I am posting this once again for those having RFI problems and believing
that it is a problem with their transceiver.
I apologize for the lengthiness.
SDRâs, You and RFI
I have spent the last three years investigating "Special Grounding"
techniques.
What I'm going to suggest here is a look at your entire grounding system.
I'm talking about RF, AC, Telephone, Cable TV grounding and DC grounding.
AC Grounding:
1. All 115v power for your HF/VHF equipment should come from one receptacle.
Failure
to do this may lead to ground loops via the green wire that runs through out
your home.
This receptacle should not shared with other appliances in your home. The
receptacle I use is a dedicated circuit for the clothes washing machine.
2. Take a look at your electrical service panel. There is a very heavy gauge
wire running
from the ground bus outdoors to an 8' copper grounding rod. Hopefully this
wire is copper
and not aluminum. If it is aluminum have it replaced with copper.
Assuming that the grounding wire is copper, disconnect the ground wire,
clean it and
the grounding rod with a wire brush and/or sand paper. Reconnect the wire to
the
grounding rod with a suitable type clamp. I use a very large split-bolt.
Tape it and
make it water tight.
You will also note that the telephone people and the cable people may have
terminated
their equipment signal ground on your AC ground. Install a separate
grounding rod for
this equipment, tape it and make water tight. These are special purpose
grounds and should be treated separately.
Note: The NEC is concerned with grounding for safety only. They could care
less about RF.
This next topic is my favorite, RF Grounding. First a little history.
My antenna, a Sterba Curtain, is directly (about 10') over the top of my
home. On 160m, 75m and 40m I run a full 1000 watts with no RFI or TVI. I also
use a ton of sound reinforcement equipment at my HF operating position also.
Your station HF/VHF station should have what is call a "single point" RF
ground. I'll explain.
Lets say that your RF chain is as follows:
1. Transceiver
2 Amplifier
3. Antenna Tuner
4. RF Grounding Rod
Under the above conditions, there should only be one wire going from the
grounding lug on the back of the antenna tuner out to the grounding rod. Do
not
ground each piece of equipment to a central point and then out to the
grounding rod. Each piece of equipment is already RF grounded through the
inter
connecting equipment jumper coax shields. Failure to ignore the above may
result
in ground loops.
The RF ground wire I use is a length of RG-8. Only the center conductor is
terminated at the TT-1251 tuner. Outdoors at my RF grounding tie point the
center conductor is shorted to the shield. this will effectively drain any RF
to
the Star RF Grounding Counterpoise System.
If your antenna is a multi-band dipole. A dipole is a balanced antenna, if
you are feeding the dipole with unbalanced coax the shield of your coax, and
your entire station, is acting as the other half of the antenna system.
Installation of a 1:1 Balanced to Unbalanced Current Balun at the antenna feed
point will stop return currents on the coax shield and gracefully make the
transition from a balanced antenna to an unbalanced system. If you are running
a
vertical antenna install a Current Balun Kit (as sold by Polomar-Engineering)
at the feed point.
>From Radio Works, purchase a 50ohm bal to 50ohm unbal Current Balun (B1-5K
cost $34). This device installs at the feed point of the dipole. Also purchase
a T-4 Line Isolator, this device installs between your rig and the
amplifier.
I recommend the following RF chain:
1. Transceiver (Orion, TS-950SDX, IC-756 Proll)
2. T-4 Line Isolator (from Radio Works)
3. Amplifier (AL-80B) Donât forget to put a toroid on the keying line.
4. Tuner (TT-238B)
5. TT-1251(Counterpoise RF tuner from Ten-Tec)
6. Star RF Grounding system (detailed construction drawings are available
upon request)
Note: An RF Grounding system will help with lightning protection, but a
Grounding system for lightning protection will help very little with RF
Grounding. Donât confuse the two.
I have probably furnished more information than you want. But, to address
some issues with SDRâs and unusual operations, it was necessary.
I can hear it nowââguys saying â I never had to do that with my old
rigâ
..what a bunch of BSââââ. Wellâ. welcome to the world of SDRâs.
,
Have fun
John / N0KHQ / St. Louis
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