RFI problems with antron 99

[whitedove]

I have an antron 99 in the yard 100 ft away from the trailer and is about 20 feet in the air. I am using about 130 feet of rg 8x coax cable. I am not using an amp. The radio does 100 watts but I am only using 80 watts. SWR's are good on 10 and 17 meters without a tuner. They are not too bad on 12 and 15 meters. Depending on which band I am on I have terrible RF problems. When I key up and talk my satalite tv. box goes crazy. Sometimes it shuts off or the channels change. Sometimes I have had to reset the box. I tried making an rf choke. I wound 5 turns of the coax cable onto a 4 in. piece of pvc and used tie wraps to secure it. I used tie wraps to secure the coax choke to another piece of pvc to insulate that from the mast. I thought I had the problem fixed but I guess not.

Should I start by upgrading the coax to rg 213u. Would that help?

Should I buy something like the radiowavz or mfj Rf isolation balun?

I would appreciate any help from you Elmers
Thanks
Whitedove

 

[Robb]

Not an 'Elmer', but I have fair idea of what is happening . . .

The problem isn't the coax. The problem is, there is no 'counterpoise' or 'ground plane' for the antenna for each band that you are trying to use it on.

You need to make a 'counterpoise' or 'ground plane' for it. Actually - several. You will need to cut at least two pieces of wire that are 1/4 of a wavelength long - for each band used - and attach them to the base of the antenna. Each of them going in opposite directions from each other.

Example:
2 wires attached to the base of the antenna that are 1/4 wave length for 10m, then another 2 for 12m, 2 for 15m, 2 for 17m, and even 2 for 20m (each 2 wires needs to be 1/4 wave length long for each band).
1/4 of 10m would be 2.5m long
1/4 of 12m would be 3m long
1/4 of 15m would be 3.75m long
1/4 of 17m would be 4.25m long
1/4 of 20m would be 5m long
These are just examples; the real lengths will be more or less than these dimensions.

http://www.youtube.com/watch?v=-qEnBtWV-6c

You can install the antenna at ground level and run these wires radially away from the antenna base. Like the spokes on a bicycle wheel. You will probably need to use an antenna tuner to keep the SWR match @ 50 ohms. It should work well on 10m and 12m, OK on 15m, acceptable on 17m and worse when you get to 20m.

Because there isn't a 'ground plane' or 'counterpoise' as you are using it, the radio wave that is being transmitted on the different bands is using the coax by default as that 'counterpoise'. Not cool. This will bring stray RF into your radio room and create havoc with all electronics.

 

[whitedove]

Thanks Robb I'll do that.

 

[mr_fx]

Because there isn't a 'ground plane' or 'counterpoise' as you are using it, the radio wave that is being transmitted on the different bands is using the coax by default as that 'counterpoise'. Not cool. This will bring stray RF into your radio room and create havoc with all electronics.

I love how cb'ers think that no radials is a good thing... they think I am on idiot for building radials and running a choke... it's so funny they just don;t get it

 

[BOOTY MONSTER]

hey now , i'm a CB'er and i love ground radials ..... wouldn't use a antenna that doesn't use them .... except the GM .
buy why take a step down from my .89

 

[Beetle]

Also, consider the fact that the A99 is designed primarily for CB operation. The fact that your "SWR's" are "good" on other bands doesn't mean much. A dummy load will show low SWR, but it's a lousy antenna.

Try sweeping the A99 with an antenna analyzer that shows both SWR and reactance. I think you'll find some surprising things about the antenna system you have.

Get a decent multiband vertical or make a dipole for the lowest frequency band and feed it with parallel line (window/ladder line); you'll be much happier on the amateur bands.

 

[Marconi]

I agree with Beetle, he has the best solution.

I don't think you want to ground mount your A99. Some A99's are just bad with TVI, and fixing it using radials and a balun, likely won't work. You'll have to try and figure that out first. Maybe install it at a friends place and check it out somewhere else.

IMO, if you're unlucky and the coil inside the matcher is not tinned, soldered, and isolated well by the manufacture, then there's little you can do. You could paint it in Gold and it wouldn't help.

Welcome to the forum, and good luck,

 

[Robb]

I use my Imax 2000 on 10m, 11m, 12m, 15m, and 17m.
Don't even have any radials with it. Sure it would work much better if I did. I have many of the same problems mentioned with it since I don't run any radials. It may not be ideal; but it still works . . .

 

[n0zna]

Yep a99 and imax 2000

Shakeshpere big stick Rad Shack Pogo Stick are good antennas on 10/11/12 but they are known as splatter poles...73 de JW Another question,is it a Sylvania TV?They are known for tvi also...

 

[Marconi]

I use my Imax 2000 on 10m, 11m, 12m, 15m, and 17m.
Don't even have any radials with it. Sure it would work much better if I did. I have many of the same problems mentioned with it since I don't run any radials. It may not be ideal; but it still works . . .

Robb, I don't hear the same complaints about the Imax as I do the A99, so there may be a difference if I'm right that the problem could be inside with the antenna's matching device.

If WD was talking about an Imax, that would be different in my mind, and I might have just past on by, and not mentioned the issues that I've experienced with some A99 myself.

I have heard other operators make similar claims about their good results, like you, using their Imax.

 

[whitedove]

Shakeshpere big stick Rad Shack Pogo Stick are good antennas on 10/11/12 but they are known as splatter poles...73 de JW Another question,is it a Sylvania TV?They are known for tvi also...

The problem is not the tv no problems with the lg tv. The problem is with the directv dvr box.

 

[TonyV225]

I see people do this all the time with mounting those antennas low to the ground. When you trasmit your just blastisting your signal or RF right into telephone a powerlines and wires houses TV antennas ETC.

Get that antenna in the aire and get the groundplane kit or a groundplain kit I dont bother anything with my Antron 99 no matter what band Im on and thats without a lowpass filte inline even.

I have however been having trouble with my inverted V on 75 meters with the amplifiers on but I think its narrowed down to a ground issue.

 

[M0GVZ]

I've just put up an Imax 2000 and had the same problem as the OP. I experienced the worst RFI I ever had. I experienced it as noise on my computer speakers. I put a RF choke inline at the back of the radio and it stopped it. AHA. Basically it uses the co-ax for the missing half of the antenna. It was something which I really should have expected before I started.

Cured it though. First method I tried was 5 turns of RG58 round a 110mm uPVC waste drain pipe as close to the feed point as I could get. At first it didn't work because I stupidly then taped the Co-ax to the ally mast it was being forced to use as a counterpoise. Bringing the co-ax away from that sorted it and at least confirmed the choke was doing what it was supposed to be and the mast was now being used as a counterpoise.
5 turns of RG58 on a 4.25" diameter tube should give you over 4k Ohms choking on the 10m band however air wound chokes are narrow and mostly reactive so can cause problems.

As I've used an Imax 2000 on 15m before with reasonable results, an air wound choke wouldn't really be a solution, giving little choking on 21Mhz and always with the possibility of it actually increasing CM.

However as a RF choke using co-ax wound over a toroid is mostly resistive and gives good choking over a far wider bandwidth I decided to make one. I don't mind winding my own toriods so I made one from a spare FT240-43 mix I had. I used 6 turns of RG58 on a FT240-43 mix toriod. Put it all in a nice little box with a SO-239 chassis mount at the bottom and a short 4" stub of co-ax with a PL259 on to fit to the antenna so it looks all professional and the whole lot cost me about £10 and my time. Testing the RF choke into a dummy load shows > 2k Ohms impedance from 1.6MHz through to about 20MHz and from there to 30MHz is >1k Ohm. I've got the co-ax coming away from the mast its on.

Tested it this afternoon on 10m. First QSO was with an OD5 in Lebanon and I was 5/9 to him with 100W. I also had a QSO with ZS1HL a couple of hours later once I'd permanently put it together. He is 5890 miles from my QTH according to QRZ.com and was running 400W into a 3 element beam.

Some good stuff here about RF chokes.

But as I said, DO NOT tape the co-ax to the mast because you'll just undo everything you've done to stop it.

 

[W5LZ]

How do you check an RF choke into a dummy load?
- 'Doc

 

[MRASSHOLE]

I love how cb'ers think that no radials is a good thing... they think I am on idiot for building radials and running a choke... it's so funny they just don;t get it

I guess you are setting the standard for being a friendly Ham operator....I never forgot where I came from and never will,had many many cb'ers as you say come to me nad say thats why they would get a ham ticket,for fear of being made fun of,and even to the point of being reported......I bet your one of those guys that turn in a new recruit that doesnt comply to the rules perfectly....10-4 good buddy...!