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Mobile HF and which antenna

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

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  1. AJ2I

    AJ2I Premium Subscriber QRZ Page

  2. KD0SGX

    KD0SGX Ham Member QRZ Page

    Just use a 40 meter hamstick. This was a 20 meter one, same size.
    [video=youtube_share;xAmCA-6I2bA]http://youtu.be/xAmCA-6I2bA[/video]
     
  3. KD8ZWI

    KD8ZWI Premium Subscriber QRZ Page

    This sounds rather interesting, a couple of questions:
    1. you seem to be describing running the Antenna inside the trunk? Nothing outside the vehicle?
    2. Hustler makes serveral antenna - which one are you using, and do you get 40m, 20m, 6m performance?
    3. Can the AH-4 be used with a Yaesu 857d?

    Thank you for your informative post.
     
  4. K4KWH

    K4KWH Guest


    I'd have to disagree with "TRUE ANTENNA TUNER". There is no such thing! While it *may* match the feedline and do everything you say, it does not "tune" the antenna to ANYTHING. Anytime you have an antenna that is, by itself, at one frequency, its natural impedance is not 50 ohms, it is NOT 'tuned". When your AH-4 is fooling the radio into thinking it has a 50 ohm match---and it DOES, your system is NOT an optimum system. You can take a 50 ohm resistor, put it across the antenna terminals, and "load' it. The radio will sit there, putting out its signal for whatever time is reasonable. Likewise, you can stick on a hamstick on 75 Meters, and it will often work "fine"---but your signal will be poor. Your "signal" is being absorbed by that wonderful coil that does a fine job of "loading" because the radio is tricked with an apparent 50 ohm match. Fancy explanations of "why" it is matched don't matter & the radio don't give a .......well, you know!:eek:;)

    The only mobile antennas that truly are "tuned" are screwdrivers and the Hi Q, either with built-in positioners, OR those who are monitored by the operator and positioned manually. Remember these are POSITIONERS, NOT "tuners" because they move the antenna to actual frequency of operation. This gives the best performance available in a mobile, particularly because they take into account the fluid environment in which the mobile antenna is moving. Fixed-tuned, single-frequency antennas with taps and jumpers STILL have disavantages because they are never truly "in tune" at a given moment, even tho they may be theoretically highly efficient! :confused: The higher the "Q" of the antenna, the worse these affects are because the given SWR conditions at a given time, at a given location are not under the control of the operator. It is the mobile screwdriver and the Hi Q genre that eliminated most of such problems.


    "Tuners" do NOT "tune" antennas! ;) To each his own, but I don't believe much in mobile so-called "tuners"! JMHO!:D:cool:
     
  5. KC0MS

    KC0MS Ham Member QRZ Page

    I have read what most of the experts have to say on mobile setups and find myself still at the mercy of what I need to do in order to have a decent antenna, and a happy rig.

    For example, one expert suggests that a "resonant" antenna may not indicate a satisfactory input impedance due to the obvious mismatch such a mobile antenna provides....and the "solution" to that particular dilemma is to affix a shunt coil at the base of the antenna....along with such caveats as do not have the antenna go through the shunt coil, and do not have the shunt coil around any metal surfaces.

    Well, duh!.....if it is a mobile set-up, then in 99% of the installations, the antenna IS MOUNTED on a metallic surface.

    Then there is one where measurements should be taken by an antenna analyzer as close to the actual feedpoint of the antenna as possible....the caveat being, do NOT stand close to the antenna or the analyzer, as doing so will affect the reading.

    Again duh!....so what is the op supposed to do then?.....climb a nearby tree and use binoculars to read the meter?

    I personally use very inefficient Hamsticks and Hustler antennas for all my mobile work, with reasonable and satisfactory success. Sure I could probably gain at best a half an "S" unit with some big monster of an antenna....but at up to 700 clams to do so, is not my idea of cost-effectiveness.

    I have adjustable "whips" for each of my antennas, which I manually "tune" for best compromise between resonance and impedance and then employ a transmatch to reduce any residual standing wave down to keep the rig happy.

    And it works. I know some experts hate it when an op uses how many DX stations they contact while mobile as any kind of yardstick to measure mobile efficiency, and getting worked all states while mobile....but SOMETHING must be right in order to do that, right?

    This mobile subject can literally be beat to death, and an op can beat themselves to death attempting to achieve results out of something which is already admittedly a poor compromise to begin with, what with all the statistics being bandied around.

    I've said it once and I'll say it again......even with a cheap-azz 15 dollar Hamstick.....on a properly grounded and bonded vehicle and mounted someplace near the center of that vehicular groundplane, you will achieve results which should please you to no end.

    Ok, flak jacket on and running for cover....
    73, Karl
     
  6. KG4NEL

    KG4NEL Ham Member QRZ Page

    Not to sound snarky, but...so?

    The problem in getting an AH-4 to load on 75 is the infinitesimally small fraction of the wavelength that radiator presents at 3.5MHz, not any deficiencies in the tuner itself or the concept. If someone wanted to carry around a quarter-wavelength of aluminum tube and make a 40m vertical when parked, that'd be just fine.

    His point - that it's better to put the tuner near the feedpoint, or at least with as least loss between the feedpoint and the tuner output - is sound.
     
  7. K4KWH

    K4KWH Guest

    I can't disagree with that! All such solutions for HF mobileering are satisfactory IF it suits the operator. The physics are what they are; can't be changed. But this is why there are so many products on the market attempting to solve the problems of operating HF mobile. And, a lot of it is a matter of opinion as to what is "best". HF antennas are "scrunched" and crunched down to some manageable level and some sort of trickery must be employed to get it to work. Me, I don't mind the "Big Ugly" antenna hanging out there, and I have no XYL telling me I can't put "that ugly thing" on the new "Shiv-o-lay"!:D So I opt for what works for ME. To each his own!:cool:
     
  8. W8LM

    W8LM Ham Member QRZ Page

    I too use an IC-7000 and AH4. Trunk mounted in my new Mercedes C250.. I travel 30,000+ miles every year for my company. My HF mount is an 1/4 inch steel 2 inch wide strap.. 15 inches long. I bent it into an "L" shape (vice and a torch) and popped a plastic grommet in the spare tire well, and use an 1/2 bolt to secure it so the end sticks out from under my bumper. I then use a 3/8" base mount and ham sticks. I carry 80-40-20 hamsticks in the trunk. All tune all bands with the AH4 antenna tuner. Between the tuner and the ham stick, I use about 8-10 inches of RG8/U minus any shielding. That can handle 5-6KV easy as base voltages can be high. the RG8/U center conductor goes through another grommet in the body. for V/U I use a dual band antenna and a Larsen NMO trunk mount center of trunk at the rear windshield. The mercedes has a fuse panel in the trunk so my IC7000 connection to the fuse panel is 15 inches long. The control head sits on aluminum brackets I fabricated to the ash tray that I do not use, in the center console. the radio control head sits just north of the shift lever, and the shift lever makes a nice wrist rest for spinning the VFO dial. When I remove the rig and antennas there will be a 1/8" hole in the ash tray, and a 1/4 inch hole in a water plug grommet in the trunk. Both easily repaired with black epoxy and will be invisable when I trade it in. Now, I had to stay out of the roof because of the moon roof and air bags. The days of drilling a hole in the roof of a new car with only 7 miles on it are over... Yes I did drill a hole in the center of the roof with only 7 miles on the vehicle. 12 years ago and I still own the truck..

    It took me an entire saturday to fabricate, assemble and install it all, but it's professional and done right. Tywraps, and all crimp connections soldered. all bolts have star washers. Don't scrimp - about the hamsticks - I wanted something that when standing 20 feet from the car you can harley see. I also wanted to start with an antenna with low wind resistance as I was unsure of what my "L" shaped bracket would do when traveling at 65-75 mph for hours. In the future I may mount a HI-Q antenna I have.. However it's size means a mounting more substantial than I currently have.. All my 20-30 years of mobiling, HI-Q antennas are the best I've used. Hi-serria have fallen apart in less than a year. The advantage of the HI-Q is that the antenna is the tuner. Yet at one time used a 20m hamstick and a FT-817 5 watt rig mobile to work england, france, germany, and south africa from New England.

    BTW - the C250 is averaging 33mpg ighway on the trip with those antennas The mercedes has very little ignition noise, and DSP takes it out if needed. Actually I have only hear ignition noise while idling and looking for it; not at highway speeds. Compared to my last vehicle a Hyundai Sonata Hybrid which got only 32 mpg highway, and had s9+10db noise on all HF bands..rendering it a trade in for the mercedes. Foreign cars and dealerships do not understand RF interference some specify no 2way radio's installed over 3 watts!!

    I am in the middle of a Wichita, Kansas to Hampton Falls, NH Christmas venture. I'm over 2000 of a 4000 mile 2 week long trip. I have worked Italy on 20, On 40 I have worked 400-700 miles during the day. 80 night time over 1000 miles. The 80m hamstick and AH4 tuner does tune 160 but I have not tried a QSO there yet. Most of my drive time is 8am to 8pm.. However post christmas I will pull an all nighter drive from Rochester, ny to indiannapolis, so I may try late night 160 meters.
     
  9. K3MP

    K3MP Ham Member QRZ Page

    I have been running a Comet UHV-6 HF/VHF/UHF antenna for years ... I only use an old Icom 706 (original) 1993 ... and I do use a LDG Z-100 tuner with it ... it has given me many great reports .. I like it so much I bought another one for my RV that I had at that time ...
     
  10. K1LOS

    K1LOS Ham Member QRZ Page

    Hi folks. I am a new ham (tech class) and am trying to setup my 1st system in my RV. I hoping to do a bit of future proofing until I get my general by building a system that is also very HF capable. I have been searching the net for some good advice on antennas and systems and am strongly considering the IC706MKIIG (alternative suggestions appreciated). The main question I have is about the antenna(s) for my RV. The RV is a newer class A (bus) Winnebago which means it has a mostly fiberglass shell over a large steel framing structure. The RV is already 12 feet tall and I struggle to get under many trees and bridges. Bumper mounting a steel whip seems like a bad idea since most of it would run parallel to the steel frame. The roof being fiberglass does not seem to be a great ground surface but for the widely spaced steel cross members. I did glue large sections of flat aluminum to the roof to mount my solar panels and could do the same for my radio antennas. The roof has plenty of horizontal space but adding much vertically will be a real problem. I am not afraid to run multiple antennas and would like to get "decent" mobile HF capabilities, as well as UHF/VHF. Any suggestions on off-the-shelf antennas would be greatly appreciated! I am not quite ready to get into home-brew.
     
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