[Elecraft] K1-4 on 30/20/17/15 ?

[Mike Morrow]

David wrote:

>I would like to setup a K1-4 for 30/20/17/15, which I believe would need an LPF
>for 20 and 15).  I believe I can do this with all of the parts that come with a
>K1-4 except that I don't know if it includes an LPF for 20.

As supplied, the K1 with KFL1-4 covers 40m, 30m, and any two of the 20m, 17m, or 15m bands.  It does NOT cover ANY four of the 40m, 30m, 20m, 17m, 15m bands.   Actually, K1 product literature claims that the KFL1-4 coverage is 40m, 30m, 20m, and either 17m or 15m, but the KFL1-4 is actually a little more versatile than that.  I guess they thought no one would ever give up 20m coverage.

It has two LP filter sections in the transmitter output/receiver input signal path.

One LP filter section is switched in by firmware for the two lowest bands (40m and 30m), with a filter cutoff somewhere above 30m but below 20m, where the second harmonics of 40m operation would appear.  

The other transmitter LP filter section is switched in by firmware for the two highest bands (any two of 20m, 17m, 15m), with a cutoff somewhere above 15m but below 10m, where the second harmonics of 20m operation would occur.

Thus, as supplied, the KFL1-4 won't cover 30m, 20m, 17m, and 15m because you'd be trying to put 30m and 20m signals through the same LP filter that cuts off below 20m.

Additionally, it would be hard to juggle around the values of the fixed capacitors in the pre-mix and the RF band-pass filters to accomodate 30m and 20m operation for the firmware-programmed bandswitching relay latching action that takes place for 30m and 40m operation.

Of course, KFL1-4 firmware could be modified to select one LP filter section for only one band (30m), while selecting the other LP filter section for the other three bands (20m, 17m, 15m), but we don't have the option of altering the KFL1-4 firmware.

Your combo is not impossible, but it would take some study, BP/LP filter redesign, and additional parts (fixed capacitors).  But be careful.  The K1 has the best spurious output specs of any Elecraft rig, and re-design could sacrifice that spec. 

IMHO, it would be best to choose a combo of bands that the KFL1-4 already supports.  Trading off 17m for 40m isn't much of a penalty.  It gives you a good night-time band any time of the year or solar cycle.

73,
Mike / KK5F
K1 No. 175 (Nov. 2000)