Wednesday, January 4, 2017

The ground is not beneath your feet

Yet another article about proper grounding (yawn)

It seems as though one of the biggest misunderstandings in amateur radio is the issue of "grounding". I have probably read more than a dozen articles about grounding and sprinkled a little from each regarding setting up my station.  But there always seems to be more to learn.  This time I learned more about electrical grounding rather than RF grounding.


I generally try and send my CQ calls at 5 watts RF output or less. If I receive a really poor signal report from the answering station I'll raise my power if I'm able to 20-40w to give them 6-12 more dB to make it more pleasant for them to work me.  Propagation has been really poor for me over the past few weeks and I've found myself getting lots of 339, 459 reports etc. and I've been using the Eagle to bump the power into QRO range of up to 80 watts sometimes (gasp).  

However whenever I raised my power in such a situation my TenTec Eagle would behave oddly...

After I'd finish keying there would be a brief audio drop and sometimes a pop as the audio came back.  I thought an under voltage situation was occurring so I measured the voltage from the power supply to the rig while transmitting into a dummy load.  The voltage only dropped from 13.8v down to 13.6v so that didn't seem to be the problem.  Even transmitting QRO levels into the dummy load sometimes resulted in the audio pop but it was always after I un-keyed, never during the actual transmission.

I was perplexed.  So I put my question to the TenTec Eagle Yahoo Group.  Over the past year I have learned more from the technical discussion in that group than pretty much any other single forum...  A frequent contributor to the TenTec Eagle Yahoo Group, Bob, K4TAX, answered my question:
Yes, the Eagle chassis is "floating up" that is to say the DC negative is not really at zero volts as current increases with higher power.   I suggest a dedicated ground from the Eagle chassis ground terminal to the power supply ground terminal.  For all of my ground jumpers I use #10 AGW auto primary wire to which I crimp and solder a proper lug to each end...
I did already have the station ground connected to the AC service ground via a fused connection but it was a small guage wire and apparently insufficient to tie the radio back to the power supply ground.  So what did this mean?  Bob, K4TAX followed up with an email a couple days later to see if I'd resolved my issue...
 Many, I find, believe the DC Negative is adequate between the radio and power supply.   In as much as the radio ground system internally has in effect two ground systems, one being for digital ground and one being for analog ground, we commonly find that the resistance between the power supply and the analog ground does allow the radio to float up above zero volts when in transmit.  To test for this condition, measure the voltage between the power supply ground and the ground terminal on the radio.   Put the radio in CW and key down.  The voltage should be less than 0.25 VDC.   If it is greater than this, the voltage drop is caused by the resistance in the DC power cable or the ground method used for the station.    For this reason it is strongly suggest one have a dedicated ground connection between the radio and the station power supply.  
When I performed this measurement I saw that the DC negative between the radio and the station ground was in fact "floating up" by more than 0.5 VDC.  When I shortened the DC cable to only 18" between the power supply and the rig that resolved the float but the proper answer was addressing my DC electrical ground.

Station and A.C. Electrical Service Grounding

  1. If not already in place, add Chassis Ground terminal to your Power Supply, and internally bond chassis ground to D.C. negative terminal.
  2. Connect all station equipment chassis grounds direclty to P/S chassis ground. See Figure 1 below.
  3. P/S MUST have three wire A.C. connector, plugged into mating receptacle with ground tied back to A.C. Main Service Entrance ground.
  4. The P/S chassis ground is your Station ground. The A.C Power connector ground bonds to your A.C. Main Service ground.

Figure 1 below depicts ground wire from each piece of equipment is tied back to the Power Supply Chassis Ground.

The Power Supply MUST have Service Ground on A.C.Connector to complete an effective Station AND Service Ground.

The fix

My station grounding was somewhat haphazard.  As I'd added equipment I'd added ground straps between new components and whatever was nearby.  I had different gauge wires, and sometimes used RF straps for DC grounding and... well it was a mess.  Armed with new knowledge from Bob I went to Home Depot and purchased 50ft of #10 AWG with #10 AWG terminal eyes and #10 AWG butt connectors.

I cut a 6ft piece of the #10 AWG wire and every 18” along the length solder/spliced in a 10# AWG wire adding a butt connector resulting in 18” jumpers that allowed each piece of equipment to be attached via a jumper with the butt connector. Each jumper had a male butt connector on one end and a terminal connector to connect it to station grounds at the other.  That allows me to easily move equipment around the station ground without unscrewing the ground lugs.

I now have all the radios, tuner, switches and power supply bonded together properly. I also bonded to the chassis ground of my filtered power strip that feeds AC to all the components.

Also at Bob's recommendation I disconnected my station from the separate ground wire that ran to my outdoor ground rods.  My outdoor OCF Dipole comes back through an Alpha Delta spark arrestor that still ties into that ground rod system which is also tied into the house service entrance ground.  

The result

I'm happier than a slinky on an escalator... Ok I've used that one before but it's applicable again.
  1. First, there is no longer a rats nest of ground wires running between everything.  Ok, points for neatness.
  2. I can individually disconnect a component without removing the ground wire through the removable butt connector.  Points for not fighting with the ground lugs when I need to pull a component or re-configure the station.
  3. My Eagle can run QRO up to 100 watts out if required with no DC floating issues.
  4. Here's the phenomenal bit... the band noise at my station is now One S-units lower on 40m and 20m and Three S-units lower on 30m.  Honestly I have a hard time believing that re-working the DC ground and disconnecting from the long outside ground wire made that big a difference in my noise levels but it has.


There is so much to learn in this hobby.  My "aha" moments just keep coming.

So if you're like me and didn't know that your radio may have separate Negative VDC voltages between its power and its chassis and what the ramifications could be if they were unmatched, well now you know.  Just a few Ohms difference between the power supply negative ground and radio chassis ground can have side effects inside your radio.  You may not even know there are problems brewing inside there, so ground that station properly for VDC!

Also, if you're running a long ground wire to your station separate from your AC mains safety ground then you're creating a ground loop of at least a few Ohms that gonna cause problems.  

I am not saying that you shouldn't (if your run to ground is short enough) run a ground for an antenna grounding system.  But that is RF grounding and its a very different topic.

That's all for now...

So get rid of that long ground wire, properly ground your station to your power supply and make proper use of your AC mains safety ground.

Richard AA4OO

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