[Elecraft] K3 - Receiver desense?

[Jeff Cochrane - VK4BOF]

Hi everyone,
I have an interesting phenomenon happen yesterday whilst operating on 15M mobile/portable with my K3.
Here's some background info first.
The vehicle is a Nissan D21 series Navara of 1991 vintage.
It has a brand new alternator, battery & kettering type ignition systems and whilst old and high milage (570,000Klm), still runs like clockwork.
(The vehicle does not have a computer onboard as it does not have EFI, ABS or electronic ignition)
The K3 is serial #4257 and is up to date with all firmware,. mods etc. (Firmware 4.31 in fact)
The issue:
Whilst parked up in the car and with the K3 running on 15M during CQ WW SSB I noticed that the display lights were flickering alot on TX, indicating to me that maybe it was time to start the engine to increase voltage to the rig.
Received sigz at the time were plentiful (crowded) and loud, the band was wide open.
So, I started the engine and all sigz but for a couple of what used to be loud signals had disappeared!
The really loud sigz I had heard before were considerably reduced in volume and signal strength.
I checked the NB and NR settings and found that both noise blankers were both turned off as was noise reduction off.
I tried both NB's and neither were of any use.
There was no type of noise heard on the radio at all apart from the usual (low down) band noise.
All the above was noted when I was using the cars own battery / power system.

I shut down the engine and all sigz came back to normal.

As I had an extra truck battery in the tray of my vehicle (I had been out of a field day with Gary VK4FD and others) I decided to try that in the same scenario.
So, I shut down the engine and the radio and transfered the radio power leads to the external truck battery.
No problems were noted at all.
All sigz on 15M were loud and no issues were noted even if the engine was running.


Now, can anyone explain it?
Very little ignition noise was noted in the receiver and it could be removed by setting the DSP NB to 5-1, the IF NB was not effective at all in removing the noise so it was left turned off, which is where I have always had it set to.


Over to you all,

Jeff Cochrane - VK4BOF
Innisfail, QLD, Australia