[Orion] SDR’s, You and RFI - Real Long

[N0KHQ at aol.com]

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.
 
 
SDR’s, 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) Don’t 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. Don’t confuse the  two.

I have probably furnished more information than you want. But, to  address 
some issues with SDR’s and unusual operations, it was necessary.  

I can hear it now……guys saying “ I never had to do that with my old  rig…
..what a bunch of BS”………. Well…. welcome to the world of SDR’s.
,  

Have fun


John / N0KHQ / St. Louis