Antenna question

Discussion in 'Amplitude Modulation' started by N2DTS, Jul 18, 2019.

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  1. AF4K

    AF4K Ham Member QRZ Page

    So... half an s-unit at the other end!


     
  2. N2DTS

    N2DTS Ham Member QRZ Page

    Really, both the zero 5 antenna and the 80 meter dipole tuned using the drake tuna seem to work well enough to make the usual solid contacts on 40 meters.
    Others run 300 watts and I run around 200 and signal reports are both similar.
    Not to say its the best that can be done, but both are working well.

    I may try adding a 40 meter leg to the dipole but using rope to tie it to the trees instead of hanging it from the 80 meter one.
    It tends to get tangled up where it is without a lot of work to prevent it.
     
  3. N1BCG

    N1BCG Ham Member QRZ Page

    Think of it as 100 Watts of wasted energy turned to heat for every 200 Watts of RF. If you're okay with that and willing to admit it to others then go for it. This is amateur radio after all.
     
  4. N2DTS

    N2DTS Ham Member QRZ Page

    Fun with antenna's!
    Well, after having some sick tree's cut down, I put up a full size 80 meter dipole as I now had room for a full size one.
    The only tree left in the front of my property was at the kerb line and the cable TV cable and the old copper phone cable (and fios) went right
    through the same tree.
    When running over 100 watts I took out the cable TV stuff, phone, internet, on demand...
    I had to move the antenna away from the cable by making it shorter.
    I figured I had two choices, loading coils like the last 80/40 meter fan dipole, or something shorter like a G5RV.
    I know the G5RV has a bad reputation amongst real hams, but it IS only 102 feet long.
    So I put one up and fed it into my Drake mn2000 tuna.
    Its up about 45 feet, the ladder line comes down behind the house and goes into about 20 feet or RG214 modified (silver plated double braided).
    It tunes up fine on 80 meters, takes the 300 watts no problem, and people hear me.
    I cant imagine its much worse then an 80 meter dipole with loading coils in it to get about the same length (100 feet).
    Also, I can tune it up on other bands.
    And I do not have a problem bringing OWL into the basement shack.

    No RFI in the cable stuff now.
    On 40 meters, the G5RV works a bit better sometimes then the zero 5 40 foot ground plane mounted on the roof.
    Tim (WA1HLR) said no difference in signal, Joe in Gerorga reported the G5RV a bit stronger.

    I also had my new MFJ loop antenna hooked up and did diversity between it and the other two antenna,s, and its very effective.

    I like the Drake tuna as I can switch between antenna's, through the tuna or not, and its got a band switch which makes things a bit easier
    then a roller inductor which also tends to wear out.

    If I had a different shack layout, open wire line into a good tuna would be the way to go I suppose, but its not going to work how things are set up here.
     
  5. N1BCG

    N1BCG Ham Member QRZ Page

    The third option is to use snap-on chokes to clean up the cable TV, phone, and internet issues and stay with the full-size (and balanced) antenna.
     
  6. N2DTS

    N2DTS Ham Member QRZ Page

    I tried all of that plus more, the problem seems to be outside the house at the pole.
    I disconnected the phone line and ethernet cables from the modem, put all sorts of filters on the power cord, tried an isolation transformer, and grounding all sorts of things all over and nothing made a bit of difference.
    Only moving the antenna away from the cable at the street cured the issue.
    And the antenna is at right angles from the cable.
    I could get the full size antenna about 10 feet away from the cable, the G5RV is about 30 feet away.
    No sign of any rfi now.
    I wonder if I was taking out other customers by getting in the cable.
    Most may be on fios which should be immune.


     
  7. K5UJ

    K5UJ Ham Member QRZ Page

    They will be since the power levels are not extremely far apart, but even so I would not rely on the kindness of others. I'd try to set up some kind of computer internet lashup to listen to myself on these networked SDRs scattered around the country especially east of the Mississippi and see for myself.

    I think your cable service has a problem. I used to get AT&T and radio was not kind to it because AT&T depends on the old twisted pair. I switched to Comcast (for other reasons) and that ended my disruption of the service. A vulnerability may be the modem since it's in a plastic unshielded box. As I recall, 160 m. or maybe it was 75, did the most damage. I don't think 40 m. xmissions were a problem.

    You really need to ditch the 8X. Save it for rx antenna feedlines and mobile operation if you do that. A common mistake hams make is thinking of coax in terms of its power handling capability, rather than its matched or worse, unmatched loss which gets worse the longer the run and the higher the frequency. This is something that gets QRP operators in trouble, and piss weakers who are already piss weak for other reasons besides power, are rendered more so because they think "I'm only running a Ranger so my 200 feet of 8X out to my <crappy antenna> is okay." Of all the hams operating, QRPers benefit the most from running LDF4-50, especially if they're on the high bands and the feedline is a few hundred feet. If I were one of these uh, sadists, I'd probably run 7/8 inch line. But anyway, you really ought to maximize the efficiency of all elements of your antenna system under your control.
     
  8. N2DTS

    N2DTS Ham Member QRZ Page

    Well, the coax worked fine for matched (very low swr) fan dipoles.
    The longest run was about 65 feet from the far dipole (no longer up) and the main antenna is right over the shack, so its just down from the antenna and into the basement, 50 feet...
    The current G5RV has the window line run down to about 4 feet above ground then switches to the RG214m.

    Moving the antenna away from the main comcast cable on the poles has cured my rfi issue. It was not a problem in the house.
    The cable may have issues, its old, and is actually laying on a big branch of my tree out front.
    I wonder if I could run a ground to it there.....

    Anyway, I have two real choices, use the G5RV which seems to be working very well, it has about 20 feet of RG214M to the tuna, that is a very short length of good coax.
    Or, I can put a shortened (loading coils) 80 meter dipole with a 40 meter below that (fan), and cut it to length to get low swr.
    I would still have to tune it on other bands and have a longer run of rg8x. Plus they tend to get tangled up in storms...

    I tend to think the G5RV would work better overall....there is not much loss in the antenna or feedline...
     
  9. W8KHK

    W8KHK Ham Member QRZ Page

    If the cable run is old and supported by tree branches, maybe Comcast could help.

    I reported the RFI problem here, and even though the antenna was not near the overhead run of cable, they came out and solved the problem. They took down the overhead run from the pole to the house. They ran a new line down the pole, and grounded it at the bottom of the pole. Then they ran line underground to the service entrance location, and grounded the cable where it enters the house. No more RFI problems here. No charge for that service, and the machine that buried the line was neat, and it did not mess up the lawn.

    My neighbor to the west also got the same burial service free of charge. And they had to run the line under their concrete driveway.

    Perhaps this method might allow you to put the long 75 meter antenna back in the optimal location.
     
  10. K5UJ

    K5UJ Ham Member QRZ Page

    Around 6 or 7 years ago my neighbors complained that I was knocking them off of the internet. They had Comcast cable. Testing revealed that 100 w. was okay, but above that and they'd get thrown off line. I went over there with my RFI tool kit I used to maintain and wrapped every wire to their modem with ferrite rods and beads and I think I put an AC line filter inserted in the power cord. That solved their problem but they had Comcast cable man come out anyway. He pronounced their cable drop defective with bad connections and ran a whole new drop. After that I could retrieve my ferrite etc. and they were still interference free. So cable maintenance may be needed. The RG6 used for this is pretty good cable. Google Belden RG6 drop cable and you'll get it I think. They also use good connectors and crimp tools. A lot better than the ones sold at hamfests.
     

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