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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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  #1 (permalink)  
Old 01-10-2017, 11:47 PM
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Default Long wire antenna question

Hello all....I got a question about a old longwire antenna I bought 20 some years ago from radio shack.

I've had my longwire in my attic for years cause of outdoor restrictions and I'm currently making a 9:1 balun or unun (whichever it is) that wi also have a ground terminal on it. After reading and seeing several articles and pics...I was wanting to know the best options. Some say to mount the balun directly (or as close to the longwire as possible) others say to mount the balun to the feedline and keep the ground wire as short as possible. If I mount the balun close or directly to the longwire and use decent coax to bring it to my radio (roughly 15 to 20 feet) my ground wire from the balun will probably be the same length to go to a grounding rod outside. If I mount the balun in my room to the feedline that came with the antenna which is a single maybe 18 gauge shielded wire that I'm currently using..my ground wire may be about 5 feet or so to ground rod. This antenna is used on a old radio shack dx-392 so I won't be transmitting at all on it.

So basically what I'm asking is

1- is it better to mount the balun at the antenna and directly tie the longwire to it and do away with the 18 gauge feedline I currently have and have a longer ground wire or

2-mount it closer to the ground source and use the 18 gauge wire as my feedline to the balun and keep the ground wire a lot shorter

Thanks guys
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Old 01-11-2017, 12:15 AM
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I posted this in the wrong topic...can someone please move this to the antenna section for shortwave? I can't find a way to delete it...sorry guys
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Old 01-11-2017, 6:30 AM
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Put the UNUN at the end of the "longwire" and use coax (RG-58 would be fine) to feed the receiver. btw, the antenna may work fine without the ground or counterpoise.
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Old 01-11-2017, 7:33 AM
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Ok thanks...I've had this longwire about 20 yrs and I don't expect a unun to boost the signal...I'm trying to get rid of the buzzing and background static...it drowns out everything....also the wire I think is over 100 feet so I may cut it down to 65 or 70
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Last edited by venom6733; 01-11-2017 at 7:42 AM..
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Old 01-11-2017, 8:04 AM
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venom, Certainly getting the antenna and feedline away from the noise as much as possible is one solution, but that's not likely to get it all, particularly since you are restricted to having no outdoor antennas, as so many of us are these days.

You would likely be better served by trying to figure out where all that noise is coming from. That can be a tall order for sure, because there are so many devices out there that can cause noise and RFI. If you can hear this noise on the MW band then walking around the area with a Walkman or similar would act like a very crude signal sniffer. You may end up having to turn various devices off and on to see if you can pinpoint the offending appliance. And it could be more than one.

There is often no one solution, and sometimes not easy ones. GL with your search...Mike

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Old 01-11-2017, 8:50 AM
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I agree with KA3JJZ, if you're hearing noise now, you'll be still hearing it, balun/unun or no balun/unun.

Check switching power supplies and ethernet cables (which act as RFI transmitting antennas).

You could use that DX-392 and tune it to either MW or SW and walk around and narrow down the sources. MW is useful because a lot of RFI ends up down there and the MW antenna is directional (be aware that RFI can travel from the source through the house wires), and the SW can be helpful because a 392 isn't incredibly sensitive off the whip (in most regions) and if you have RFI blasting into the radio, you'll know you're near the source.

I found an RFI problem with my digital SW portable that way, using the whip. Actually, several RFI sources. One was a bad CFL lightbulb (still worked well light-wise, just was blasting out RFI, especially on the AM band), the other was a neighbor's washing machine a block and a half away.

Good luck, and have fun DXing once you get the antenna fixed up / RFI issue dealt with.
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Old 01-11-2017, 9:14 AM
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At first I thought it was a ac hum from the wall wart for the radio till I put batteries in it with the wall wart unplugged and still had it. The noise isn't on all the channels but it's enough to interfere pretty bad on the weaker stations. When I unplug the long wire and just use the telescoping antenna on the radio..I get the same sound but just not as loud ( but the stations aren't as loud either) so the longwire just raises everything up equally. I've turned off fluorescent lights, turn off puters & TVs....it's probably something in my neighborhood. I do have outdoor antennas it's just with the size of my property, the trees and the way my electric lines come in...I just feel it isn't safe outdoors at all. Thanks for the help guys and maybe I'll get down to the problem eventually
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Old 01-11-2017, 9:42 AM
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Leaking transformers and cracked insulators are well known sources of RFI, altho getting the electric company out there to fix it is yet another pain in the rump. Take your 392 out there and see if the noise increases as you get close to the lines (obviously, don't get TOO close).

In situations like this, any outdoor antennas like random wires (a true long wire is a totally different animal) would be best running at as sharp an angle away from the lines as possible, and as far away. This is one situation where a Wellbrook or Pixel/RF Engineering loop MIGHT help as these antennas are less sensitive to E-Field signals (where most noise resides). They're quite expensive, but it may be worth it.

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Old 01-11-2017, 11:44 AM
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I use my 392 here and there when I get bored with hdsdr and decoding p-25 and stuff like that. I'll get on shortwave and sometimes decode we-fax out of New Orleans, Boston and pt reyes California...just that noise is making it difficult I may go home and unplug it and use batteries and throw the main breaker in the house and that should narrow it down to something in my house or something outside. Back in the 90.s when I was living in a different part of town, me and 4 other people used base station CBs and some nights of the week we couldn't recieve because there was a loud roar of static that was 9+ db on everyone's meters. That would last a couple days and then get up the next day and it would be so quiet that u could roll back the squelch and barley hear static that barley moved the needle...for years that went on and the problem was never solved as far as I knoww
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Old 01-11-2017, 11:50 AM
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Quote:
Originally Posted by ka3jjz View Post

You would likely be better served by trying to figure out where all that noise is coming from. That can be a tall order for sure, because there are so many devices out there that can cause noise and RFI.

.
If there is electric wiring in the attic near the antenna, it is probably radiating the noise and your attic antenna is picking it up. Adding the UNUN may somewhat diminish the noise but you really need to find the noise source and eliminate the noise at its source. If everything in your house checks out clean then, unfortunately, the noise is from a source over which you have no control. If that is the case, look into a magnetic loop antenna or a noise canceling box such as an ANC-4 or MFJ 1026.
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Old 01-11-2017, 12:19 PM
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The longwire is at the very peak in the attic but since I'm getting it thru the telescopic antenna also (just not as loud) It could be anything...I'll look into it more when I get home after work
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Old 01-11-2017, 6:17 PM
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Another thing to take into consideration (which hasn't yet been raised here) is you may be dealing with poor SW conditions, and sometimes when conditions are very poor the AGC of your radio will elevate the level of the natural (or ionospheric) background noise -- especially if there are "auroral" conditions.

I've noticed this on MW as well as SW. It can sometimes sound like a low level AC hum, without the 60 hz cycle thing going on.
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Old 01-18-2017, 3:38 PM
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Well guys I got it all built this weekend and installed it in my attic...WOW...what a difference. I didn't ground it yet to see if that would help even more...the closest possible ground I have up there that (if it's even a ground) is a metal vent pipe for my kitchen sink which leads under the house and is connected to a cast iron 4" pipe that leaves my property. Anyway it was worth the effort to build from scratch and solder it all up. Here's a pic of the balun when it was done and a wefax pic I just got from Boston on 12.750Mhz at about 21:00 UTC...first of all I was barely receiving Boston at all before the balun
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Old 01-18-2017, 3:40 PM
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And here's the wefax from Boston...thanks for all the advice guys
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Old 01-18-2017, 4:36 PM
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Nice job... good to see that it works for you.

Have a couple of similar antennas here and neither one is grounded, but just for kicks you can try grounding yours, however, don't be too surprised if it makes it noisy.

btw, is your toroid ferrite or powdered iron and what material?
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Old 01-18-2017, 5:00 PM
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It's a t-200-2 toroid core powdered iron...I was following a guide someone wrote online about baluns ...I got it from jpmsupply.com for like $7 plus 2 or 3 shipping..
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Old 01-18-2017, 5:14 PM
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I ain't a radio genius or anything...I just started looking into solutions to problems with long wire antennas and started reading about it...lol
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Old 01-18-2017, 7:36 PM
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Instead of grounding your new balun you may get more noise reduction by adding an effective choke balun in the coax run between the antenna and radio, especially after the coax has passed by anything that can generate RF noise. This reduced my noise floor and I didn't even know I had a noise problem.

For the roughly 4 to 17MHz range you can wrap 12 turns of RG-58 coax around an FT-240-43 ferrite core which cost around $9. Using 10 turns will shift the frequency range up a little and adding a few turns will shift the range down a little.

A common way to wind these is to wind half the turns then cross over the core and wind the remaining turns in the opposite direction as in this link: current balun, current choke, choke balun, 50 ohm 1:1

I have a different and more elaborate version and it turns out my coax runs from my radios past a bunch of computers, routers, etc, which picked up a bunch of noise and routed it to my antenna on the outside of the coax. Installing a good choke balun near the antenna made a very noticeable difference in my noise pickup and adding another 1:1 choke balun near the radio helped a little more.

Your 9:1 type balun uses the coax as a counterpoise and the braid of the coax becomes part of the active antenna and subject to any noise along the path to your radio. You might leave 10ft or more of coax between the balun and choke balun so that gives the 9:1 balun some counterpoise to work against, then the remaining coax going toward your radio will be better decoupled from the antenna system.
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Originally Posted by venom6733 View Post
I ain't a radio genius or anything...I just started looking into solutions to problems with long wire antennas and started reading about it...lol

Last edited by prcguy; 01-18-2017 at 7:42 PM..
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Old 01-19-2017, 10:13 AM
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I might try that prcguy....I doubt I'll build a box for it, since it's in my attic. My coax runs by a computer also. This may sound dumb but is a "long wire" in any way directional ...as in if u have it running north to south u can pick up better from east and west and visa versa ??
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Last edited by venom6733; 01-19-2017 at 11:35 AM..
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Old 01-19-2017, 4:25 PM
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A wire antenna will be directional depending on frequency and height above ground. If the wire is a perfect 1/2 wavelength and fed properly it will have a broadside pattern to the wire and nulls off the ends when its in free space or multiples of a half wavelength off the ground. The same antenna used on lower frequencies like 1 through maybe 10MHz and 15ft off the ground will give it a strong pattern straight upwards and mostly omni directional with very diminished performance at the horizon, where you need it.

A full wavelength antenna in fee space or multiples of 1/2 wavelength above ground will have a clover leaf pattern with four lobes, two wavelength long it will have a clover leaf pattern with eight lobes, and so on.

As an example, I've been using long wire type antennas for HF amateur use for many years and currently have an offset fed 80m dipole about 133ft long and 30ft off the ground. It has a fairly omni directional pattern at 3 and 7Mhz and I'm happy with it there, but its about 1/2 wavelength high and two wavelengths long on the 14Mhz band and about four wavelengths long on the 28MHz band where its got good low angle towards the horizon, but lots of lobes and nulls.

Unfortunately the way its strung up it sucks to the east of me (I'm on the west coast) because there is a null on those bands toward people I would like to talk with and its impractical to rotate the wire antenna to favor the direction I need on the upper HF bands. I finally broke down and put up a rotating directional antenna for the upper bands and it works way better than the wire antenna on 14 through 28MHz.

So yes, you can have a wire antenna and it can be directional and it can work lousy in a direction you might want. You can measure the length of your wire, calculate what frequencies it might be a 1/4, 1/2, 3/4, full wavelength, etc, then look up a chart on what the radiation pattern will be for a particular fraction of a wavelength to see if you are missing anything.
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Originally Posted by venom6733 View Post
I might try that prcguy....I doubt I'll build a box for it, since it's in my attic. My coax runs by a computer also. This may sound dumb but is a "long wire" in any way directional ...as in if u have it running north to south u can pick up better from east and west and visa versa ??

Last edited by prcguy; 01-19-2017 at 4:29 PM..
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