discone antenna for HF?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K6ELV, Jun 13, 2012.

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  1. K6ELV

    K6ELV Ham Member QRZ Page

    I noticed that there are discone antenna's which cover from 50 Mhz - 1.2 Ghz with a low SWR and not require any tuning. I was wondering if it is possible to make a much larger discone that will be able to cover most if not all the HF band and not require tuning like the one for VHF/UHF. It seems like if you made a discone much larger it would work on most of the HF band since discones are wideband antenna's. I was thinking that it would be awesome if I could have one for HF since it would probably be able to cover most of the bands without a tuner, but I have not seen any discone's that are for HF. Has anyone tried this? Would it be possible to make a larger discone that would work on at least the higher HF bands without a tuner?
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    There are HF discones installed all over the place, mostly at military installations (or government-funded scientific research locations).

    First, don't be misled by the "50 MHz to 1.2 GHz" stuff. It's all nonsense. Those antennas are discones for 150 MHz through 1.2 GHz (3 octaves coverage). They are not discones below the 2m band; they "load up" on 50 MHz by having a 6m coil-loaded whip screwed into the top, and that is NOT part of the discone. On six meters, they're just a vertical whip over a mediocre ground plane and have substantial "negative gain." On 2m through 23cm, they're really a discone.

    An HF discone for 3.5 through 30 MHz (also about three octaves) is absolutely possible and there are hundreds, maybe thousands of them out there. They take up a LOT of space! Picture the VHF discone you discussed, but exactly 43 times larger in all dimensions. That's what it would take to cover the HF bands (not including 160 meters).

    It needs to be about 86 feet tall, suspended well above earth, so the "top" of the discone (the "disk" part) needs to be about 120 feet above ground. It also needs to be about 86 feet "wide." The military ones I've seen use a 120' tower as the primary supporting structure, with hundreds of heavy gauge wires suspended from that to make the disk and the cone.

    If you have the property and money, go for it! Plenty of HF discone designs on the web.
     
  3. N3JBH

    N3JBH Ham Member QRZ Page

    Ya beat me to it Steve but i was going say same thing i seen them when i was in the Army
     
  4. K0SPN

    K0SPN Ham Member QRZ Page

    There is one at the Titan Missile museum in Arizona.
    You can certainly make one but it would be rather large.

    Search Google for HF discone.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Ditto here. They had one at Ft. Monmouth many years ago, and I think there was one at Ft. Gordon back in the 70s also. I have no idea if they remain intact after all this time.
     
  6. K6ABZ

    K6ABZ Ham Member QRZ Page

    It's possible. It's even been done. The problem is the size. A discone has to have a diameter of somewhere around 1/4 wavelength, with the bottom of the cone a little wider than the horizontal radiators. In other words, a discone that covers 80 meters and up would have to be 24 meters across at the bottom and 17 meters across at the top. Supporting the horizontal radiators at the top would be fun; it could be done, but it would require a lot of work to set up.

    Back when I first got in to amateur radio, I also thought about setting up an HF discone. When I was researching them, I came on this site: http://jeremiah.oeltjen.us/discone.html

    Here's a little light reading, as well: http://en.wikipedia.org/wiki/Discone_antenna
     
  7. KO6WB

    KO6WB Premium Subscriber QRZ Page

    The ARRL Antenna Book has the construction details on how to make a discone antenna for HF. It will be effective but not as good as a simple dipole. The difference would be hard to see. The amount of wire required is substantial. The top portion is usually made just a little smaller then the ideal dimensions and that helps make it easier to build. It takes up a lot of room and like the other guys have said you can usually spot one on a military base. I was in the USAF and there was the discone and a really large LPDA. They needed the versitility to move frequencies rapidly and it's a pain to have to tune the antenna.
    For general coverage the discone is okay but not super. My feeling about it is that it takes up a lot of real estate without giving you any gain over a simpler smaller antenna.
    Hope this helps
    73
    Gary
     
  8. 4L4AGU

    4L4AGU Ham Member QRZ Page

    HF discone does not needs neceserrly to be the "disc" shape. That is done just for uniform directivity. The main part is the "cone" which provides wideband coverage. So a simple HF discone can be made using two tall supports, one wire hang between them. to the center of that line the feedpoint is attached (center of coax) and two wires are going down just like Inv V antenna and are attached to coax braid.

    But you should remember, discone antenna has no gain. So final effeciency will be low. So, as it was mentioned before, if you got high enough supports, just hang G5RV or something similar, which will give you better results.
     
  9. N1KPW

    N1KPW Ham Member QRZ Page

    I have a Swedish Military surplus man-pack portable discone that can be configured for <30mhz or >30mhz by altering the lengths of the elements. It came with a 35ft sectional mast and I've mostly only ever used the mast to support other antennas, I'll have to set it up and give it a shot this weekend, see how it plays. The name on the carry bag says :Hogantenn 1 M1921-101011" and the advertisement is archived at : http://www.sportsmansguide.com/net/cb/cb.aspx?a=170520

    I set it all up once to test it out with FT897 when I first got it, but I was still just a Tech then and it was a bear to put up with 2 people, so I've only used the mast for other antennas, a picture or two of which are on my QRZ page. I'm currently working on a hinged base to slide into the Reese Hitch on a 'new to me' vehicle, should make it alot easier to set up that way, we'll see. I don't remember exactly what I paid for it back in '06, but I do remember it was a steal compared to what other companies were getting for comparable portable fiberglass or aluminum masts at the time. I did find a reference via google search to my original posting in the yahoo 897 group in regards to my first testing this antenna :

    "I just got back from the local state forest where there is a
    nice wide open space to set this antenna up to test it out.
    Tunes/transmits good up to full output of 897D on 6m, 2m, & 440. Did
    a good job of "repeater hopping" on all three bands. There wasn't
    any good simplex activity today to try SSB on those bands. The set
    up is a seriously wide-band discone that can be configured
    for "above" or below 38 MHz. I only set it up with the above 38 MHz
    configuration, but it worked fine there. I did not transmit on HF,
    as I have no privileges there, but was able to copy a QSO between
    a "K9_ _ _" station and another in Guatemala on 40 m. I was also
    able to copy WWV in Colorado on all bands. A quick scan of the
    broadcast shortwave bands brought stations from all over the world.
    I do not own an analyzer, so I cant say for sure exactly
    where this thing is resonant, but it seems to work real well with
    the 897. I need to mention that this is not a good set up for
    Backpack Mobile use or real short term use. It is difficult to get
    the mast set up at its full height and weighs about 30 pounds in
    it's pack. With that said, it does seem that it would be a good
    Field Day, EmComm, JOTA or just a long weekend camping use where
    there would be 2 or more people available to assist with the set up."
     
  10. K7VZ

    K7VZ XML Subscriber QRZ Page

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