Counterpoise......

[RolandSWL]

Hi All,

I have a quick technical question. I am using two Alpha-Delta slopers in an inverted V configuration. I can't say I'm particularly thrilled with this arrangement.

I'm using a drake R8A with this antenna system. Seems I'm picking up more noise than usable signal.

I spoke with a Ham at my job and he though that the antennas were designed to be used separately and with a counterpoise.

Could this be why the crappy reception?

I've gone around the house hunting down and eliminating RFI with a Sony ICF-7600G. The plasma T.V. is one of the worst offenders and an electronic aquarium lamp ballast a surprising second.

Any thoughts?

Thanks, Roland.........

[KA0HCP]

What band is your antenna intended to operate on?  Have you modified it from original?

How much of a Vee angle do you have?

Vertical antennas tend to be noisier than horizontal antennas, but that varies with conditions and time of day.

IMO it is always worthwhile to have a vertical antenna for comparison to ones horizontal antennas.

Neither horizontal nor vertical antennas are 'better' than the other.  Each have their strengths and weaknesses.  It really depends on what your operating goals are.

[KM1H]

A full sloper (half wave) does not need a counterpoise or ground system and can be used as a vee or horizontal. Its strictly a half wave dipole.

A half sloper is 1/4 wave of wire and meant to work with the coax shield attached to a tower leg. These are often hard to get working properly since every tower is different. There has been a lot written on the subject.

Now, the A-D SWL Sloper is a 1/4 wave and getting it to work well on any band is a big question mark. Did you follow the install instructions? I think not.

http://www.alphadeltacom.com/dxswlii.htm

[WU2D]

Yes try the half sloper per the directions but I doubt that it will make much difference in the noise pickup situation.

Sounds like you are running the two antennas as a conventional inverted Vee. It is important to get good balance at the feed and decouple "house" noise on the feedline from coupling up and exciting the antenna. For reception, besides a broadband 1:1 balun, I would try 5 ferrites spaced every 6 inches down from the feedpoint. Use double shielded coax like LMR-240 or RG-223.

Another trick is to terminate the ends of the sloped ends with 680 Ohm terminations and wires to a pair of ground rods. This will form a sloped VEE beam which will be broadbanded, quiet and directional.

Mike WU2D

[Jeff W9GY]

On the noise scale of 1 - 10, I'd say a plasma TV is an 11.  "Off" is about the best mode for one of those RFI-makers and since it's yours (and not your neighbor's) you can control it's use.  No way to effectively shield the thing except putting it in a complete farady cage --- but then it would be a little hard to view.   

[WU2D]

Well at least slip a few magic beads onto every cord that is attached to the Plasma set - AC, Audio, Video - whatever.

Get a BIG BAG of clamp on beads. http://www.ebay.com/itm/10-LARGE-Clamp-On-Ferrite-EMI-RFI-Suppressors-/290701363563?pt=US_Portable_AM_FM_Radios&hash=item43af26c96b#ht_500wt_1413

Change out any noisy dimmers. I changed mine to Lutrons.

Mike WU2D

[K5UJ]

Well at least slip a few magic beads onto every cord that is attached to the Plasma set - AC, Audio, Video - whatever.

From what I have read, that doesn't work.   The RF radiated by the plasma TV is through the screen.  IOW the screen is like a giant panel antenna.  You'd have to put the whole thing in a faraday cage and view the screen through wire mesh.   Which means the only thing to do with plasma TVs is take them out back and blow them full of buckshot holes, or persuade the TV owner to accept the gift of a free equivalent LCD set in exchange for the Plasma (then blow it full of holes),  or live with it using RF phase shifting nulling boxes which have their limits and are a PITA to set up, or move to some property where the land is cheap enough to make buying a buffer zone affordable (I've heard you need around 500 feet in all directions to be free from most imported crap RF noise).  

After swimming in noise here in town I'll tell you that moving is the only solution for a lot of this but all that may do is buy you time.

[KM1H]

The magic ferrite these days is the 31 mix and in the FT240 size, Fair-Rite 2631803802. Wrap as many turns as possible of the power cord or RG-6 thru it as close to the equipment as possible.

I dont own a plasma TV but its worked on older and newer types plus cable modems and other crud generators.

Silence doesnt come cheap, $6.94 a pop at Mouser in 1-99 qty.

For RG-213 size cables use #2631102002 slip on beads, those are $1.65 at Mouser in 10-49 qty.

[WU2D]

Plasma screens must meet FCC Part 15 Class B standards for EMI. To do this they use a Faraday screen as you describe. It is built into the front panel filter layer and is usually a deposited screen mesh.

[RolandSWL]

Thank you to all who replied to my question. The antenna in this configuration was used

for nearly twenty years at another location with a much lower noise level. Considering it's 

age, there could be issues with corrosion at any number of electrical connections.

Did I install it per the A/D instructions? Clearly not. The slope angle is quite shallow and

the elements are 90degrees apart, not the customary 180 degrees for an inverted V.

I'm going to move the feed point 50 feet away from the house, clean up all the electrical

connections, increase the height and separate into 2 antennas with a counterpoise each.

Does anyone have any experience with magnetic balun antennas?

I need something not more than 60feet long with good wideband characteristics.

Also, I have put good quality ferrite beads on anything I think generates noise. I'm hoping

that moving the antennas away from the house will reduce the noise I'm experiencing.

Thanks, Roland

[WU2D]

You have not mentioned loops. Have you tried a full sized 40 meter loop? Loops are quiet.

But for covering the whole band on RX, single turn coax loops are probably unbeatable in your situation. Made smaller than a wavelength in circumference at the highest frequency, and fed with a BROADBAND 1:4 or 1: 9 step up balun, the loops very low resistance will be stepped up to something decent for a coax match. These antennas are strictly for receive and cover 100 kHz to 30 MHz. They are inferior to a tuned dipole in gain but with the addition of a modest amplifier, they become very effective. 20 feet or 5 ft on a side in a diamond shape with a small rotator located away from the house will be effective. The antenna is directional, in a figure 8 pattern, especially at lower frequencies. Ground mounting produces high angle pickup, higher mounting receives lower angles.

[RolandSWL]

Hi WU2D,

You just jogged my memory. I did use this arrangement as a sort of loop minus the balun at my prior location. It more resembled a proper inverted V with a wire connecting the low ends. More like a top fed triangle. This may also have caused the antenna to be more quiet.

Thanks, Roland.....

[WU2D]

Just for an experiment and because I needed some outdoor time (not doing yard work), I ran 100 feet of coax out to the woods and hauled up a full sized 80M horizontal loop made from thin copperweld (275 feet). This was just an experimental whim. The antenna was a a bit off on the match at just over 2:1 at 3.6 MHz but was resonant. I got it up about 20 to 25 feet in 5 trees in sort of a pentagon shape. I had an old 4:1 ferrite core balun so I installed that and the VSWR went down to 1.4:1 and she broadened out.

Tonight on a very noisy 80M band, I used it to check in to the Old Military Radio Net. Not only was to quieter than my main station antenna, a 125 ft Inverted L which is fed at my bulkhead by a remote tuner, it gave better signal reports on the closer stations. One station was in Atlanta using an ARC-5 and I could only copy him only on the loop.

Now here is the surprise, It tunes below 1.8:1 on 40M, below 1.6:1 on 20M and 1.8:1 on 15M and I did not try 10M. And it compares RX signal strength wise to the inverted L with tuner on those bands, slightly lower on some signals and slightly higher on others, but in every case lower noise by a big factor. Of course location may be important in terms of noise, as it is away from the house. Oh and I checked the shortwave bands as well and it works gangbusters. So there must be some magic with a loop and a 1:4 balun which allows it to act as a broad banded antenna. So do try a 40M loop and a 4:1 balun.

Mike WU2D