Odd Long Wire Antenna Issue

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ultravista

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I am using 24 gauge cross-connect wire (single pair) for my random length long wire antenna coupled to a Nooelec 9:1 balun.

In it's previous version, the wire ran vertical approximately 30 feet - the first 20 feet of the mast being galvanized fence post and the final 10 feet PVC. The wire ran through a metal loop at the top of the PVC down to a point in the yard, then across a cinder block fence to the end of the wire.

The wire was not tethered to the mast but hung loose up to the tip. It was not touching the galvanized pipe.
With a single wire connected to the balun, SW was pretty good and broadcast AM was attenuated well but was noisy. With both wires connected to the balun, one to each post, the noise dissipated drastically as did the SW signal.

I left it with one wire connected for some time.

Yesterday I replaced the PVC with a 13 foot fiberglass telescoping pole (Black Widow Crappie pole). While at it, I secured the wire in several places up the galvanized and fiberglass poles.

To my amazement, with a single wire attached to the balun, broadcast AM was everywhere. The entire SW/HF band was polluted with BC AM signals. No shortwave was possible as the overload was overbearing.

With the second wire attached, BCAM overload practically disappeared, but as it was before, so did most of the noise and signal.

I was not able to pull in any SW stations during times when I would normally. One wire on = terrible overload. Two wires on = no overload but also little signal. I was able to hear an 80M conversation between two hams in Southern Utah (about 120 miles from me) - that's it.

The only real change to the antenna system was replacing the PVC with fiberglass, adding a foot or two to the height, and securing the 24 gauge coated wire to the galvanized pipe and fiberglass pole.
I will check today, but I think the wire running up the pole is perhaps causing the problem. It is secured several times up the pole with Velcro.

If this is plausible, why would the 20 foot section of pipe create such an overload with the wire secured to it? Again, with it hanging loose and not touching, the problem was not present.

I am trying to understand what is happening to have a better understanding of the interplay and ways to prevent it from occurring.
 

ultravista

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I am using an RTL-SDR v1.3 dongle. The balun connects direct to the antenna port of the dongle, the wire connected to the balun. The wire runs outside, up the mast, and down to a point in the yard. The wire is coated but secured to the galvanized pipe with Velcro wraps.
 

ridgescan

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I am using an RTL-SDR v1.3 dongle. The balun connects direct to the antenna port of the dongle, the wire connected to the balun. The wire runs outside, up the mast, and down to a point in the yard. The wire is coated but secured to the galvanized pipe with Velcro wraps.
In my opinion, your antenna wire needs either an RF ground or a counterpoise of some kind to work against. If you fed the wire with 50ohm coax the braid could go to RF ground and would clean up noise a bit and protect desired signals. Also the coax would get the wire out and away from RFI sources.
 

ka3jjz

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That pipe might actually be acting as a short - which would account for you losing most of your reception. How is a little tough to judge. However mixing metals like you're doing here (and just securing it with velcro) is never, ever a good idea. Eventually the 2 metals will interact, and may actually cause more interference. You see, sometimes when you bond 2 dissimilar metals,, as the metals corrode over time, they could, in theory, become a very crude diode, which is not what you want here. There are compounds that you can use to prevent this from happening.

As has been mentioned before, your overloading issues are quite understandable, given that these little RTL sticks have next to no front end filtering to help avoid such problems. You should either reduce your gain (you shouldn't need to run it full out in any case), and/or add a filter to block the BCB signals from getting to the stick. There are many such filters available, including from PAR electronics, among others. Either or both may be needed - every setup is different.

Large antennas in an urban area aren't always the best solution, particularly when you're using an el-cheapo SDR that has coverage as wide as the proverbial barn door. Even a 40 or 50 foot random wire might be too much for these little sticks in some cases. If you've got only a small space to work with, I'd consider a loop right off the bat. And you wouldn't need to spend USD500 on a Wellbrook or Pixel. There are many other designs that are a whole lot cheaper.

Mike
 

ultravista

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ka3jjz- will you recommend a loop (non active ?) that may work better than a long wire?

Also, what are your thoughts on a Beverage On the Ground? While I don't understand the concept, a low antenna on an earthen ground, it does sound interesting.

Thank you for helping.

RPK
 

ultravista

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I think it's the galvanized pipe. I split the wire today, pair to single wire, and will run one up the pole and down as a sloper and the second as a ground.
 

ridgescan

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I think it's the galvanized pipe. I split the wire today, pair to single wire, and will run one up the pole and down as a sloper and the second as a ground.
I reread your OP and I see now. Get that receive wire away from the galvanized pipe-there's probably local RFI riding that thing. Here, I try to clear my receive antennas from metal stuff by at least 10' as a general rule. I hope your new configuration works out better for you.
 

ka3jjz

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ka3jjz- will you recommend a loop (non active ?) that may work better than a long wire?

Also, what are your thoughts on a Beverage On the Ground? While I don't understand the concept, a low antenna on an earthen ground, it does sound interesting.

Thank you for helping.

RPK
I'm strictly a cave dweller (condo) so even thinking about a Beverage on the ground (or BOG as it's sometimes used) would, sadly, be out of the picture. This is a true longwire (notice written as one word) type that is mounted very close to, or even on, the ground. All the reports I've seen of folks that use BOGs are that they are pretty lossy, due to them partially being dependent on the ground conductivity, but are also pretty quiet antennas. I kinda doubt you have the space to lay one of those down - remember, a true Beverage is 1 wavelength or more at an operating frequency.

Now loops I've been fiddling with - can't say I'm an expert, but there are several books out there on the subject. Quite apart from the ARRL books, anything by Joe Carr is worth reading. As to what unamplified loops are out there, before anyone can answer this, what bands are you looking to cover? We have a few in the SW only section here...

Loops - The RadioReference Wiki

If you generally stay above 5 Mhz, then Dale's new loop is worth looking at (Dale is/was? a RR member). There are a few from Alpha Antennas that are worth a look as well. You can do a Google search on some of the names that Dale mentions in his writeup. While these antennas are ham-related, don't let that put you off - they will work just fine for listening as well. In addition we've got a few homebrewed designs listed there, if you're fairly handy with tools.

Mike
 

ka3jjz

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This is a distinct possibility for you - and it's WAY less expensive than a Pixel or even a W6LVP loop...

Model HF-315 Portable HF Magnetic Loop Antenna :

Don't fall into the trap of thinking that the signals should be as loud as you hear them on a random wire. Think more in terms of signal to noise ratio. I would much rather listen to a weaker signal that's free from noise than a loud signal that's bothered by some noise source any day, and most DXers will tell you the same thing

Mike
 
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