Novice question on SWL longwire and g5rv

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K5GHM, Nov 27, 2019.

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  1. K5GHM

    K5GHM Ham Member QRZ Page

    Receiver sare a Tecsun pl-660 and a RTL-SDR I'm experimenting with. I have 2 antennas that I trade off with. The Longwire is a 70' copper strand with a 9:1 balun and 8' ground. The Dipole is a G5RV design at 51' each side for 102' total that I installed about 2 days ago. Both antennas are coated with no bare wire showing. At present they are both strung along a 5' wrought iron fence about 100' long. Both feed lines are presently laying across the yard until I can get them underground and lawnmower proof. In my previous residence I strung these same antennas along a wood fence. I get good performance from both but I'm always looking for even better performance.

    Will stringing these higher in the trees about 10-20 ' make a huge difference? Or maybe stringing them in the attic which will give me about the same height. I've got several acres to play with.

    Does stringing along the metal fence compromise performance? I honestly can't tell a lot of difference from the wood fence configuration at the old house.

    Before I go buying more feed line and stringing wire in trees or climbing in the attic I want to get a rough idea of what I can expect. I'm still learning this stuff so any and all ideas, advice and recommendations are appreciated.
     
    KN4SKF likes this.
  2. WG7X

    WG7X Platinum Subscriber Platinum Subscriber QRZ Page

    If you have several acres at your disposal, get to stringing wires in the trees, up as high as you can get them. They will work very well, and are usually almost invisible.
     
    K5GHM and KN4SKF like this.
  3. KN4SKF

    KN4SKF Ham Member QRZ Page

    Great Question, also as a new ham, I am looking for some good comments.
     
  4. WA7ARK

    WA7ARK Ham Member QRZ Page

    The pattern of a horizontal antenna only 5ft agl is straight up, with almost no signal near the horizon, where you want it to be... Laying it on a metal fence is like grounding it...

    For any reasonable performance, it should be a minimum of 1/8wl agl (~18ft for 40m), and 1/4 to 1/2wl is much better.

    The "longwire" is really a Marconi vertical antenna, and as such needs to be connected to a large radial field (counterpoise) right below its near-earth feedpoint. Then it needs to go up a minimum of 1/8 to 1/4wl and then the rest of it can run near horizontal as an inverted-L. Alternatively, it can run from the near-earth feedpoint at an angle to a tree top. Running it horizontal at 5ft agl is not useful...
     
    Last edited: Nov 28, 2019
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Yes, moving from 5' high and in close proximity to an iron fence to 25' or 30' high and in the clear should make a very big difference.
    Only put antennas in an attic when you have no other choice. Building materials tend to attenuate signals and proximity to household electronics noise can create RFI havoc with attic antennas. Sometimes there's no other choice but that does not appear to be your situation.

    If you'll only listen with these antennas they really don't have to be well tuned or matched though that never hurts. If you'll eventually transmit into these antennas then impedance matching is important.
     
    K5GHM likes this.
  6. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Anything you do with those antennas will be better than draping them on a 5ft tall iron fence which is sucking signals in. :)

    The Random/Longwire would be improved by adding radial wires. Longer and more are better.

    Both antennas would benefit by elevating them and/or moving them away from metal objects.

    Enjoy your experimenting! b.

    p.s. Let's do the math...

    70ft/3.3 ft per meter = 21.212 Mhz wavelength. So, your end fire wire is only a "Long Wire" for 15 meters band and above.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I agree 100%.

    Very big difference. And higher would be better, if you can get above 25-30 feet. Even if that means the antenna is very far away from the house and you need more coax....definitely worth it. In fact, "far away from the house" is almost always better for reducing noise levels which originate in the house!
     
    K5GHM likes this.
  8. KK4NSF

    KK4NSF Ham Member QRZ Page

    For shortwave listening, the requirements are a bit different than they are in ham transmitting. I do a lot of both, and have come to love my loop antennas for SWL. They don't take up a lot of room, don't require a tower, and are directional.

    My current Receive-Only loop is a 5ft square, with a simple impedance matching transformer, built on the same lines as: http://www.kk5jy.net/rx-loop/ by Matt Roberts. Mine is a bit bigger, with more capture area... and thus more gain... but it works just the same.

    Without an external pre-amp, it has enough gain to overload my SDRplay on stong stations on strong signals if I don't tune it down (or turn it to null out the offending station) .... and pull in very weak signals. Just this afternoon, I was listening to the BBC Station near Manila in the Phillipines on 49m, and get Radio Romania nightly, not to mention the Supreme Master Station and a British Pirate.

    If you aren't yet into building stuff, you might want to look are MFJ's Receive Only Loop: https://www.mfjenterprises.com/Product.php?productid=MFJ-1886
    I've used one several times, and for what you want to do it is VERY good.

    Dave
    KK4NSF
     
    K5GHM likes this.

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