Looking for guidance on what I should do and what I'm doing wrong

Discussion in 'General Technical Questions and Answers' started by KE8LMF, Feb 16, 2020.

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  1. KE8LMF

    KE8LMF Ham Member QRZ Page

    Equipment
    • Icom 7300
    • SEC-1235M
    • MFJ-347
    • MFJ-1699T
    I'm now starting to think that the MFJ parts I have (347 and 1699T) aren't ideal for what I want.

    I currently rent a small home and I'm hoping to buy a house this year. So, I am trying to avoid a wire dipole until I have my own house. However, I'm starting to think I should go ahead and get a wire dipole.

    I don't seem to have any trouble receiving, only transmitting, which I expected. When I transmit my Icom shows a very high SWR, sometimes infinite. So I've been working on getting my SWR lower before I damage something.

    My radio is in the house and my antenna is outside. I've read a good bit on grounding, but I am having trouble understanding it. There are a lot of really smart hams out there and I'm hoping they can tell me what I need to do for my situation. As I continue to enjoy this hobby, I hope to understand what all this means. For now, I'll settle with safety and enjoying the hobby.

    I have a 4" choke at the end of the RG8X.

    How can I properly ground everything, operate safely, lower my SWR, and improve my setup?

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  2. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    You're going to have to put a ground plane under it, but that's such a poor antenna for any bands other than 15 to 10 Meters I wouldn't bother. My son tried running one of those mobile on 40 meters, I couldn't believe how poor it was, even a hamstick Beat It by quite a margin.

    Get up something else if you possibly can,
    33 ft piece of wire would work better.
     
    Last edited: Feb 16, 2020
    KE8LMF and K7TRF like this.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    As posted above you really need a ground plane which means either a few elevated radials or quite a few ground radials and not just a ground wire to a ground rod. Ground rods are great for low frequency AC safety grounds and can be helpful for lightning induced power surges but they make terrible RF ground planes which is what you need for a vertical antenna like this.

    But even with a good field of radials this tapped mobile antenna is not going to be a great performer on the lower frequency HF bands such as 80m or 40m and probably only marginal on 20m. There are a lot of approaches you could take, a simple tuned wire dipole is a very good way to go but a taller vertical trapped or loaded over a decent set of radials or an End Fed antenna with appropriate wire length and feed point transformer would almost certainly out perform the antenna you have.

    But if you really want to get this antenna to work half decently you really need a set of radials or equivalent ground screening below the antenna. Remember this was basically designed as a mobile antenna solution which means the expectation was to mount it on a vehicle chassis and in that case the vehicle's body and chassis serve as the ground plane which you don't have in your installation.
     
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  4. WA4SIX

    WA4SIX Ham Member QRZ Page

    Cutting the extension cord up for a dipole would be better.
    Not trying to burst your bubble, but you will honestly need 1 full wavelength per band you want to use (twice a dipole per band) of wire just to make that thing think about working poorly.

    Ed
     
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  5. N8MLP

    N8MLP Ham Member QRZ Page

    You could also look into a portable type vertical... there is a sweet Buddy Pole in the marketplace right now.

    Wolf River Coils has some very nice antennas too

    The idea is, get on the air now. Then when you have your more permanent solution you can use your vertical portable.
     
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  6. AI3V

    AI3V Ham Member QRZ Page

    Read this book:

    https://archive.org/details/SimpleLowCostWireAntennasForRadioAmateurs

    Go to the hardware store, and buy this:

    [​IMG]

    That's 500 feet of 14gauge stranded wire.

    Todays price is $43.17

    While you are there, buy a length of 3/4 or 1 inch diameter pvc pipe for insulators. If you are ca$h rich, maybe a 4" or so diameter piece for coil forms :)

    Some guys go to the tractor store, or the farm supply place and use electric fence insulators.

    Then go to the chinese tool store and buy a spool of this stuff:

    [​IMG]

    600 feet of 1/4" polypropylene line, this is going to set you back another $16.99

    Use your imagination to get as much wire up, as high as you possibly can.

    Some ideas:

    Half a brick, tie rope to it and toss it over something:

    [​IMG]

    Slingshot; I had one, used a 4 oz fishing weight and some 20 pound test line

    [​IMG]

    Or a giant slingshot (big shot line launcher:

    [​IMG]

    This would be uber cool:

    [​IMG]

    Mossberg 590 line launcher kit.

    :)

    Rege
     
    W6KCS, W2CHZ, K6CLS and 3 others like this.
  7. KA0GKT

    KA0GKT Ham Member QRZ Page

    It looks like you have one of those gadgets which allow you to tke two loaded antennas and make them into a shortened dipole. As youi are using it, all you really need is the side which has teh SO239 (UHF Female) connector along with some ground radials.

    Now to the SO239 side of things.
    Is there a reason that the shoulder on the insulated washer isn't going into the hole through the mount so isolate the center conductor from the (supposedly) grounded mount? From the photo, it looks like it is installed upside down.

    Get rid of the jumper which runs to the other 3/8-24 coupler. It is possible that the connector there might be grounded.

    Run a radial for each band on the ground under the antenna and then check the VSWR. You may be surprised with a low VSWR. Oh and do your VSWR checks at as low power as you can get full deflection on teh VSWR bridge. You ought to be able to do it with only a couple of watts power output.
     
    KE8LMF likes this.
  8. KE8LMF

    KE8LMF Ham Member QRZ Page

    Thank you all for the help! I'm going to read through these and do some more research :)

    Would you care to elaborate on using a 33 ft piece of wire? Or send me a link?

    I was thinking about getting the MFJ-1779C
     
  9. KA0GKT

    KA0GKT Ham Member QRZ Page

    246/33=7.4545

    246/frequency in MHz = 1/4 wavelength
    246/ length of 1/4-wavelength radiator = Frequency in MC/S
     
  10. KJ3N

    KJ3N Ham Member QRZ Page

    Something about a mouse and an elephant gun comes to mind.....
     

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