Antenna for limited space

Discussion in 'Amplitude Modulation' started by N2DTS, Jul 16, 2020.

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  1. N2DTS

    N2DTS Ham Member QRZ Page

    I know a dipole fed with open wire line and a balanced tuna is a good setup, but at my location it would be a bit hard to bring in OWL and have a tuna handy.
    Plus, every time you change bands you have to tune, even to listen.
    Some modern gear makes it a snap to switch between bands, or you can have transmitters tuned up for various bands that makes changing bands very quick and easy.

    I have limited space and now limited supports for antenna's and have an 80 meter dipole over the house, right over all the TV and internet stuff and not that high up. 80 meter high power operation takes that out.

    I have an Alpha Delta LB plus that actually works ok, its great 40 and up as its a full size fan dipole there, for 80 and 160 its loaded and the loading coils act like traps.
    Because of the coils, it does change swr in the rain, and has a narrow bandwidth like any loaded antenna.
    But that antenna is off to one side of the house and does not take out the TV and internet.

    I don't do 160 as the antenna is really short and would not work very well, so I think I will remove that part and the 80 meter coil part, and just add an 80 meter dipole as long as I have room for and make some small loading coils at the mid points to get the swr low.
    80, 40, 20, 10 and I might add a 6 meter leg.
    Low swr means low loss on the coax (65 feet) and no tuna needed with the tube rigs.

    The Alpha Delta antenna's are made with number 12 or 14 solid insulated copper wire with plastic spacers and copper wire twisted around the antenna legs and the spacers.
    That seems to work well, unlike some of the ones I have made they do not tangle up in the wind.
    The full size legs seem to change very little in the rain, the coils do.

    In stock form, the coils they provide do not hold up for a long time, UV gets to the enameled wire in the coils and it degrades, but the antenna does work well when new and allows all bands in a limited space.

    It happens that the current Alpha Delta lb plus I have up is very low SWR on 80 and 40 meters where I operate and I have been able to put 300 watts into it on 80 meters and not take out the cable stuff.
    I plan on removing the 160 and 80 meter coils and adding as much of an 80 meter leg as I have room for to improve the efficiency.

    If making a fan dipole, solid wire seems to work much better, less tangles.
    I have access to free wire at work (scrap) but its all stranded, no good for fan dipoles.
     
  2. W2VW

    W2VW XML Subscriber QRZ Page

    We might have done this before but....

    Brett, you have enough skills to build an effective antenna tuner which can be reset by dial markings.

    Just use good turns counters. Record dial positions for different bands and operating areas.

    When you move frequency just set to your cheat sheet. No RF or SWR measurement needed.

    A well built antenna system should not need retuning when it rains. Well implemented balanced feeders do NOT radiate one iota of RF.

    Avoid link coupling if you wish to use the antenna to receive on all bands without retuning. Link coupling is bandpass.

    Look at Billy's (W2BTK) antenna coupler circuit. His antenna is about 30' over his house which is loaded with modern electronics which work fine. BTK can receive all of HF without changing settings.

    Limited space dictates one good balanced antenna and a system to deliver power effectively without wrecking balance.

    Credit card antennas are a one way trip to Palookaville.
     
    AG5CK likes this.
  3. N2DTS

    N2DTS Ham Member QRZ Page

    He still has to tune the tuner, move jumpers on coils, and he runs a lot less power then I do, 1/4 of the power or less.
    I have tried the tuner and one antenna many times before and do not like it.
    I also dislike iron core baluns at qro power levels.
     
  4. W2VW

    W2VW XML Subscriber QRZ Page

    Yes his tuner is not yet setup for quick changes but the point is RFI can be eliminated with a careful setup. It is easy enough to adapt that circuit for reset-ability.

    BTK runs legal limit when things get noisy.

    Balun Designs' ferrite core 1:1 balun works fine when terminated with 50 ohm J0 like it is with the coupler shown. Zero increase in core temp at 1500 watts.

    Anyway to each his own. That's what makes amateur radio fun.
     
  5. K4KYV

    K4KYV Subscriber QRZ Page

    Better still, use a balanced tuner with a split-stator capacitor, not one of those bogus unbalanced L- or T- networks feeding the OWL through a balun. Then you won't even need the turns counter. Just one or two 180° dials with a 0-100 scale.

    Plug-in coils work a lot better than trying to band-switch. The plug-in coils can be configured to automatically change to series to parallel tuning as needed when you plug in the coil. To change bands, just plug in the appropriate coil, adjust the dial to the pre-set according to the tuning chart and you are ready to go.
     
  6. N2DTS

    N2DTS Ham Member QRZ Page

    That is a very good idea Don, I like plug in coils.
     
  7. AG5CK

    AG5CK Ham Member QRZ Page

    Dave set me down the right path on tuners before I bought some junk. My doublet is currently 76 feet long with about 35 feet of feedline.

    I run coax out to a doghouse at my tower. I can step out the back door and change bands quickly enough.

    I use a link coupled tuner in series configuration for 160 and 75m. The reason is that my short antenna is narrow banded and I can move around the band easier. I have a motor on the variable cap and a switch on my desk.

    The balanced L covers everything else. The antenna has enough bandwidth on 40 and down that I can set it and forget it.

    The ladder line is made of #8 thhn. I almost wish I would have used #6. A 1500 watt test carrier for a minute or 2 will warm it up.
     
  8. W2VW

    W2VW XML Subscriber QRZ Page

    L and T with a balun following are for the electronics uninitiated.

    There are much better networks which will work into less than 50 ohm with reactance loads without melting.

    Most people asking for help these days have limited real estate.
     
  9. WZ5Q

    WZ5Q Ham Member QRZ Page

    Exactly, works FB here on my 288' Doublet on all bands, 160m - 6m.
     
  10. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    I am space limited as well and for transmit I use a 43' base insulated vertical with a 1:4 UNUN. 20 buried radials round out the radial field.

    These UNUNS are easy to make.

    Now for 160m and 80m I use a modified Phil Salas switched loading system to load it for those bands.

    For receive, I use a Beverage.


    Pheel



     

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