Getting into amateur radio

Discussion in 'Survival Communications' started by Huntinbull, Jan 30, 2012.


  1. Tikka

    Tikka Monkey+++

    My last towers set in 6 yards of re-barred concrete. Usually the antenna is more at risk than the tower.

    I've had a variety of HF antennas; Tri-bander +WARC, bandpass log periodic yagi, and Quads. The Quad is my favorite; the bandpass LPY was one feed line instant satisfaction.

    The story of the Quad is quite interesting also.
    [Towertalk] The Quad antenna was developed by HCJB

    Wire antennas work well; some offer low band gain and low angle of radiation. The pitch of a roof is a natural inverted V.

    These are great getting an antenna up a tree.
    http://www.wcerc.org/Projects/images/slingshot-antenna-helper-01.gif

    I use a sling shot and a fishing pole. :D
     
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  2. Idahoser

    Idahoser Monkey+++ Founding Member

    too much going on here. You are wasting your time trying to make a long dipole work on shorter bands and using coax. Ladder line, twinlead, or open wire line has 'practically' zero loss even at very high SWR, but coax has very HIGH loss when not matched.
    So put up your wire, and feed with coax, and use it only on 40. I think it may resonate on 15 also... something about odd harmonics.

    I think what you're contemplating is not a dipole if you feed it at the end, and I don't think coax will work even for the resonant band fed at the end without some kind of matching network. Again I'm too new to be fluent but I do think it's not that simple.

    Wire is cheap. set up a feed line to the outside and try different antennas. Something will work well for you.

    Bringing ladder line down the roof from the center is common, I think. You're supposed to twist balanced line and that would keep it from laying flat at least, even if you didn't have it elevated. I'm not sure that's okay, but I have read of it being done. It just has to be kept several times the space between the connectors away from metal. I would suppose it could also be bad touching a wet roof.
     
  3. ghrit

    ghrit Bad company Administrator Founding Member

    Wasn't thinking dipole to start with, but I need to rethink the whole scheme anyway since I can't make 66 feet on the ridge line. Doable best along the ridge is about 50 feet. So far as tuning/matching goes, well, that will have to be done anyway. Ladder leads just won't make it without some supports on the roof I'm unwilling to do, too many possible ways for a leak to happen. Back to the drawing board ---. (Twin lead is possible, even if snowed under. I think.)
     
  4. Tikka

    Tikka Monkey+++

    Ladder line is ~420 ohms and a dipole at 1/4 wave above ground is ~70 ohms.

    You want to match the impedance of the antenna and the feed line as closely as possible.

    If you want to feed it with a form of ladder line; use 75 ohm TV twin lead to match the antenna.
    That should get you a little less than 1.1 on swr. Antennas in free space are easy; in real life there are a lot of factors.
     
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  5. Seacowboys

    Seacowboys Senior Member Founding Member

    I just set an 80 meter Dipole in the tree tops. I used a fishing sinker attached to a rod and reel and a slingshot to shoot a messenger line into forks of trees and passed a para-cord, then the line that will support my antenna. I also placed a screen-door spring at each attachment point for a shock absorber when the wind get a bit brisk and trees don't tend to sway synchronized. No tree climbing involved, Ghrit.
     
  6. Idahoser

    Idahoser Monkey+++ Founding Member

    a dipole connected to ladder line and run to either a tuner capable of tuning balanced line; or a balun with a short coax jumper to the tuner, does not need to be matched at the antenna. What freq would you match it for? It's purpose in life is to be used on mostly non-resonant freqs and the impedance would be all over the place. It simply isn't necessary when using balanced line on a balanced antenna; the loss is insignificant even when severely mismatched.

    reminder- this is from reading, I have no experience yet.
     
  7. Tikka

    Tikka Monkey+++

    I was a teaching VE but that was 23 years ago. So, it has been a very long time. LOL

    "The matched method for coupling a line to an antenna consists is matching perfectly the antenna impedance to the characteristic impedance of the line. This method will gives a very low SWR, below 1.5:1, less than 1/20th of the input power is reflected, and the input impedance will be purely resistive, regardless the line length. In other terms the line will be "flat" or at least its lost by radiation are considered as negligible."
    All about Transmission lines

    I was a DX'er and the FCC created all DX'ers equal except if my antenna radiates more of my RF than yours; simply stated means more watts hit the antenna, more bandwidth with a low SWR.

    ANTENNA TUNER MATCHING PROBLEMS AND SUGGESTED FEEDLINE LENGTHS

    It can get a lot more techie when you don't consider from the radio to the tip of the antenna as one circuit. Antennas are both an art and a science.

    I hoped that helped. ;)
     
  8. ghrit

    ghrit Bad company Administrator Founding Member

    Had another look at the land this afternoon. I have a pair of trees a bit over 100' apart that might do, orienting the wire at about 300 degrees magnetic. At least I can get a nominal 66 feet of wire around 25 feet +/- in the air for short money, using paracord to hang a counter weight on one end (and maybe to support the wire as well.) These are thin, whippy trees in the range of 50 foot high that do a LOT of moving in wind, the screen door spring won't work well for very long. If I set the wire in the right segment of that 100 or so feet, I can use a ladder or preferably twin lead to bring the feed to the house (about 30 feet horizontally and maybe ten feet above the propane pig) off the center of the "66" and pass it thru a window. I guess there has to be a transition from twin lead to coax somewhere convenient, maybe right at the window outside so it can be reached for manual tuning of whatever has to be there. May also need a lightning arrestor too, since we get a lot of that up here, so just outside the window strikes me as a good spot for all the goodies.

    Was also looking at commercially available antennas. Price scared me off of Hi-Q, which I was thinking might do well for base and mobile. {Shudder} Us fixed income folks have to watch out a bit for "investing" in things that use time.

    Idahoser - Still thinking 40 meter as the main operating band. Any other resonant bands would be nice to have. What isn't clear in my MT head is if that is a good choice. Given the lay of the land and what's around to work with, that's the longest wavelength easily reached from here.

    Tikka - Back in the day, I was able to achieve SWRs of less than 1.1 on all the antennas that I had in service on CB, on all channels. It was "common knowledge" that a SWR approaching 2 was hazardous to the finals. Rode that horse, and tuned things to the best I could get. Now, I don't know if xmitters these days are capable of handling SWRs as high as I've seen mentioned in the theory books without risking the transceivers, but seems like the sets have to be more tolerant of mismatch.
     
  9. Idahoser

    Idahoser Monkey+++ Founding Member

    The $4 Special
    "But beware: Marconi spins in his grave everytime a ham buys an aerial instead of building it."
     
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  10. BTPost

    BTPost Stumpy Old Fart Snow Monkey Moderator

    Just about ANY wire antenna will work... Some just work better, than others.... The Idahoser linked one, will work just fine. 40 meters is a great Band for the evenings, and long distance Comms, most nights. Same with 80 meters. During the day 20 meters will usually open, and with a tuner, that antenna will load just fine, and no issues, clear up to 10 meters. ..... YMMV....

    PS with a balanced antenna, Ground is only needed for Lightning Protection, and not for the RF Radiation from the antenna.
     
  11. Tikka

    Tikka Monkey+++

    I enjoy antennas, so I build them from wire because it is cheap fun. Play with them for a few months or more. Anyhow for me it is fun, lol.
    When you buy an antenna; you assemble it and fine tune it. When you build an antenna, you do all the "math" and tuning. Direct match gets you the "most" out of an antenna.
    Twin lead is balanced line and your radio is unbalanced. Although you don't need one; I personally use a balun.

    Balun - Wikipedia, the free encyclopedia

    More technical Baluns in theory

    I prefer current baluns and the link is a source or you can build current baluns.

    A high SWR produces heat. Radios with transistor finals do not tolerate heat for long. My rig has a built in tuner which is nice for mobile/field day etc.
    My old TS530-SP has tube finals 2x 6146B which are much more forgiving than transistor rigs.
    Tube final rigs have a load and plate control which matches the network load and plate tuning of the finals to the antenna. Sort of a built in tuner tuning the output to the load. Drive tunes the driver tube and some other things.

    www.eham.net/data/classifieds/images/351754.jpg

    If the wire runs 330 to 150 that is the nulls; peak rx/tx 60 and 240; however it will cover a lot more. My first DX was Europe, Africa, SA with a windom 20' up and part of the vertical section ran parallel to the ground.. (Think of a Novice building first antenna.... LOL)
    :D
     
  12. Tikka

    Tikka Monkey+++

    When a dipole is horizontal the impedance is ~70. As it's ends are closer to the ground an inverted V's impedance is closer to 50.

    The balun would connect the coax to the antenna.
     
  13. ghrit

    ghrit Bad company Administrator Founding Member

    So comes the questions.
    -Do Tx/Rx units care what the antenna impedance is at the connection to the unit?
    -If a wire dipole has an impedance of ~70 ohms, is a 75 ohm twin lead "close enuf?"
    In other words, can I use a 75 ohm twin lead to feed the antenna directly from the radio?
     
  14. BTPost

    BTPost Stumpy Old Fart Snow Monkey Moderator

    Rx really doesn't care much about Antenna Impedance, as the Power Levels are so low, the I2R losses are insignificant. For Tx, the difference of 5 Ohms is not significant in Power Loss when compared to the Impedance Difference due to other Factors, like the Real Impedance of the Actual Antenna at the Transmitting Frequency. Most Non-Tube Transmitters have a Power Foldback Circuit that drops the Drive Power to the Final Amp, to keep the Final Transistors from Burning OUT. The better the Match of Final Amp to Actual Real Antenna Impedance, the less Power goes into Heat, the more Power goes out the antenna, and the higher the Drive to the Final Amp until it reaches saturation, or Over-Temp, which then Backs down the Drive.
     
  15. Tikka

    Tikka Monkey+++

    An inverted Vee can be fed with 50 coax. I would recommend using a 1:1 balun at the antenna so both elements of the antenna will radiate alternatively. Baluns can also stop common mode currents (RF) on the feed line.
     
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  16. manderson2228

    manderson2228 Monkey++

    There is a website that just started up Prepared ham. Survival ham radio ops the entire site is about ham radio for preparedness, they help getting people licensed and on the air. You guys should check it out if your are into comms. They are building a group of a pretty experienced ops, and getting ready to setup an on air net to practice the skills once you get licensed.
     
  17. Silversnake

    Silversnake Silverback

    Any downloadable study guides for technician and general? I just contacted the local club and have a couple weeks before they test again. If not then, it will be 6 weeks out. Maybe longer based on how much material I have to learn.
     
  18. BTPost

    BTPost Stumpy Old Fart Snow Monkey Moderator

    SS... there are some sites... I would ask over on Prepared Ham... They are a good bunch and will lead you right and CHEER YOU ON... Tech shouldn't be to hard, and General is doable...
     
  19. ghrit

    ghrit Bad company Administrator Founding Member

    "They say" tech will eat up about 20 hours, and general another 30 for proper preparation. Might be good numbers to shoot for, but I took longer for the tech, partly due to taking the class offered by the local club.
    As BT says, preparedham.com has a good bunch of guys that know things. Read some of the posts, there are specific recommendations for study guides on line and downloadable for a fee.

    They will encourage (read that as PUSH) you to take both tech and general tests at the same time. Can't recommend that approach because I didn't try it.
     
  20. Idahoser

    Idahoser Monkey+++ Founding Member

    Here's some links that should get you going. There are books you can buy but I wouldn't recommend any of them over the free stuff.
    AA9PW FCC Exam Practice » Amateur Radio Exam Practice
    No-Nonsense Study Guides - KB6NU's Ham Radio Blog
    HamExam.org: Free Amateur Radio Practice Tests with Flash Cards
    Practice Amateur Radio Exams by QRZ.COM
    eHam.net Ham Radio Practice Exams

    You should attempt General while you're there. Much of the prep for Tech is also applicable. Doesn't hurt, nobody will know if you don't pass it, no harm in trying.

    Take practice tests by the hundreds and if you're doing 90% on them after a while, you'll pass the test. The questions and answers that will be on the test are the exact same ones you can get from the internet. The only thing I remember is I had done so many practice tests, I was remembering which answer letter A) B) C) D) was correct, but on the real test they were not in the same order.

    Take practice tests even though you don't have a clue as to the answer. Just guess. The practice test will tell you which ones are right and if they're wrong, it'll tell you which answer is correct.

    I did a combination of the methods. I tried using the study guides that explain the answer, the ones that show only the correct answer, the ones the phrase the answer in the form of a sentence... I think for my brain it was most beneficial to answer tests that I didn't understand. I did get to remember which answer was right, even if I didn't know what it meant.

    That, combined with learning the easy formulas for wavelength in meters/antenna in feet, wavelength to frequency, etc. Like Ohm's Law, you can draw yourself a little cheat sheet on the scratch paper. I'm not talking about cheating, you aren't bringing this in on paper, you take the scratch paper and before you start the test, draw the little helpers. They make it easy to remember what to calculate. Put your thumb over the value you need, and it tells you what to do with the values you have. Picture these with a circle around them, or I've seen some people use a triangle. For example if you have Volts and Ohms in this drawing,

    E
    ------ where E=Potential in Volts, I=Current in Amps, R is Resistance in Ohms
    I | R

    cover the Amps and it shows Volts over Ohms, which is a division, Volts divided by Ohms to get Amps.
    If you have Amps and Resistance, cover the E, and now you can see you multiply I times R.

    Same idea with these:

    300
    -------- where the constant 300= the speed of light in km/sec, f=Frequency in MHz,
    f | m and m=wavelength in meters.

    468
    ------- 468 is a commonly used conversion factor
    f | ft f=frequency in MHz, ft is length in feet of a halfwave dipole

    I know I've seen the stupid thing somewhere but I can't find it now, so I drew it.
    It was simpler for me to memorize this, to be able to draw it on the scratch paper, than to actually learn that stuff at the beginning.
    OhmsLaw.

    Of course you want to learn what you need to be a proficient operator, I just don't see the need to do that first.
     
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