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Random Length Wire Antenna

Discussion in 'General Technical Questions and Answers' started by KD8HYU, Aug 28, 2008.

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  1. KD8HYU

    KD8HYU Ham Member QRZ Page

    I am currently studying for my general and hopefully soon (when the money shows up) getting an FT-857D. I am unsure when I will be able to take my test but for the time being I would like to just listen to the HF bands to try and learn as much as I can.

    I am living in an apartment on the top floor with access to the attic :D (great landlord so far... HE SUGGESTED I USE IT!!). I was thinking that with just wanting RX I could use a random length of wire and be able to hear something, hopefully...

    Is there any specific length I should shoot for or any other type of antenna I should try and put in the attic?

    Thanks in advance for any help!

  2. KD6WAG

    KD6WAG Guest

    Yes. Get a standard banana plug (around .49cents) from any electronics supply place. get a long legth of wire. The longer the better preferably. Connect the wire to the banana plug and just plug it into the hole on the HF SO-239 connection on the back of the radio.

    If you can, elevate the wire up into the rafters or.... Since you said you're upstairs, you could hang it out the balcony/window going down. Just make sure it's not in an area where someone could pull on it, causing your 857d to "fly" out the window.

    Just make absolutely sure you DO NOT transmit with that lone wire. It's fine for RX, but not TX. You'd damage your finals without a proper counterpoise and proper tuning of your antenna. Listening, you're all good. A simple wire works very well. I used to do what you're doing when I too was a tech. Lots of fun. Although 160M never came in. I didn't have a long enough wire.

    Being a "tech," you're still permitted to talk on all of 6M and a portion of 10M (28.300-28.500 mHz). 28.400 USB is the calling freq for 10M and probably the busiest place to start listening. 50.125 USB is the 6M calling freq and again, when conditions are right, that freq. will be busy too. Just for starters........

    This is just my opinion. Due to really rotten propagation conditions, you'll probably hear the most "talk" on 20M USB. It's good day and night most times. More so than any other band in my opinion. There's usually a net all day long on 14.300 (Maritime Mobile Net). It's at least good to hear people there to see if your "receive only" antenna is working. But also, spin up/down the dial to make sure. 40M is good too.

    At night, 80M comes alive more. Right now, not much happening on 10M or 6M, but it opens throughout the day. Sometimes it booms in, and sometimes you may not hear anything at all on those bands. Mostly because it may be open, but knowbody is on the band giving it a shout.

    Just don't get discouraged if you don't hear anything. You may have to play around a bit with the length of the wire receive antenna, but you don't have to be exact. It works pretty good.

    Let us know what you did and what bands your heard with your experiement!

  3. G4ALA

    G4ALA Ham Member QRZ Page

    Tuning a wire without transmitting


    The problem with a random length of wire is that it really needs tuned if it is to work efficiently.

    Tuning a wire generally and conveniently requires an SWR meter and some transmitter power.

    If you cannot transmit there is a problem with such a setup.

    The problem is now solved by the MFJ 212. You will still require an ATU. You probably were going to buy one of these anyway, looking forward to your transmitting days. The ATU does not require an SWR meter if you use an MFJ 212. The ATU can be a very low power rating device.

    The MFJ 212 is a white noise generator which, when the MFJ 212 is switched on, puts out a white noise signal across all of the HF bands. The white noise generator is coupled to a 50 Ohm RF bridge circuit with the antenna wire as the measured load.

    The output of the RF Bridge circuit, when the MFJ 212 is switched on, is coupled to input of the receiver and the white noise generator creates wide band white noise. When the MFJ 212 is switched off, the antenna is switched directly to the receiver input and the noise generator is switched off.

    Simply connect the MFJ 212 between the receiver and the ATU. Attach the random wire to the input of the ATU with a banana plug as described. Tune the receiver to the frequency you wish to hear. Switch on the MFJ 212 and adjust the ATU for minimum noise by listening and/or looking at the S meter reading. When you achieve the best dip you can, the antenna is tuned to 50 Ohms. Switch off the MFJ 212 and listen to the difference it makes.

    The MFJ 212 is also RF protected up to 300 Watts. It will still be useful when you achieve your transmitting license.

    Part of the appeal of the MFJ 212 is that it allows antenna tuning in HF broadcast bands, where transmitting is not allowed.

    In trials, on the Ham bands, after a little practice, I was able to adjust the ATU for an SWR better than 1.3:1 using the MFJ 212 alone. The SWR reading were confirmed by using an SWR bridge and RF power into the MFJ 212 tuned wire.

    Hope this helps a lot of people, especially Short Wave Listeners, who need to tune an antenna.


  4. K3WRV

    K3WRV Guest

    Your random wire will work, but without a tuner, it's going to be receive only. As far as length goes, longer is better, but I've used 5 foot test prods from a VOM and hear stations.

    If you buy a tuner and plan to keep using a random wire when you get your license, the MFJ 16010 works pretty well. for receive, just peak the noise and you should do OK. But you'll do fine without it.

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