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Ham Shack Grounding For Digimodes

After many years of selling CAT control and Digimode interfaces, we have noted that poor grounding is the cause of many issues when connecting your PC to your Radio either for CAT control or when you come to try Digital Mode operation.

 

I have based this quick guide around my own experience and excellent articles from 3rd party websites who also offer sound advice on this subject. I have linked these external resources within this page and in a list at the end.

This guide is not intended to be a reference article on shack grounding. The aim is to to give you a few pointers with regard to improving your shack grounding for Digimode operation and some excellent resource pages to go to if you need more information.

 

Lets lay out exactly what we are achieving with a proper grounding regime in your shack. (lifted and summarised from the excellent ARRL Grounding guide)

  1.  Safety ground - ie tying the chassis of your equipment to ground to protect YOU from an electrical shock should a live wire or component inside the equipment comes loose and connect with the chassis.

  2. Lightening ground - Allowing for the safe dissipation of energy to ground should your antenna or cabling get struck or voltage be induced into the system.

  3. RF Ground - This is very much depending on your antenna design. For example a quarter wave vertical antenna is driven against ground and so a good low impedance path to physical ground is essential for an efficient antenna. Your grounding system may need to consist of many ground radials if the antenna is short with respect to its wavelength. Antennas such as a dipole are less reliant on ground. But these are prone to common mode currents on your feedline. Common mode RF can then come down the outer of your coax re-radiating in your shack. This can cause all sorts of local RFI issues.


On top of the critical safety elements of grounding, issues in the shack can be compounded by poor or non-existent earthing. These can include ground loops in the system, leaking voltages from power supplies and RFI making it back into your shack. These issues can manifest in many forms

  • RF Pickup in the shack when transmitting including getting "shock and tingles" from equipment.

  • Distorted transmit audio or mains frequency related harmonics (Hum) in receive signals and waterfalls

  • PC issues such as mouse/trackpad instability, distorted monitor pictures, data corruption

  • Inability to get a good or consistent match on your antenna despite you having a tuner

  • CAT Control dropouts or software crashing/hanging typically when transmitting

  • PSU instability causing potential poor regulation on your radio PSU

  • The list goes on.........................


The first challenge is that you really should have a proper ground rod with a short run of heavy duty cable to your main shack ground point. Then all equipment should be grounded to to that common point. And when I say all equipment, this MUST include your PC. It now forms part of your shack.

A typical grounding system diagram is below.

Shack Grounding.JPG

Now I am fully aware that for many hams, it is simply impossible for you to install a proper ground in your shack. You may live in an apartment for example.  In these cases hams often rely on the power system ground in the room the shack is located and use antennas that are not reliant on a proper physical ground. But in these cases, you are much more prone to common-mode current issues and RFI in your shack. I have had enquiries from some hams where the antenna is actually in the shack and then wonder why they have problems.

But the moral of the story is if you don't have a proper external ground system and relying on "main supply earth", you are simply inviting RFI and other problems and will have to try to mitigate the issue. 

 

You will note in the diagram above, your PC now forms part of your shack system and must be grounded.

 

Grounding your PC is not always straightforward. Most desktop PCs use a Class 1 internal PSU. The PC chassis will be at mains supply ground by nature of the class 1 PSU being bolted to the PC case. You can normally find a screw or stud on the PC chassis to run a ground wire to the main shack common ground point.

Laptop PSU.JPG

However, laptop PCs can be more of a challenge. Often they have double-insulated Class 2 PSUs with no ground connection from the mains supply side. On double-insulated PSUs, a Y Rated capacitor is normally wired from the mains neutral to the negative output rail for EMC suppression purposes. This can have the effect of creating a small amount of leakage from the AC to the DC side of the power supply. This can have the effect or imposing an AC voltage on top of the DC power rail to the laptop. If your system is not correctly grounded, this can lead to unpredictable outcomes.


For example on our test Dell laptop, the power pack has 45v AC on the DC output jack with respect to the shack ground. This AC component can cause errors on the USB cable data and CAT control data if not dealt with. I have seen PTT relay chatter at 50Hz due to this problem.


Finding a place to ground a modern laptop you may think is not easy. If you are lucky, you might get on a serial port or VGA securing stud but modern netbooks often do not have that luxury.

USB Grounding Cable.JPG

However, one option for grounding a laptop or PC is to use a USB Grounding lead. This will connect the screen/0v line of a USB Plug to a crocodile clip or lug which you can attach to your station common ground point. Pop one of these into a spare USB port and then to your station earth and they can work wonders especially if a "proper ground" is not possible. These are available from eBay and Amazon but most folk have a spare USB cable to cut up and so they are really easy to make in your shack. If you make your own, check you are connecting to the 0v line and cable screen. Don’t try to ground the data lines or +5v !!

So my advice is that if you can ground your PC chassis, to your main shack ground point then it is a good idea to do so. If you have a less than optimal shack ground system or cannot ground your PC, then lady luck and a bag full of clamp-on ferrites to attempt to stop common-mode RF may have to be your friend.

But ultimately, referring to item 1 on the ARRL Grounding list. You
MUST have a safety ground.
 

"Safety ground - ie tying the chassis of your equipment to ground to protect YOU from an electrical shock should a live wire (component) inside the equipment comes loose and connects with the chassis"

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