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27.205 Mhz and 462.5 Mhz perfect odd (17x) multiples

Discussion in 'General Technical Questions and Answers' started by Pushraft, Nov 8, 2008.

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  1. Pushraft

    Pushraft Banned

    I have a cophase harness that I made back in my CB days. Since 27.205 Mhz is the middle of the 27 Mhz CB, I guess that is what I had it cut for. I just noticed that both the shared FRS/GMRS and some GMRS channels are almost exactly 17 times the frequency of 27.205 Mhz. That means that a 1/4WL phasing line on 27.205 Mhz is still good (usable) for 462.5 Mhz as a 17/4 WL phasing line and probably even all of the GMRS & FRS freqs even as high as 467.7 Mhz. That is really convenient for me because I still use both of those bands and like some directivity. I find that very convenient and just wanted to share that info in case anyone else in interested in playing around with cophasing both bands like me.

    I can get the optimal spacing (2/3WL) for the UHF setup but unfortunately for HF (27 Mhz), I can only get about 1/4 WL spacing on my vehicle although I still get the larger aperture and spacial diversity plus the -3dB quieting off the sides.

    Perhaps I should use a "90-90" setup for 27 Mhz using a delay line on the leading antenna for that nice wide cardioid azimuthal shape (similar to a 3 element Yagi-Uda beam) with 3dB additional gain in the favored direction.
  2. W9MAV

    W9MAV Ham Member QRZ Page

  3. WA9CWX

    WA9CWX Ham Member QRZ Page

    Just THINK of what you can do with phasing lines made of 1.5" hardline for 160 meters......:D

    (ouch) :mad:
  4. AG3Y

    AG3Y Guest

    Pushraft, the reason your idea is not practical is because of the losses you would incur due to the excessive length of the cable. You said it yourself, when you quoted "17/4 WL". Have you checked out the transmission line losses for that cable, as expressed in "dB loss per 100 feet of cable", which is a specification given for just about every reputable brand and type of cable.

    Why would you want to gain a couple of dB through a phased array, if the hardware used to create that array would have so much more of a loss ?

    Have you gotten your license, and actually gotten on the air, as so many of us have recommended you do ?

    73, Jim
  5. K7MH

    K7MH Ham Member QRZ Page

    "Not practical" is his other moniker.:(
  6. Pushraft

    Pushraft Banned

    the 75 ohm cable is Belden 8241 (0.66 Vf) which is RG-59/U which is 7.6dB per 100 ft loss @ 462.6 Mhz and I am using only 6 feet per leg (to each mag mount) so that is only about 1/2 dB loss per leg of the cophase harness (including the connectors). That is minor compared to the 2.5dB gain, larger aperture, and spacial diversity I am getting as well as better performance. I have only tested the UHF recently but now I am motivated to test the CB as well which should perform even better because the losses are much less on HF than on UHF. Note than 2dB (or sometimes even 1dB) can make or break intelligibility in a very weak signal. I am not talking about 20dB fading DX signals here I am talking point to point weak signal UHF.

    Also I am using all PL-259 connectors so there goes the theory that UHF connectors (PL-259 and SO-239) cannot be used for cophasing UHF freqs. Sure they work better at HF but my goal here is convenience. To switch from UHF to HF cophasing (and vice versa), I just do a few simple tasks and I got it in a few minutes. I carry the antennas with me and just switch them when I need to. I think it is fun because an omni antenna while I am parked is a waste because too much signal is going in the wrong directions.

    Now as far as the license, there is no need to pressure me and try to rush me. I have been reading my 3 antenna books (ARRL antenna book 18th edition, ARRL Vertical antenna classics (compiled by KU7G), and my Radio Shack (rat shack?) antenna book. I have also been listening in on 20 meters the past few mornings and practiced writing down callsigns which they usually say fast and with my crappy antenna (I am working on a better one), it is a challenge to get the callsign correct. I have also taken 7 or 8 practice tests for Technician class and passed all but 1 of them the first time.

    Just be patient with me I am only in my 40s so there is plenty of time for me to enjoy the hobby. I will be working on an attic antenna soon and am contemplating an outdoor 80m antenna too so stay "tuned" for an update.
  7. KJ4AUR

    KJ4AUR Ham Member QRZ Page

    Removed May 07, 2009
    Last edited: May 7, 2009
  8. KC2UGV

    KC2UGV Ham Member QRZ Page

    I guess by co-phasing, you mean the unequal y-leg cable model? (For the "cyclical polarization") or am I mistaken on this one?

    I guess Pushraft has one way of getting in the hobby, lurking the ham community, then tip-toeing in, rather than me who is rushing head-long into it :p and damned if I screw up.

    Just hope I don't get a FCC visit in the first year :p


    Knock Knock.
    Me: Hello?
    Guy:Yes, i'm with the FCC.
    Me: K.
    Guy: Here ya go. Payable by end of the month.
    Me: OH SHI-!
  9. G4ALA

    G4ALA Ham Member QRZ Page

    So What?

    Just the same way the compartive mass of a neutron is almost exactly 6xpi to the fifth power one electron mass.

    Zoop de Doop!

    So what?

  10. K7MH

    K7MH Ham Member QRZ Page

    It's always safer to just push the raft around in shallow water than hop on it and head downstream in a real adventure.
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