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First dipole - 20m - 300 foot tower - Bristol Bay Alaska

Discussion in 'Amateur Radio Antennas' started by radiofreq10, Jun 26, 2011.

  1. radiofreq10

    radiofreq10 Member

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    Hello,

    I am having trouble picking up any dx stations, or any stations at all. I am located in Naknek, Alaska and am attempting to operate on 20 meters. I am working at an FM radio station where I have setup the ham radio. I am running an old Kenwood 520s tube style transceiver that is in great condition.



    The station operates on 100.9Mhz FM at 1000 watts on a 331 foot tower. I have cut a 1/2 wave dipole and installed it as a vertical vee at 50 feet with 100-120 degrees angle of separation. The antenna is made using #14 AWG shielded solid copper wire. I am running about 150 feet of RG-8 coax. The antenna is fed using a 1:1 PVC style balun.

    I have cut several antennas and am having trouble getting an swr lower than 1:3. I also cannot hear any stations at all on any band. Today is ARRL Field Day and you would think I would be able to hear someone. Even though I am probably hundreds of miles away from the nearest 20 meter station I should be able to pick something up.

    My notepad of the layout of the tower, guy wires, antenna (red), and station.
    [​IMG]

    Me installing the wire antenna at 50 ft.
    [​IMG]

    Any thoughts? I am new to HF and need some help.
    Thanks,
    Ben
     
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    Last edited: Jun 26, 2011
  2. Robb

    Robb Yup

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    What's wrong with 1.3 SWR?
    Certainly isn't going to be the cause of no reception. Is it a 'balun' or an RF choke that you made? Sure would be a lot easier for you to have an antenna analyzer; but that isn't the case here. An antenna tuner too. With all of that height to work with, have you considered of cutting a dipole for 80m? Tried to talk to any locals on 20m?
     
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  3. radiofreq10

    radiofreq10 Member

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    Sorry I wrote that wrong. A 3.0 SWR. Its a balun i purchased. An MFJ-918 1:1 current balun. MFJ-918, Balun 1:1, 1.8-30MHZ It was recommended to me by a ham friend in Minneapolis. I havent been able to talk to any locals. I dont know of any other hams near me. Maybe in Anchorage, but I havent heard a whisper.
     
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  4. W5LZ

    W5LZ Crotchety Old Bastard

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    I'm very surprised you aren't hearing something.
    A 20 meter dipole should be around 32 - 33 feet long. With an angle of something like 120 - 160 degrees between the two 'legs' I would think you should be seeing better than a 3:1 SWR.
    How close is that antenna to any guy lines? That's sort of a 'reach', but the first thing that comes to mind. (I'm assuming that the horizontal appearing lines just below the guy on the tower are guys?)
    Another possibility is that balun. Just for grins, by-pass it and feed the dipole directly. I honestly don't think there's a problem with the thing, but it just really isn't needed. By-passing it would at least rule out it being a problem. And while you're "grinning", hows the thing oriented, east/west or north/south? Either way you should be hearing something.
    Interesting!
    - 'Doc
     
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  5. radiofreq10

    radiofreq10 Member

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    I cut my dipole to 32.75 ft = 2x 16'5" legs. I did notice that the SWR lowers as I raise the frequency, I imagine it would be close to resonance around 16Mhz, meaning my antenna is short.

    If you look at the photo, 50 ft is right where the red transition to the white, the antenna is hung there. The guy wires are 4 ft below the antenna. If you look at the drawing, the antenna stretches the line from 43.5 degrees (NE) to 208.5 degrees (SW). This gives the antenna gain towards 133.5 degrees. I have a friend in Minneapolis I would like to hit, so I oriented the antenna that direction (SE).

    Ill try bypassing the balun tomorrow. I did notice that using an ohm meter, the balun appears to short circuit across the two antenna leads. Which also looks like a short circuit across the feed line. But I read that at DC that is normal, but at ac acts as an impedance matcher. I also noticed that while hooking the feed line to the radio, when I plugged in just the center lead of the pl-259 plug I had high receiver gain, but when I plugged the rest of it in, including the ground, the receiver got much quieter (but still rather noisy). Any ideas?
     
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  6. Robb

    Robb Yup

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    At any point, does the SWR get to be reasonable - say 1.2 -1.5 - regardless of freq?

    To be on the safe side and for troubleshooting purposes, would it be possible for you to re-hang your dipole either 12 ft below or above the guy wires? Especially near the ends. None of the guy wires are parallel in any way to your dipole - right?

    If it is set up as an inverted "V"; then it should be less directional. If the angle is close to 90 degrees; it should be fairly omni-directional.

    That balun is really a choke. The product description says it is just a piece of coax inside with 30 ferrite beads on it. It is not a transformer at all; just filtering RF off of the feed line. It acts more like a one-way valve and should be completely neutral otherwise.
     
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    Last edited: Jun 26, 2011
  7. doctor

    doctor Supporting Member

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    ANT

    I would cut your antenna for 40 meters, then it would wrk 10-40, 80 meters was not good when I lived in ALASKA, also make your antenna as an inv v and to talk to Minneapolis make it directional toward them. Also make sure your angle is at least 90 degrees. Disconnect the balun and just use a center insulator<I use w8amz center insulator>.
    If you still don't hear much for experimenting for a few just take 50 feet of wire and solder on to that <coax center conductor> and see if you hear people on the band...I bet it is the balun, or the support cables causing interferance...

    Keep us posted.

    DOCTOR/795

    P.S. I lived on ADAK ISLAND for 15 months..a paradise in Alaska
     
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  8. 148 Alaska

    148 Alaska Member

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    the bands have been pretty dead for us up here in the northern region.....I live in Anchorage
     
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  9. towerdog

    towerdog one-niner-seven

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    Could be the radio? SWR is not as important on receive at transmit. I had a dipole break in half and it still RX on the amateur bands. Could it also be RFI from the FM station? If it were me I would want the wire as far off the tower as possible, at least 6 or 8 feet, suspended from 2-3/8" pipes attached to 2 legs across the face of the tower with ubolts and crossover plates.
     
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  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    I was wondering the same thing about both. Make sure the RF Gain is turned up and peak the DRIVER control as it tunes the receiver frontend as well as the driver stage. As for desensing from the FM transmitter, it could be happening but I doubt it and in any event if it is then moving the antenna out from the tower won't help any as the tower is not hot but the antenna 280 feet above it is. I know a few hams that are station engineers and actually live at their transmitter sites and have no problems with desensing from either AM or FM. One guy lives at a 10 Kw AM site and has no problems working 80m and up and only a little splatter on 160m and tat with no extra filtering.
     
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  11. radiofreq10

    radiofreq10 Member

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    I dont know. I cant tune outside the band with this radio. I should mention, Ive also got an Icom 706 here which Ive also tested this antenna with. I cant hear anything on the 706 either.

    I can try that. The guy wires are not parallel. We have had some high winds and rain yesterday, today, and tomorrow. Gusts up to 35knots. So I wont climb the tower till maybe Wednesday.

    What has been working for you? Could we try a contact sometime?

    I have also tried receive on the Icom 706, and nothing on that radio either. Ive also powered down the FM transmitter to see if I could hear anything and that didnt make a difference. So I dont think Im getting any RFI from the FM station. I should mention there is also an 800 MHZ cell phone antenna mounted at 320 feet as well, 3 poles. With all the feed lines running up the tower, I ran my feedline along one of the legs that has an unused feedline.

    Ive been following the tuning procedures in the manual, and I have no signal to peak with the driver... I usually cant find anything over S1. Ive tried random length wires for rx and havent heard anything on those either.

    Also, as a note, I had this radio checked out at a ham shop in Minneapolis before I brought it up here. They checked her out as good on RX and TX.

    I think what I am going to try next, is to cut another antenna at 20m, and hang it without the balun. Weather permitting.
     
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  12. radiofreq10

    radiofreq10 Member

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    We had clear skys yesterday so I had a chance to get some photos of the radio station from the air. I thought I would share with you. You can clearly see the tower and the station building. Also notice the smaller building running feed lines to the tower, thats the cell phone transmitter building. You can also see a smaller tower farther back, thats an old tv tower that is no longer operational. There are no signals from that tower. Again, the antenna is mounted at the bottom of the first white stripe.
    [​IMG]
     
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  13. 148 Alaska

    148 Alaska Member

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    well about 4 in the morning there has been a few stations on 20m I leave the house at 520 and some times by then it is all gone...pretty poor conditions lately , I do check in on the motley net on 3.933 and even the 75m band has been poor...
    I use the HARRP monitor to see what bands are open for us...
    Spectrum Monitor Waterfall Chart
    kind of a cool tool to have
    I run a 270' loop and a imax 2000 and a couple of beams....oh and I have a g5rv up as well, you can have all the antennas you want but if the band is dead the band is dead.....and its been dead....
     
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  14. radiofreq10

    radiofreq10 Member

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    Wow, ok, well that makes sense. Ill have to listen at 4am and see if I can hear anything. Thanks for the link.
     
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  15. Moleculo

    Moleculo Administrator Staff Member

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    There is a difference between resonance and low SWR. The G5RV is nearly resonant on several bands, with 20 meters being the best. Take a look at W8JI's resonance figures on the G5RV. His commentary and analysis of this antenna is also interesting. You can also see from the figures that he documents that the SWR is not so unacceptable that most autotuners won't have any problems with it on most bands. The bands where it has the worst loss (not including 160M) is 30m and 10m. 17m isn't great, either. http://www.w8ji.com/g5rv_facts.htm
     
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: 20m, alaska, tower

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