Bhi Ltd
PO Box 318, Burgess Hill, RH15 9NR England.
Tel: +44 (0)1444 870333 Fax: +44 (0)845 217 9936
info@bhi-ltd.com, www.bhi-ltd.com
Ground Breaker
In all but a few cases, you can put a radio system together with all your wanted ‘add-ons’ and it works
without any problem. However, there are a few cases in which problems are experienced especially
with the received audio in ‘add-on’ equipment. These problems tend to be based on RF breakthrough
or Earth currents. In either case it can be found that, when the transceiver is in transmit mode (keyed),
the operator can hear a buzz in the speaker or their own distorted voice coming out of the speaker(s).
There are many reasons why this may happen, but the two main suspects are:
a) A poorly matched antenna which results in RF being reflected back into the radio room.
b) A difference in Ground currents between pieces of equipment. This can be caused by the above
problem or other items of equipment not sitting at the same ground potential.
Most manufacturers take great pains as to point out the necessity for a good grounding system with a
central point to which all grounds are attached. This is also a topic covered in many of the Amateur
handbooks (try the ARRL Handbook Section 28, regarding station installation), so we’ll not go into this
too much, just to say that if you experience breakthrough problems your first port of call should be to
read the information that’s already out there, it could save you money and a lot of heartache.
Having made the above statements, the author as a seasoned engineer in Communications and Radar
systems, even with all the precautions taken to make sure that the systems are properly grounded can
lead to earth loops with the consequence of noise being seen on some module or other.
If all else fails
So you’ve tried providing a better ground system, wrapping the audio leads round ferrite rings, clamping
ferrite beads onto the cables, running your systems up on to different power supplies, checking the
connections etc.
The ground breaker is possibly the final solution, in which you totally isolate the grounds your ancillary
equipment from those of the radio system.
The units come in various impedances covering all the main values (10 k Ohm, 600 Ohm and 8 Ohm)
currently used in many audio systems.
Document: HBA28-80X Issue: 1 Date: 12-01-2018
Ground Breaker Assembly
Type
Maximum power
8 Ohm Mono
500mW
600 Ohm Mono
100mW
10 k Ohm Mono
100mW
8 Ohm Stereo
500mW/Channel
600 Ohm Stereo
100mW/Channel
10 k Ohm Stereo
100mW/Channel
Installation
The Ground Breaker is simple to install. Simply plug the unit into the appropriate socket on your
Receiver/transceiver and then plug the audio apparatus into the socket on the Ground Breaker. It
should be noted that the unit works both ways round the radio can be connected to the socket and the
audio apparatus can be connected to the plug.
Try to keep the leads as short as possible to minimise and other airborne RF pickup.
Balanced to Unbalanced audio systems
Most audio amplifiers used in radios are Class A or AB. They normally have a single ended (unbalanced
output that works against ground, however, recently some manufacturers have started using balanced
audio amplifiers and Class D (switch mode) amplifiers. These present a different problem as most audio
ancillary products on the market (unless they are for professional audio) use unbalanced inputs.
The Ground breaker can be used to isolate the balanced audio output of the set and allow the ancillary
unbalanced input to be unaffected.
Maximum Power Handling
The Ground Breaker, does have limits to its power handling. The 600 Ohm and 10k Ohm devices are
capable of handling the normal audio levels that can be found in most, if not all, audio systems. The 8
Ohm device is only meant to be used at powers up to 0.5 Watts. This is meant to allow interfacing to
most bhi audio products and not meant for the transfer of power into un-powered speaker units.
Document: HBA28-80X 2
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