in Transmit Audio
Problem: I have severe RF in my transmit
audio if I use anything other than a direct hand-mic into the front of the
radio. I need to run a W2IHY EQ and a RIGBlaster (the W2IHY box at a minimum
since my mic is a Gold Line Pro with an XLR connector).
I don't have access to an earth ground since I'm in an apartment 3 stories up,
but for the last 4 years, that was never an issue -- I'd never had RF into the
TS-570D(G) that I'd used all that time. Now the Mark V is completely unusable at
any power level over about 40W or so on phone. I've been using it mostly for CW
and a little FSK in the interim, but I'll do anything to get this SSB problem
solved. I'm trying to achieve ESSB audio.
I've tied everything together and run a line to the radiator feed pipe in the
shack, and it made absolutely zero difference. I tied audio ground to the
connector shell on all my mic connections and it made no difference either. On a
dummy load it's mostly clean (still a little something but acceptable for the
moment), but the instant I go over to a live antenna it's so bad at times that
I'm almost completely garbled.
My antennas are dipoles on the rooftop above my head, coax baluns and a W2DU
current balun on each one. Nothing except the radio changed in the last 2
Solution 1: Courtesy of Heil Sound
REMOVING RFI FROM AUDIO INPUTS
Many amateur radio stations today are experiencing terrific RFI (radio Frequency
Interference) that is impeding their audio signals and causing very garbled and
distorted audio. Careful listening of MANY SSB signals on the air today exhibit
RFI - not sometimes enough for their receiving stations to notice as they listen
to a 3" speaker of a transceiver but careful listening in a wideband receiver
with VERY high quality receiving equalizers and studio monitor speakers allow
this slight interference to become VERY annoying. But then there are the signals
that have terrific problems with RF getting into their audio lines and cause all
sorts of problems.
We, here in the Heil Sound lab have discovered a very interesting fact. Most of
the major transceivers today do NOT ground their microphone shields! That's
correct - the mic shields FLOAT! Now wasn't this one of the FIRST things we
learned about building RF transmitters with speech audio sections? GROUND those
shields!! So, we came up with a very simple fix that just about anyone can make
to their rig...don't have to get inside...don't void any
This applies to the 4 and 8 pin Foster (that's the Japanese company that builds
those dang little mic connectors!!) microphone connectors so common on today's
rigs. Plug your Heil (what - you don't have one yet! ) microphone cable into the
front panel of the transceiver.
Remove the two small #4 Phillips head screws and the cable clamp they hold. Then
remove the tiny Phillips head screw that holds the rest of the metal sleeve.
Slide that back onto the mic cable. Now...cut off the end of a resistor or get a
#20 solid tinned wire about 3" long. Locate the mic pin that has the shield of
the mic cable soldered to it. With a small iron, carefully solder this solid
wire to that shield and pin. Bring the sleeve back up the cable and attach to
the connector with the small screw. This leaves the solid wire coming out the
back of the connector. Replace the cable clamp and as you do that, tightly wrap
that solid wire around one of the #4 Phillips head screws and tighten the clamp
assembly very well.
What you have accomplished is grounded the shield to the transceivers chassis
ground through the ring on the mic connector. (Make sure that ring is tight).
This has been a big help to many stations with RFI problems and should help you
clean up your signal.
Solution 2: There are some things you could try out: - Your problem seems to be
caused by improper HF grounding and relatively high RF fields in the shack. Try
to improve the grounding as the first step. A radiator pipe is practically
useless as HF ground which is a completely different animal compared to DC
ground. Use a counterpoise as grounding system on the radio system. A length of
tuned wire laying on the floor in the apartment could work. You need one wire
length for each band. It is of paramount importance to have a perfect grounding
system for all equipment for an ESSB station.
Alternatively you can try the MFJ artificial ground match box. - Use quality
audio isolation transformers with RFI decoupling to block HF in all lines from
the microphone to the radio (it may also be necessary between the different ESSB
boxes- maybe that is already the case with the -W3IHY EQ). The W2IHY MURF-box is
an excellent item. I have built one myself in a small metal box. - Study the
NU9N information pages about ESSB. There you will have a lot of ideas on how to
battle RFI and build your ESSB station.
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