[Elecraft] Update on BCI

[Sverre Holm - LA3ZA]

Here are replies to questions I have received on the cause of FM BCI
pick-up in the K2:

1. Filtering on power supply leads.
This has already been tried, and it is quite certain that the K2 picks
up the BCI directly on the RF board, either on some or more components
or the PCB-tracks itself. I suspect that maybe the relays (K16, K17)
that switch the preamp/attenuator in/out could pick up something since
they are possibly not shielded, but I am not certain, but moving a small
transmitter probe around does not produce any single position on the PCB
with maximum interference. I believe the problem can be identified and
fixed and thus make the K2 an even better tranceiver!
 
2. Switching the external RX antenna in/out. External RX antenna input
(160 m option) does not go through LP filters, so there could be more
sensitivity to BCI on that input.
Switching the antenna has no effect. The only control with effect on the
BCI is the Preamp/Atten control.

3. How can you receive an FM signal on a CW/SSB radio?
Every FM receiver has a detector which in effect is a frequency to
voltage converter. The slopes of the crystal filter give such an effect,
but much more narrowband than required for broadcast FM. Therefore one
will not get Hi-Fi sound, but will be able to hear rhytm etc from music
and be able to identify the station by comparing with an FM radio

BTW, if you want to hear this effect but don't have a nearby FM
transmitter, a 6 meter transmitter will do the job: 51.9 MHz will be
picked up at 14023 kHz, since the 3. harmonic of the oscillator is
(14023.33 + 4915)*3 which is 51900 + 4915




73, Sverre



Sverre Holm, LA3ZA
Asker, Norway (59.8N, 10.4E)
---------------------------------
www.qsl.net/la3za