Posted by
Randy Farmer on
Nov 30, 2018; 12:42am
URL: http://elecraft.85.s1.nabble.com/KPA-1500-issues-tp7646571p7646652.html
I've had difficulties with my KAT500 / KPA500 combo (only) on 160
meters, apparently due to the tuner relying on RF sensing. I've
carefully "trained" my KAT500 all across the 160 meter band. Since the
manual states that the tuning bins are 10 kHz wide below 3 MHz, I do a
tune at 1805, 1815 ... up to about 1895. My antenna is an impossible
load above 1900 kHz, so I don't try to tune up there. Since I don't have
exactly a great antenna system, I almost always stick to S&P operation
in 160 meter contests. As I tune across the band I can hear the relays
selecting the appropriate tuning solutions. But... every once in awhile,
as soon as I key the transmitter I hear the relays in the KAT500 switch,
presumably out of the commanded tuning bin due to frequency measurement
error in the RF detection circuit. This shouldn't be a problem, since
the tuning doesn't change significantly between adjacent bins. However,
since the amp is being keyed while the tuner is changing presets, the
amp immediately faults and goes off line. This is very annoying, and
probably not so good for either the amp or the tuner. If the RF
measurement resolution is really as poor as 8kHz, I don't see why
there's any point in providing for 10 kHz wide tuning bins on the low
bands. I would also strongly agree that if good frequency information is
available to the tuner via the serial bus that's what it should use to
select tuning bins. The RF sensing information should be a backup
source, to be relied on only in the absence of such data.
73...
Randy, W8FN
On 11/29/2018 4:57 PM, Don Wilhelm wrote:
> Andy and all,
>
> The KAT500 and KAT1500 tuner band segments are divided into frequency
> band segments - 25kHz wide on the lower bands and 50kHz wide on the
> upper bands if I recall correctly, so an 8kHz shift will not be
> significant unless the frequency shift moves the tuning into the
> adjacent segment.
>
> There is also a limit to how far the firmware will go to reducing SWR.
> In the interest of minimizing tuning time (and relay wear and tear).
> If the match is less than 1.3:1 or so, tuning will be declared
> adequate and will be stopped.
>
> Since the typical driving transceiver can tolerate an SWR of at least
> 2:1 without power foldback or damage, setting that 1.3:1 limit is
> reasonable - unless you are a 'purest' and mentally can only tolerate
> a 1:1 SWR (big grin).
>
> 73,
> Don W3FPR
>
> On 11/29/2018 5:42 PM, ANDY DURBIN wrote:
>>
>> "In addition the tuner may not always be in the segment you think it
>> is. This is due to the 8KHz resolution of the internal counter, that
>> wins over you sending it a more accurate frequency, and also the
>> hysteresis algorithm that can require a 2 segment frequency change
>> before the tuner changes. Gary from Elecraft says "if you are off by
>> one bin segment then it should not matter too much"
>>
>>
>> I have the same frustration with my KAT500 tuner. I send it a
>> frequency with 1 kHz resolution ( I was using 1 Hz resolution but
>> found that was futile) but it wants to override that frequency with a
>> much less accurate RF derived frequency. I suggested to Elecraft
>> that the frequency received over the serial interface should have
>> priority unless the RF detected frequency differed by more that a
>> user set threshold. That proposal was rejected on the basis that
>> here cannot be two master frequency sources. That argument was lost
>> on me since I have worked in the development of avionics systems
>> where master swaps are common and dynamic data source selection is
>> also common.
>>
>> I settled for sending my KAT500 a new frequency any time the actual
>> transmitted frequency differs from the KAT500 reported frequency by
>> more than 8 kHz. I have also tweaked FCCS and FCMD (not easy
>> because they don't seem to work as documented) to make is less likely
>> that RF detected frequency will usurp my serial data frequency at
>> least for CW transmissions.
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