We have found a "workaround" to Sparkles VHF woes rather than a definitive solution.
As in most running sores the causes and thus solutions became multi factorial---
Problems in operation
1 VERY poor range.
2 Interference from fuel pump operation and engine operation.
3 At about 200 yds transmitted speech became TOTALLY unintelligible.
Tried and failed fixes
1 Chokes on fuel pump feed.
2 Voltage smoothing
3 Separate motor bike battery. (THIS solution DID work), but became a pain ref charging
because on my craft the intercom is on all the time, and VHF when used on Tx uses a goodly current.
I decided NOW Id found good Tx and Rx WAS possible, then a less complex solution WAS perhaps available somehow.
MY system (removed and re-used from KingFisher) has TWO head phones with adjustable ear piece volumes, and sponge covered mikes,
which are connected all the time. The speech volumes can be adjusted at the dash top, which has the PTT button, as the VHF mike is no longer used. This intercom is spliced into the VHF system, which WAS connected to OLD aerial connections via Co-ax to a new aerial which folded.
Work around----->
1 Old aerial wire replaced as it was feared the co-ax was broken due to old fashioned tight bend in wire.
2 All connections cleaned up, but no problems found.
3 Aerial moved to top of duct via gentle folding co ax mount, instead of tight crimp bend from engine hull area. ( its also raised 2 ft)
4 SEPARATE feed from the battery taken off battery clamps
5 Feed to front of craft, taken down OPPOSITE side of hull to general craft wiring via gently twisted 40 amp new wires.
6 Switch on/off via a spare "Ign Switch" and warning RED light to avoid inadvertently leaving ON (as this no longer routes via
the engine master (ign) switch
7 This feed is then delivered via a fuse to VHF and intercom.
8 Finally it was found that the co-pilots headphones/mike (IF not being worn were kept snug in the glove box) was adding unwanted back ground HISS and auditory input, simply disconnected- now silent!
Final worked around situation is ---
Separate battery feed to eliminate induction concerns over spiky 12 V supply. The spikes are from the facet pump, and were STILL there after replacing the facet pump with a "known quiet operating pump". Old pump reconnected.
The origin of the spiky 12V remains elusive.
Tx and Rx is now super -after many hours with the help of other (much larger) brains over quite a number of hours.
We can STILL hear engine is running on TxRx but this is simply via auditory input via the pilots mike!
It IS after all SUPPOSED to transmit sound, whether its speech OR back ground noise.
IMHO---->
Effective and reliable VHF transmissions remain one of our most needed, (essential) aspects of Safe operations,
second ONLY to general craft reliabilities.