[Elecraft] K3 and Sequencer

[Evert Bakker (PA2KW)]

Hi Tom (and others),

I think Don answered almost complete to your question but
I'd like to elaborate a little on this subject which is unnecessary for and
even unknown by most HF operators.

For serious VHF/UHF operation, it is important to have a system with low
noise figure (typical between NF=0.1 to 0.5 dB). For HF typical NF can be
between 3 to 10 dB. The ONLY way to reach this factor is by putting a preamp
as close as possible to the antenna. Each dB of cable loss, will raise the
NF with the same level and makes especially moonbounce more difficult or
impossible. A preamp in the top of the tower means at least 1 coaxial
(power) relay at the same position. These ralays have to be coaxial, and are
not that fast due to the mechanical construction (bigger distance between
contacts to enable big cross attenuation). Switching times are typical
longer then 20 msec.
To make absolutely sure that the relay has switched over, I (and many more
VHF operators) gets a feedback from the relay itself. Don't forget that all
is outside and vulnerable (cables, connectors etc).

Another issue in sequencing is that many VHF amplifiers are not build with
zero-bias tubes. So the grid voltage has to be raised and stable before
injecting RF at the input.

To overcome this problem and additionally prevent hot switching, a sequencer
is needed and 20 msec is not enough. A complete RX>TX sequence may even need
500 msec.

Here my motivation for an addition/change/option in the K3:

It would be far too much to ask Elecraft to develop and/or integrate a
sequencer. But as the Mic-PTT, external PTT, VOX, Key and/or paddle is
already combined into 1 single TX request (to the central processor) in the
HF-rig which finally puts the TX voltage on the parts needed (8T line) it
would be much more efficient for a small group of Elecraft users if that
signal is made available at one of the acc connectors. A TX-enable signal
from the sequencer to the HF-rig could close the loop or complete the
sequence so to say.

In my opinion it is almost all about software and could be activated only in
the tranverter mode of the K3. A regular HF user won't even notice this
option and therefore there is no need for a special VHF version of the K3.
So why not if it makes the radio interesting for this group. 
And don't worry, we will design, build or buy our own sequencers.
There are several thousands of serious VHF/UHF-ers. We are a market
opportunity, not a thread :-). We are not buying Elecraft equipment because
its appearance, but because it works so great and meets our expectations!

73's, Evert PA2KW

For 144 Mc
Ant: 2x16 el
Preamp: NF 0.3 dB
PA: YL1056 2.9 kW
XVRT: Home designed and build
TRCV: K2(4836)
 
For HF:
Ant: Optibeam OB11-5 / Alpha-Delta DX-B
PA: Drake L7
TRCV: Drake TR7/R7