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Portable HF vertical

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N1RVN, Sep 7, 2017.

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  1. N1RVN

    N1RVN Ham Member QRZ Page

    Still relatively new to HF so go easy on me...

    Trying to put together an 80-10 meter portable quarter wave ground plane HF antenna using a Wolf River Silver Bullet 1000 loading coil, a 17-foot telescoping whip as radiating element (MFJ-1979) and four wires sloping at 45 or so degrees for ground plane. I'd like to have the base of the antenna at about 6 feet so I can access the loading coil - better yet, use a telescoping pole as support so I can reach up to shorten the whip for higher frequencies. Possibly using an "extension rod" below the loading coil to increase radiation efficiency.

    This would be used with my Yaesu FT-891 at up to 100 watts, not necessarily lightweight setup, more like "close by the car" in a park or on vacation. The 891 doesn't have a tuner - I would prefer to tune the antenna, and I have the RigExpert analyzer for that.

    Will this work? What length should the ground plane wires be?

    Metal or non-conductive support?

    Any constructive comments welcome.

    Thank you,
     
  2. VK3YE

    VK3YE Ham Member QRZ Page

    10 MHz and up should be quite efficient.

    For 7 MHz and especially 3.5 MHz you'd want the loading coil to be at the centre or towards the top of the antenna.

    That's less accessible but it's more efficient than base loading.

    Note though that you will need more inductance nearer the top and it becomes mechanically more difficult.

    A bit more length would be highly desirable for 3.5 MHz. VK7JJ has some ideas for a multiband vertical at http://www.perite.com/vk7jj/squidpoles.html
     
    NH7RO likes this.
  3. KB1CKT

    KB1CKT Ham Member QRZ Page

    I'm not sure how the loading coil can be 6' and your radials be at 45 degrees. Not on 80m.

    For a portable antenna I'd just assume the radials are flat on the ground, coming off however they can from the feedpoint. Now, if you can elevate them a few feet up, by using various stakes in the ground, you can get by with 3 or 4, but they need to be resonant; of course they'll be detuned by proximity to the ground. For something portable I'm not sure the effort is warranted of elevating the radials. Just like it won't be worthwhile to put down 120 30' radials (let alone 120 quarter wave long radials). I'd go with 3 or 4 radials that are cut to about the formula for quarter wave; they will be detuned by the ground but it is what it is. More will be better. If you are thinking of running 80, 40 and 20, then perhaps 3 per band, roughly quarter wave. Fair amount of work to roll out wire, but if you get the right kind of wire it should be kink free (or go cheap and expect kinking and cursing).

    You'll need a decent tripod to hold the antenna up. I was experimenting last with some 2x4's with a small let-in notch in them, that I could shove a 3/4" PVC pipe into for a mast. Didn't finish it up but it was a start. I'm not sure that a metal tripod will have that great of an impact, just keep the radiator above it. That said... everything works. I'd be more worried about the tripod holding the works up, rather than any electrical interaction.

    For 80' operation I'd use at least one MFJ-1600T, maybe even two--that might put the loading coil up too high to adjust, but it's the radiator below the loading coil that does the radiating. Use as much as possible, up to a quarter wave long (ha!). Ideally another 4' mast above the coil and then a capacitance hat; but at this point it's going to be hairy to keep this standing. Not without a heavy base or tacking to the ground somehow. Which may take the portable aspect out. On the good side, if this is all made with 3/8x24 fittings, you can always play to your hearts content. Just add or subtract components as you make them. There may be value in building something, and then later improving it--the pursuit of perfection being the enemy of the good enough and making contacts.

    Not sure where to buy a capacitance hat with appropriate 3/8x24 fittings (male/female so it can be screwed in and out), but this should be something easily made. Heck, given the size of this antenna, the capacitance had could be made out of guy wires connecting to the 4' section above the antenna--come off with some wires, transition to guy rope, stake to the ground.

    An automatic tuner like an LDG-RT100 or others may not have the capability of wide range tuning (let alone high voltage as required for a short whip) but it may be useful to pull the radiator for faster QSY. As in, use an analyzer to find best tap for center of band, and then let a remote tuner do the fine work of matching.

    I've been toying with something of this sort. Start with an MFJ-1654, or at least the MFJ-67, to get the loading coil with 3/8x24 fittings. MFJ-1600T's for 4' sections. Just haven't gotten past the thinking stage yet though.
     
  4. AI3V

    AI3V Ham Member QRZ Page

    Your profile says you live in Georgia.

    They got trees down there.

    For as much effort and money you are going to spend, I believe you would be much better off installing a simple "inverted vee" half wavelength, center fed dipole.

    Make it a "yo-yo dipole" for qsy.

    Rege

    P.S. you won't need to spend money on a "antenna analyzer" with the yo-yo, your rigs built in vswr meter will be all you need.
     
  5. AF7ON

    AF7ON Ham Member QRZ Page

    Trees tend not to be very portable, however! Park rangers also may take exception to you hanging things over their trees.

    Also end-fed verticals are a bit of a nuisance if you have to deploy radials.

    I'd go for more height and recommend using a center-fed vertical supported by a telescoping fiberglass pole.

    Mike
     
    NH7RO and WB5YUZ like this.
  6. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Welcome to the hobby!

    The antenna is the most critical component of any amateur radio installation. Many happy hours can be spent working DX and ragchewing with even mediocre antennas, but poor antennas have brought a frustrating pre-mature end to many an amateur radio career.

    Basically, what you are suggesting (four non-resonant wires to cover all bands 80-10m with no tuner) is not practical in that it is very likely to make a poor antenna.

    Most ground planes use either 16-32 non-resonant radials or 3-4 resonant ones for each band. A few non-resonant radials are likely to increase return losses to the point where they would become objectionable. This is perhaps the biggest obstacle to using a vertical as a portable antenna; a good radial field is large and does take a little time to set up. This is why so many people use dipoles suspended as inverted "Vs" from 33' or so fishing poles as portable antennas. Good performance on 20m and down in wavelength (14 MHz and up in frequency) and fair performance on 40m. 80m operation would be mostly limited to regional and local work at that height.

    For a portable vertical, 40m is accepted by many as a practical limit. Even with loading and tuners, 80m antennas shorter than 33' can be problematic. However, a 40m vertical can be made to work on 80m as the vertical part of an inverted "L" simply by adding a run of wire to the top.

    W5DXP had good results with a 22' vertical and four 22' 45 degree radials fed by an SGC autotuner. My understanding is that the autotuner "sees" the radiating element and the radials as a center-fed dipole and tunes the radials as well as the radiated element. http://www.w5dxp.com/vert4010/vert4010.htm

    Charles, KC8VWM, is a master of building efficient antennas from inexpensive, common components. His design for a fishing rod vertical that will work 30-10m (and 40m when configured as an inverted "L") is here:

    https://forums.qrz.com/index.php?threads/fishing-rod-vertical.569241/
     
  7. KB1CKT

    KB1CKT Ham Member QRZ Page

    I guess the question becomes, how much time is allowed for antenna setup? Something can be portable yet take an hour to set up (witness many Field Day expeditions).

    Re-reading the OP: wild thought. If you have a car, can you use the car? Usually we think of getting a screwdriver or a magmount on the car. But there are metal plates that you can park a wheel onto; and said plate has welded to it a short mast or the like. Which can then take a taller mast. Which then can be used to mount whatever antenna you come up with. Thus making it independent of trees and other supports.
     
  8. NH7RO

    NH7RO Ham Member QRZ Page

    Rudy Severns, N6LF perhaps one of the greatest HF vertical gurus around determined that only four radials per band 0.15 to 0.40 wave length elevated 4 feet above ground equates to 120 ground-mounted radials. That's quite a wire savings as well as much time and effort spent to be saved going this route, too.

    With such a wide ranging acceptable length for these "resonant" radials it makes me wonder about all the statements about tuning them in the first place. Anyway, there's a huge advantage in elevating your vertical 6 feet or so and running the radials you do end up using out to several lightweight fiberglass driveway markers that usually come in 4-foot lengths (the orange ones at Wal-Mart/Home Depot are the ones I'm referring to).

    YUZ: Since I was not able to respond to your post the other day in a thread that got closed suddenly; yes, I am back in a manner of speaking. Our place appears to be OK although the woods out back now look like a dead forest on the moon after Harvey swept and vacuumed his way through town. We are heading home on Monday to see if the inside got water damage and begin the cleanup where necessary. Pretty sure my triband vertical with elevated radials got blown into the next county so will have at least one antenna to rebuild...

    73, Jeff
     
    WB5YUZ likes this.
  9. K4SAV

    K4SAV Ham Member QRZ Page

    The antenna you are contemplating will operate a lot like a mobile antenna. The gain will be low, especially on the low bands, but you will still be able to make contacts with it, just like you can with a mobile antenna.

    The SWR may be a problem, especially with only a few elevated radials. The feedpoint impedance will likely be too low. Many mobile antennas have a shunt coil that goes across the coax at the feedpoint to compensate for this. Your antenna won't have that, unless you add it. Without that coil, I think you will be lucky to get an SWR of something close to 3 to 1 on 80 and 40 and that could be a problem for a rig with no tuner. However it is possible by juggling the radial length to get a low SWR on one of these bands. I don't know if it is possible to get a low SWR on several bands by using radials of various lengths. That would require some analysis (or a lot of experimentation).

    If you have just a few radials and they start at 6 feet and then droop to the ground (or happen to be on the ground), that will likely improve the SWR but will decrease the gain because of increased ground loss. Length of the radials will effect gain, SWR, and resonant frequency.

    Without a choke on the coax at the feedpoint, the coax could look like the only radial on some bands, depending on its length. If the coax is lying on the ground, that will lower the gain and improve the SWR.

    A car can provide a reasonable ground plane for the antenna, just like it does for a mobile antenna. Location of the antenna on the car can change the shape of the gain pattern. Max gain will be in the direction where there is more car metal.

    Jerry, K4SAV
     
  10. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Very glad to hear it. Be careful when you go back.
     

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