RF in the shack
OK Guys, I have an radioworks T4 isolator between the radio and the amp, I have one T4 between the amp and the tuner and I have a T4G between the tuner and the antenna switch, When I use the amp on some bands it drives my answering machine nuts, it turns my computer monitor on and off, and I can be heard in my TV and stereo speakers. I have 2 ground rods, I am using rg8 sheild for ground wire. I am out of ideas.
Any help out there??
I have found the advice in http://audiosystemsgroup.com/PAARA-RFI-2011.pdf and http://audiosystemsgroup.com/RFI-Ham.pdf extremely helpful in eliminating RFI in my house.
I would try winding 12 turns of the telephone cable to the answering machine around a 2.4" diameter #31 toroid as discussed on page 20 of RFI Ham pdf link. For the computer monitor try a choke on the power cord feeding the monitor.
Good news! You can take out the two plain T-4 isolators. Besides grounding the radio to the same ground as the amplifier defeats the isolator in between anyhow.
Without knowing anything else about your installation the standard things to try are:
-Run lower power
-Move the antenna further from the shack
-Re-orient the antenna
-What rig, what amp, what power causes problems, Band, Antenna type/brand; distance from shack, height, orientation?
Author of: Mr. Fred, Nuke This Forum (Danger Close)
I don't know why anyone would ever tell someone to put isolators inside the shack, let alone between pieces of gear in the shack.
Originally Posted by WD8BXS
The last thing anyone should ever want to do is place an isolator between equipment on the desk.
If you have a properly designed and installed antenna system, the ground should be meaningless for RFI.
When I use the amp on some bands it drives my answering machine nuts, it turns my computer monitor on and off, and I can be heard in my TV and stereo speakers. I have 2 ground rods, I am using rg8 sheild for ground wire. I am out of ideas.
What antenna do you have, and how far from the house is it? Some antenna are very prone to common mode currents, and some antennas are too close to houses. The problem almost certainly is with the antenna system.
Three isolators? That's insane.
Originally Posted by WD8BXS
There are too many factors left out of your post. In addition to what Tom has asked, I would add the following questions:
What's the length of the "ground" wire between the equipment and the ground rods.
What band(s) does the problem occur on?
Given you initial post, I'd lean towards a proximity issue. I run a KW here with 5 wire antennas and I have little to no issues. About the only things I bother are computer speakers on the 2 main computers on the main floor, and that depends on whether I'm on 40m or 75m.
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Chuck, I also wouldn't use isolators anywhere inside the shack or between equipment.
The T4G alone might do something, used outside (I have two of them, they're both outside) before the coax comes inside the shack. Mine are just bonded directly to 8' ground rods that each have some wire radials spread out around them and then buried by soil behind the bushes. By "bonded directly to," I mean there isn't any braid or wire between the T4G strap connection and the ground -- they're bolted directly.
I did this for 80m and 160m only, as didn't need them anywhere else. I think the reason they helped slightly on the lower bands is my antennas, while 75' from the shack, are still really close in terms of wavelength and the coaxial feedlines can easily couple to the antennas on those bands, almost no matter how they're run.
What you describe isn't so much "RF in the shack" (I don't think), but rather "RF in the house!" and getting into appliances that aren't intentional receivers. Really common stuff. I've always found "distance" helps more than almost anything else (keeping antennas as far away from the house as possible), but also treating each interference receptor case by case usually helps until you get some new appliance and have to do it again.
A government which robs Peter to pay Paul can always depend on the support of Paul.
-- George Bernard Shaw
Another salesman happy to sell these isolators by the dozen?
Originally Posted by w8ji
We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths. -- Walt Disney
OK I am running a 756 pro III, a Dentron MLA 2500, am Dentron MT-3000 tuner. Trouble only occurs when using the amp. As you could see from the first picture, that is what was recommended on the radio works site. Her is a sketch of my shack. It is in a basement under my garage, metal decking above me under the cement garage floor. concrete block walls. 40 feet from the dipoles, which are 50 feet high. about 30 feet from the outside wall to the vertical. 40 meters gets the TV and answering machine, 20 and 10 meters gets the computer monitor.
There is a lot missing from the drawing, but there are two causes of common mode currents that affect consumer gear.
The first cause is lack of a proper balun where a balanced to unbalanced junction occurs. This would be where coax interfaces with a not perfectly unbalanced system. An example would be where coax interfaces to a dipole antenna, or to a vertical with a small ground system. For example a vertical with four radials can have pretty high common mode currents, as can coax connected to a dipole. Another source is an in perfect balun in a tuner that feeds balanced line.
The second cause is other conductors or consumer devices in the near field of an antenna. That would be within 1/2 wave or so, depending on power levels, the devices, and so on.
I'm not sure which (or both) problem you have, but NEITHER problem is fixed by a ground in the shack, or isolators in the shack. As a matter of fact as a designer of amplifiers for 35 years, I would NEVER tell any customer to install isolators inside the shack wiring. If that does anything, it actually does exactly the opposite of what is needed!!!! I repeatedly tell people to remove isolators in the shack between pieces of gear, because it is never good and never what is needed.
So what feedlines are you using, and how are they routed into the house??
I am using RG-8 I have one length of it running outside to an antenna switch right below the dipoles. all of the antenna's are fed from there. I have a balun on the 75 meter dipole. I have a coaxial choke at the feed point of the MFJ-1798 vertical. It needs no radials. I also have coaxial chokes at the antenna switch for all three of the antennas. So you are saying that the pic from radio works is a bunch of crap? I have the power cord on the amp wrapped around a big ferrite core from an old TV (someone suggested that). I updated the pic showing the coax route. I have a ground buss and all grounds connect to it.
So you are saying to lose all of the isolators in the shack and place then before the antenna switch outside?
The Mystery antenna does not have any baluns in it. It has rg8x connecting directly to twin lead, should I have some sort of balun there, if so , what kind do you recommend?
I really appreciate all of your input.