On 8/3/2020 6:58 PM, Ron Manfredi wrote:
I tried both an amplified Motorola speaker and a small MFJ unit, but
when using SSB (10-15 Watts) at home into a beam or into a dummy load I
can hear myself quite clearly in the speaker, so RF is getting in somehow.
Powered speakers have a power amplifier built in, which are notorious
for RF susceptibility. The causes are typically poor shielding and/or
Pin One Problems, but things we do wrong (or fail to do) in the shack or
with our antennas can put lots of RF into a powered speaker, making it
more likely for RFI to occur. Motorola products are generally designed
for UHF 2-way applications, and are unlikely to have been designed for
use around HF transmitting antennas.
What antenna system are you using? If it's some form of end-fed wire
ending in the shack, does it have a counterpoise? It should. If up in
the air with a feedline, does it have a serious common mode choke at the
feedpoint? How is your station bonded? How is it grounded?
Station grounding and bonding is covered here.
http://k9yc.com/GroundingAndAudio.pdf
RFI is covered here. The chokes recommended for killing noise would also
appropriate for cables feeding the speaker (both power and audio).
http://k9yc.com/KillingReceiveNoise.pdf
Transmitting chokes are covered here. http://k9yc.com/2018Cookbook.pdf
73, Jim K9YC
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