They thought this was all HF could do as their inexperience gave them no other clue. I installed the FIRST screwdriver in OUR state on a mobile van. INSTANTLY it became the ONLY van that could call the statewide HF net near 75 meters, and do so reliably and effectively. It would also deploy to disasters, etc, set up and remain as needed on station, again providing reliable HF comms at all times. I made the half-dipole thing I could sling over a tree while stationary, and was able to take advantage of NVIS and the polarity of nearby stations operating at higher HF frequencies.
    This further enhanced the effectiveness and flexibility of our HF operations. That was what was required for the mission at hand. Again, if the hamstick/fixed-tuned Hustlers suit your purpose, then that's what is best for you: I am not knocking it!:D But a hamstick will not outperform a multi-band screwdriver on its best day!;)
     
  7. WC5B

    WC5B Ham Member QRZ Page

    I guess I would just have to disagree. I guess it goes down to personal experiences because I know of situations the exact polar that I have experienced. I actually ran both a Tarheel and hamsticks on the same big truck and the hamsticks were always the better talker. For obvious reasons I called the Tarheel the primary antenna for its flexibility however. Many things could have attributed to what you experienced however. The installation could have had a flaw in it of course but I may also coincide that a full size large screwdriver would be using higher gauge wire and noticeably out preform a hamstick on 75/80. It could also be that the hamsticks have a lower take off angle for whatever reason then the screwdriver you were using and allowed better state wide coverage. There is a whole host of reasons. Its not always as simple as one antenna is better. In that situation, that is why a lot of groups use a NVIS antenna that actually "degrades" the antenna so they can talk closer in. Like you say however, we do agree on important points. Hamsticks are great for getting on the air dirt cheap but screwdrivers are a much better option for there bandwidth changing. Hamsticks also degrade very fast in weather. You have too treat them as a consumable. That also could have been an issue. I never kept them over 6 months on the big truck. They just fall apart and stop hearing all together. When they work however, they work surprisingly well.
     
  8. HB9FUH

    HB9FUH Ham Member QRZ Page

    I have a whip+ATU combination on my Land Rover Discovery which works very well. I took as my inspiration the various Armies around the world that use HF radios vehicle mounted, they almost all do the same thing. So long as you ground the tuner adequately, what you bolt the antenna to is largely irrelevant. Out the tuner as close to the antenna as possible (the output side of the tuner is part of the antenna, and you don't want that snaking through the vehicle) and bolt the whip itself to the roof - you can happily have it anywhere between the horizontal and the vertical. Mine is actually on the rear quarter panel near the bumper (fender), simply because I couldn't mount the tuner any closer to the roofline.
     
  9. F5VHZ

    F5VHZ Ham Member QRZ Page

    If you want to have a HF mobile rig then you have to ask a few questions, when will I be using it, day night or any time.
    do i want short or big antennas, do I have a target zone or just want to work anyone anywhere...these should guide you towards some basic observations.
    If you want it to work any time then you need to choose a band that is always open..so out go, 10, 12, 15, meters, yes they work well but not at night.
    If you want good signals then heavily loaded antennas are out, so out goes 160, 80 meters. even 40 is a poor antenna for mobile and many have problems.

    The one band left is 20 meters and a 1/4 wave is only 5 meters so you can reduce the length with a high Q coil that will thump out a stomping signal that will get contacts with 59 ringing out all the time...and still have a good size antenna.
    This will get signals out over 1000 to 5000 miles and on the odd occasion you will get the other side of the world...and from a 100 watt mobile.

    I designed my own antenna, using a 1,5 meter base stub and a high Q coil wound in 6mm copper tubing 10 turns with even spacing ( gaps the same as the wire dia ) so that's 6mm gaps between turns. In all the coil winding wants to be 40% longer than the diameter. So for example if the support is 10 cms in diameter then the length need to be 14 cms, this will give the coil a high Q and allow maximum radiation from an antenna that will generate good voltages and currents..
    Next the two half's of the antenna need to be fixed to the coil. Simple and strong is the order of the day. So I chose a system of winding the coil for 20 meters on plastic plumbing fittings. and using end caps that screw in. U use a pl259 base connector and a N connector on the other end..why?
    Well the top half of the antenna is a very common glass whip used in many other antennas and it is 11mm dia at the metal end lug and is 2,1 meters long. I soldered a wire to the whip and inserted it into a N connector using the rubber seal to grip the whip and the wire is soldered to the centre connector as you would a coax..
    Next the lower half, this is made from any solid materiel that can carry the weight of the coil and top half. here I use another fibreglass rod with a thick centre wire ( to take the 100watts ) and a metal base with a screw thread to go on my standard antenna mount.
    This i cut at exactly 1,5 meters, as this will also be usable on the 6 meter band.
    Now the total length of the antenna is 3,6 meters high, it weighs about 1 kg and is very tough. dismantle able and you can even make a spare coil for 40 meters if you want using about forty turns of close wound coated wire. but the Q will not be as good as the 20 meter version it will still out perform most commercial 40 meter whips..and on 20 its amazing..
    That's why my design is called the BLACK WASP, it's black and has a sting in it's tail...
    AS you can see from the picture it looks great on my HALF SIZE landrover, and had been used on a variety of vehicles since i created it 7 years ago, ALpha Romeo 33 mounted on the towbar very low to the ground on an extender plate, on my landrover discovery either on a front bumper mount or on the roof bar. and on my Opel again on the towbar. The 20 meter band antenna has worked for me from france to get daily contacts with USA, Canada; Bresil, All Europe , Romania Russia, Iceland, even Japan and Australia and so many more, day and night.

    DSC09092.JPG S7000250.JPG Yes that's a half size replica not a landrover parked next to giant chairs.
    I know that there is no commercially available antenna that will out perform this home brew antenna. 3,6 meters high, covers the entire 6 meter and 20 meter bands with less than 1:1,3 swr and no tuner required. Cost about 30 bucks in parts. And in true ICOM style if I can hear it I can work it.. IC706MK2g my paddle mic, for CW and SSB see my qrz page for more info...
     
  10. K4KWH

    K4KWH Guest

    Perhaps at 20 Meters and above, the hamstick is the equal (?) of a screwdriver. At 40/75 meters? No way. I would point out in a previous post that we must not only cover statewide, but an 8-state Region and also communicate with stations in adjoining regions as well. Attempting to communicate with stations both far and wide with the "heliwhips" as they were called by the agency, was a total failure. When a van was equipped with a hamstick, the poor operator was simply humiliated by a very poor signal and unreadability. Given the mission requirements in *that* environment which included USAF and FEMA, the screwdriver style multiband antenna was an overwhelming success. The technical reasons are also mentioned in your above reply. A hamstick is basically a "dummy load on a stick" at 75 meters especially. The screwdriver has a larger coil with more widely-spaced turns/larger diameter wire--which reminds us of the garden hose analogy. IOW, to simplify, we are trying to force more water thru a smaller passage OR push our signal of whatever power thru small diameter wire (pipe). The helically wound coil-on-a-stick, instead of more signal, produces more heat & wasted energy. This is also why a hamstick will often load without any feedpoint matching, depending on its mounting and other factors. Mainly its that inefficient coil that often produces a 50 ohm match all by itself. Trouble is, it is also IN the coil itself and not at the feedpoint. A highly efficient (well, as efficient as it can be for a mobile antenna) HF antenna has a natural impedance @ the feedpoint of .......oh, 18 ohms or so. Without beleaguering the point too much, that big coil antenna must have some additional "help" at the feedpoint to get that desired 50 ohm match. That's why you see those toroids, capacitors or little coils at the feedpoint of bugcatchers, some Hustlers, and screwdrivers. Once the transmitter "sees" this 50 ohm match, it doesn't care if the antenna is "efficient" or not: it'll be happy!

    There's another advantage of the screwdriver and Hi Q antennas that gives them an edge. Unfortunately, the higher the efficiency of the antenna, the more sensitive it becomes to its surroundings. This means that your fixed-tuned antenna is subjected to a fluid environment that changes as your mobile goes along. The efficient antenna, tuned to a given frequency while stationary, then encounters trees, trucks, cars, metal buildings. Suddenly you are "detuned" and your QSO goes away. Plus your once flat SWR is thru the roof!!!! The screwdriver or Hi Q simply is re-tuned on the spot by an auto-positioner OR a bump on the motor switch to bring SWR flat again. Result? A more effective signal for a longer period of time and flexibility no other antenna can match. And, instead of a mismatched antenna and "tuner" combo, your antenna is operating at the true frequency at the best performance level it can give! For me, being that a mobile is at a disadvantage from the start, I want the best possible performance I can get at all times. I have also found that a screwdriver with a 3-4" coil works well and provides a great signal without passing the point of diminishing returns. It is possible to get TOO big with loading coils for 1) technical reasons and 2) physical reasons. There's only so much antenna you can have hanging out there.:eek:

    But once again, the "best" antenna is whatever suits YOU. If it gives the signals you like at a cost you like, then its "best". :D;)
     
Thread Status:
Not open for further replies.

Share This Page