[Elecraft] [OT] Bluetooth and RF

[Matt Zilmer]

Hi Thomas,

Consider that BT is often used in smart phones, usually as a headset
or hands-free link.  If the phone is GSM, power levels of 2-3 W are
common when getting connected to a new BTS (base station), upon
handover or at  power on, to get connected to the cell network.

BT and its antenna are in very close proximity to the antenna of the
phone itself, so such a design *can* be done and often is.  Worldwide
cellular frequencies include 800-900 MHz, 1.8, 1.9, and 2.1 GHz
(others?).  The upper ones are close-in to 2.4 GHz, BT's range.
Somehow, designers keep the two from interfering with each other.

Most phones use a diplexer (I think...) to do the obvious, but I'd
also think that frequency separation of BT from some of the bands
makes this redundant.  And most phones actually use separate antennas
for their several functions (GPS in L-band, GSM in whatever band, BT
and WiFi in the 2.4 GHz band).

More problems might occur from RFI getting into the digital control
side than from anything analog.  Still, the KX3 is well shielded and
using a good coax with no radiation from the braid would be advised
(use a balun or a resonant antenna).  I agree that your HF antenna's
proximity to the accessory might be the biggest problem with RFI.

matt W6NIA
KX3 #6 / FT

On Thu, 05 Jul 2012 12:05:43 +0100, you wrote:

>Hi guys,
>
>I know it's a bit off-topic but there are so many knowledgeable people here
>that I thought I'll try asking. I've built a multifunction CW keyer with a
>straight key, paddle, and keyboard input, that uses an AVR microcontroller.
>Currently I'm using PS/2 for the keyboard input as it's easy to implement
>in the AVR (and a cheap $2 adapter allows the use of USB keyboards).
>
>But for taking on the road with my KX3 (which is stuck in customs since
>Monday but should hopefully be with me soon), I'd like to use an
>ultra-compact Bluetooth keyboard, of the type used with smartphones. I am
>considering doing this by adding a Bluegiga WT12 Bluetooth module (which
>has an UART interface that can talk to the AVR).
>
>Before I begin on this I'd like to know how well Bluetooth can be expected
>to work in a RF-filled environment (at up to 10W but with the antenna very
>close, as in portable operations). It'd be a shame to get everything built
>only to find out that the Bluetooth connection dies every time I transmit.
>Has anyone got experience with this and/or other comments/ideas?
>
>73, Thomas M0TRN
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