Long/Random Wire Height - Does it Matter for RX?

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ultravista

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I want to run a few long/random wires for receive only. My property footprint is small and I have to get creative.

One wire will rise 40 feet vertically then slope down to a corner of the property, perhaps another 40-50 feet.
The other wire I am thinking of running along my cinder block side and back walls.

The wall is approximately 6 feet, 10 feet, then 8 feet (yes, different sizes) around the perimeter of the back yard. I could get about 60 feet of wire out on the wall.

I have seen people running their wires along wooden fences and I would like feedback on running along the cinder block wall.

Must I elevate it above the wall or will 'close to the top' suffice? Would it even be worthwhile to run it along the wall?

Does elevation come into play with a long/random wire?

I am also wondering about the vertical, how I may improve receive efficiency. Any ideas?
 

wyShack

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What bands are you trying to pick up? Most radios today have more than enough sensitivity and the big culprit for receiving is noise from other sources. Remember you are trying for the best signal to noise ratio-not the highest signal level. I have often had better luck getting the antenna 'away' form the noise (like all the electronics in my house). If you have a way to run a coax out to an antenna away from other noise sources, you may be surprised by what you can hear with 30-40 feet of wire.

As most noise seems to be vertically polarized, I would suggest keeping the wire horizontal. A 30-40 foot doublet (coax in the center -like a dipole) up 15 feet or so with coax to your radio may work wonders. Another thing to remember is to ground the radio to your buildings ground-if you can run a coax shorted at both ends (with a .01 capacitor if you can) will help reduce the noise.

Most radios actually 'back down' the gain below about 15 Mhz due to noise-If you are lucky enough to be in a rural area isn't quite so bad but it is still the limiting factor compared to simple signal strength.

What are you running for a receiver? If equiped, you may try different gain settings and see where the 'best' results are.

Good luck and enjoy the hobby
 

prcguy

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Most people using a horizontal wire antenna for SW have it somewhere between 10 and 30ft off the ground based on running it from a 1 or 2 story house to a tree or some other attachment point in the yard. At those heights for some SW reception the antenna will have much less DX reception at a low angle to the sides compared to straight up and will work best for stations within a few hundred miles and not necessarily distant countries. At low heights the wire will also be fairly omni directional on the lower bands.

To get the best performance for distant stations thousands of miles away, a horizontal wire would need to be at a half wavelength or multiple half wavelengths off the ground to favor a low angle, which is not practical for most users. A half wavelength off the ground at 15MHz is about 31ft, but for 5MHz it would be about 94ft. At 3Mhz it would be 156ft and so on.

Then you have the problem of gain lobes and nulls when using a long random length of wire to cover a large frequency range like the entire SW bands. If you put up a 50ft wire broadside to your favorite country, it might work ok at 5Mhz where the antenna might have a lobe broadside, but at 10MHz there might be a null broadside and reception is 10dB or worse compared to running the wire a different direction for that country.

Antennas are complicated but fortunately SW reception is somewhat forgiving. If you do a little research and understand what makes an antenna do various things, you can make better use of your wire and get better reception.
prcguy
 

WA8ZTZ

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For medium wave and below would include the AM broadcast band and the longwave frequencies... NDBs. Generally speaking for those frequencies you want your wire antenna to be as long and as high as possible and away from the house (which can be a noise source).

You don't mention what receiver you are using, but if it has a typical 50 ohm antenna input, a 9:1 matching unun at the feed end will help greatly when using a random wire antenna.

If running stranded wire, use insulated wire because uninsulated stranded wire will eventually oxidize between the strands and the antenna will get noisy and also be a potential source of undesired intermodulation products.

For AM BCB especially, you may want to do some reading on various loop antennas. They have the ability to peak desired signals and null undesired signals which is very useful on the crowded broadcast band.

You say that your property is small so let me suggest the ApexRadio 303WA-2 vertical. Have used it here with absolutely amazing results on AM broadcast band and longwave.

Anyway, just some food for thought. Most SWLs and hams are constantly experimenting with different antennas so go ahead and try out your ideas and see what happens. Most of all, be safe... stay away from overhead electric lines for both noise and safety reasons. The idea is to have fun and enjoy the hobby. :)
 

ka3jjz

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Loops are definitely the weapon of choice on MW and below, unless you have LOTS of land to string up Beverages in different directions. The advantage is simple - you can turn them to null out interfering stations and/or sources (something you can't do with a vertical). There are numerous plans for such on the web; we have just a few of them in our loops wiki;

Loops - The RadioReference Wiki

Note that some of the pre built ones like the W6LVP loop tune right down to 135 Khz. I think the Pixel and Wellbrooks go down a bit further than that.

and for LW stuff, there's no better reference than the Longwave Club of America. No doubt they have tons of loops plans out there

http://www.lwca.org/

Mike
 

ultravista

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I have the SDRPlay RSP2 (with built in high Z port) and RTL-SDR V3 dongle that I use with a 9:1 unun.

In addition to my quest to build an efficient long/random wire, I have an active whip, PA0RDT, from Roelof in the Netherlands.

What about a loop created from the long/random wire? I have enough wire that I can create a loop instead of a sloper - perhaps a pennant of sorts.
Does it need an amplifier or will a 9:1 unun work?
 

ka3jjz

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How you could hope to derive an efficient wire antenna from an active whip is beyond me...the two could not be more different, and both react in completely different ways to a signal. Active whips are notorious for being able to hear noise as much as anything else unless you can get them out in a quiet environment, away from the home and other noise sources. Not the best choice for most, IMHO.

Unless you have a huge amount of land, most wire antennas on MW and below tend to be very inefficient. This is because that even a 100 foot wire is electrically too short to be very efficient on these bands. Yes, you will hear stations, but the antenna won't be performing optimally. In addition you can't rotate or null an interfering station or source to bring in the station you really want to hear.

You most certainly could create a loop from the wire you would use for a random wire, although there are designs that actually use a hunk of coax as the loop itself. It is likely that you will need some sort of matching unit or amplifier because most small loops are (once again) a fraction of the size needed to be efficient, particularly on MW and below. There are numerous books and sites on the web with the plans. I'm pretty sure Joe Carr has at least 1 or 2 books on the subject. Insofar as MW goes, the 2 well known clubs - the International Radio Club of America and the National Radio Club - that specializes in this band will, no doubt have lots to say on this matter.

I would strongly urge that you go buy some books and reading up on the subject. While it's worthwhile (and instructive) to experiment - and you will not damage your RSP2 in the least if you put something together that doesn't work well - antennas are as much a science as art. There are some principles that you need to comprehend in order to put something together that works well. This takes some study to learn. Taking the time to learn now will pay off handsomely in dividends later. There are no easy shortcuts here.

Mike
 

WA8ZTZ

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Be advised that you may experience overloading of your SDR on the AM band, especially if you have AM stations nearby. Some preselection, a tuner, or filters may be necessary ahead of the receiver. On longwave, you may hear "images" of strong local AM stations as you tune across the NDB band.
 
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