[OT] Bluetooth and RF

[Thomas Horsten]

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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[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
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Fred Townsend]

Tom with good engineering practice there is no reason why you can't
successfully connect using BlueTooth. However good engineering practice
isn't always practiced. That's why any commercial manufacturer, constructing
an appliance of the kind you describe, must undergo certified testing.
However I don't see that as a major obstacle, even if you are not an
engineer.
What did raise my concern is your AVR. Your AVR will most likely have a
24MHz (hello 12 meter birdies) or 48MHz clock although it could be as low as
12 MHz. It is particularly important your AVR be properly housed and
shielded with attention to bypassing of power supply leads even if you are
using battery power. Your data cables will likely need some ferrite lumps
too.
A continuous tuning receiver is a great tool for checking your design. The
beauty of amateur radio is you can experiment  with your design without big
brother looking over your shoulder.  After all you will be the first person
to suffer if you have RFI problems.
Go for it Tom.
73, Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Thomas Horsten
Sent: Thursday, July 05, 2012 4:06 AM
To: [hidden email]
Subject: [Elecraft] [OT] Bluetooth and RF

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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html