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Receive Antennas (below 30MHz) For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum.

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Old 01-05-2014, 1:46 PM
   
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Default Too Long?

Can you actually get too long with a long wire antenna for short wave listening? I see a lot of post's with the 100' length being the longest. I could stretch much more than that if I wanted to but at what point is it useless to go any further, if there is such a thing?
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Old 01-07-2014, 2:59 AM
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Depends on your environment. If you have any local transmitters on the AM band, then they can overload the early stages of your radio if your antenna is too long. You will hear the stations even though you're not tuned to them! Otherwise go for it! Some guys out in the boonies have Beverage antennas miles long!
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Old 01-07-2014, 6:21 AM
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More to the point - as you get really long - say 300 foot or perhaps a bit less - some antenna designs will start to become bidirectional off its ends, depending on the frequency being listened to and how high the antenna is off the ground.

Majoco is perfectly correct about pointing out the possibility of overloading. Folks that put up real long antennas - for DXPeditions, frequently - are using desktops which tolerate high levels of RF far and away better than most portables. Even a Eton E1 would lkely choke at a 300-400 foot antenna, especially so if the receiver was near an urban area where there's lots of MW and FM stations around. If you're using a R75, Alinco R8 or an older desktop like the Drake R8 series or the AOR7030, they're more likely to handle this without much fuss

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Old 01-07-2014, 9:16 AM
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I am using a full 160M Dipole for my Utility monitoring. Full length end to end approx. 246' . I have it on a non-amplified 4 port multicoupler that imparts a 12dB attenuation per port. Two of the receivers have an additional 10dB pad in line, the GlobalTuners - On-line remotely controlled tuners Icom ICR-1000 has a MW (AM broadcast band filter) and a 3dB pad to avoid overloading the front-end.
The only radio that does not have additional attenuation in the coax is the WinRadio WR-G33DDC. and I usually keep the 3dB built in attenuation engaged as it helps reduce the noise floor.

So, long story short, too much antenna can be a problem, those problems can be ameliorated but it may be easier to keep the antenna matched to the receiver.

However as the article in this month's The Spectrum Monitor points out, electric fence wire is cheap and if you have time and the inclination, experiment, It is fun to and instructional to string wave traps .

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Old 01-07-2014, 11:55 AM
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The longer the antenna, the more directional off the ends it will be. This applies to SW as well as lower frequencies (like MW, which most of the ultra long antenna aficionados seem to use them for).

The ARRL Antenna handbook has charts showing how the receive patterns appear with your antenna at different wavelengths. They go from a cloverleaf at a full wavelength to more and more lobes -- increasingly off the ends of the antenna -- the more wavelengths your antenna has.

A 300 ft. antenna would give you some directionality off the ends of the antenna at 30 meters (300 ft. being roughly 100 m, which is roughly 3 wavelengths at 10 mhz) -- with an antenna like that, you'd still hear stuff off the sides, but the reception off the ends (or diagonal to the ends of the antenna) would be more pronounced on the 31 meter band, and a bit more so on the higher SW bands (a bit less so on the lower SW bands).

But like the others said, local transmitters can overload your receiver if you're in the vicinity. If you live far enough away from local AM stations, a 300 ft. antenna may be worth trying on SW, just make sure the ends are pointing more or less in the direction of the parts of the world you want to hear the most.

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Old 01-07-2014, 3:27 PM
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Quote:
Originally Posted by dac1979 View Post
Can you actually get too long with a long wire antenna for short wave listening? I see a lot of post's with the 100' length being the longest. I could stretch much more than that if I wanted to but at what point is it useless to go any further, if there is such a thing?
As you can see by the responses, there can be many answers There is not simple answer, and there is no one “right” answer.

I am going to assume you mean an end fed random wire antenna and not a long wire. A long wire is by definition over one wavelength at the operating frequency of choice, so a 100 foot end fed wire is not a long wire unless you are talking about frequencies above 9.3 MHz, below that frequency it is just a random wire. If your goal is the performance of a true long wire (and associated directionality) then there might not really be too much wire until you get to several hundred feet at say 10 MHz.

You can’t discuss random wire antenna length and how that plays into things until you discuss frequency and what radio you are using. With a portable, you certainly can end up with too much wire in the air. With a desk top mostly this is not an issue unless you live close to an HF or MW transmitter. As has been said, a random wire can have directionality (increasing as length increases or as frequency goes up for a fixed length), and can be used to your advantage with a little thought. A 300 foot random wire would have some serious pattern shaping going on at 25 MHz, but be rather non-directional at 1 MHz. If you want an all HF band random wire antenna then going beyond 100 feet is probably not going to be too much of a general purpose plus, I typically find that about 75 feet is all the random wire antenna I have wanted.

With that said no one antenna does it all. I find that if you have the room multiple antennas is the way to go, some big, some little. And wire antennas can be inexpensive to experiment with. Build one to try out, if it does not work out for you use the wire and parts for another experiment.

My most used general purpose HF wire antenna is a full size tri-band fan inverted-V, 160 / 80 / 60 meters. One feed line for all three and each band on a different bearing. This means the 160 portion is about 250 feet long, the 80 meter portion is about 120 feet long, and the 60 meter portion is about 86 feet long. By selecting the direction each wire is laid out I was able to fill in some nulls and enhance reception in desired areas for specific bands. While that is my most used general purpose wire antenna it is not always the best.

For other wire antennas I also have an 80 meter full wave sky loop (257 feet of wire), 40 meter inverted V (66 feet of wire), 2 element 160 meter wire beam (250+ feet per element), 6 MHz dipole (78 feet of wire), 6 MHZ V-beam (390 feet of wire), three Rhombics of various sizes and directions (750 to 1100+ feet of total wire in each one), and a 25 and a 75 foot random wire.

From 40 meters up I generally do not use wire antennas as much as other antennas when the going gets tough. I still use wires, but most of the time when reception gets rough I use something else up there, the SteppIR, a Yagi, something.

T!
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