[Elecraft] KPA-1500 wish list

[K9MA]

When you QSY, without switching antennas, it seems to take half a second 
or so after you stop tuning for the ATU to switch. (Assuming it's been 
"trained".) As far as I can tell, after that delay the ATU is stable, so 
it shouldn't affect outgoing CW. However, as Pete says, when you switch 
antennas there can be a delay, since the only way the ATU knows you have 
switched antennas is the high SWR when you start transmitting. The 
solution is a way to tell the ATU that you have switched antennas BEFORE 
transmitting, for example, by tying it into the switch(es) which 
controls the external antenna relays.

Imagine this scenario: You hear a weak signal calling CQ, flip your 
antennas switch a couple time to figure out where it is coming from, and 
then you have about 100 ms to start calling. Otherwise it's too late. 
With two tribanders, this happens to me all the time. How can the 
KPA1500 ATU be made to switch that fast? It's relays certainly can; it's 
just a matter of getting that control signal to them.

I doubt there is any way to modify the KPA1500 to make this happen 
without changes to firmware.

73,
Scott K9MA

On 11/20/2019 08:40, N4ZR wrote:
> I hope that the amp guys at Elecraft will reply to this thread.  I've 
> been working with them for several weeks trying to address just this 
> problem.  The latest beta firmware seems to handle it pretty well, so 
> long as I make sure I've trained the ATU on every band segment.
>
> I'd love to have 50-ohm resonant antennas on every band.  Short of 
> that, there does not appear to be any way around the ATU's need to 
> identify which antenna is selected by the external switch, before it 
> can decide which stored setting to apply.  This takes a measurable 
> amount of time, as much as one character of 30 WPM CW, and I'm told 
> that until this process is completed, the amplifier is bypassed.  I've 
> observed, for example, that when I pounce on a CQer significantly far 
> away from the frequency of my last QSO, the "N" in my call becomes 
> "E", or goes away entirely, as heard by the other station.
>
> 73, Pete N4ZR
> Check out the Reverse Beacon Network
> at <http://reversebeacon.net>, now
> spotting RTTY activity worldwide.
> For spots, please use your favorite
> "retail" DX cluster.
>
> On 11/19/2019 3:56 PM, K9MA wrote:
>> Bill is touching on an issue I've raised before: A way to select 
>> multiple ATU settings for the same frequency and antenna output. I 
>> had to build a tri-band tuner to switch between my two tribanders so 
>> they would both present the amplifier with the same impedance. The 
>> internal ATU would have been able to do that, if only there were a 
>> way to store and recall two different sets of settings. In the case 
>> of automated antenna switching systems like mine, there also has to 
>> be a way to electronically tell the amplifier which settings to use: 
>> Having to press a front panel switch is not acceptable, as that would 
>> require two operations to switch antennas, which is way too slow. (I 
>> sometimes have to flip the antenna switch several times during a call 
>> to determine which antenna to use.)
>>
>> 73,
>> Scott K9MA
>>
>>
>>
>> On 11/19/2019 13:02, K8TE wrote:
>>> Another issue not explicitly mentioned is using an external antenna 
>>> switch
>>> with different conjugate matches already trained withing the KPA1500 
>>> ATU.
>>> Those different matches mean when one selects a "new" (different) 
>>> antenna
>>> than already selected on a particular frequency (same band or not), the
>>> KPA1500 doesn't know this fact until power is applied.  Then, due to 
>>> a high
>>> VSWR, the amplifier faults.
>>>
>>> With just two antenna ports on the KPA1500, there are only two quickly
>>> accessible tuning solutions per frequency if using both ports. If using
>>> only one port and an external antenna switch, a common choice in many
>>> stations, finding the correct tuning solutions can't be done fast 
>>> enough to
>>> prevent a fault.
>>>
>>> As alluded to in previous messages on this topic, perhaps the solution,
>>> unfortunately, is an external box that could contain the appropriate 
>>> data so
>>> that, when a new frequency/antenna combination, that has a 
>>> previously tuning
>>> solution, is selected, the external box will tell both the KPA1500 
>>> ATU to
>>> select the appropriate solution and transceiver to make appropriate 
>>> power
>>> level adjustments, both PRIOR to actually transmitting.
>>>
>>> This is done (approximately, but with no power level changes) by the 
>>> KAT500
>>> in selecting one of the three antenna ports and the appropriate tuning
>>> solution.  This assumes no other antenna choices on each of the 
>>> three ports
>>> for the same frequency.  The KPA1500/K3S combination is (currently) not
>>> sufficiently "smart" to accomplish this.
>>>
>>> Of course, if we had "perfect" antennas that provided resonant 
>>> matches on
>>> all bands/frequencies, we wouldn't be discussing this.  If we had 
>>> those, we
>>> wouldn't need the KPA1500 ATU either.  73, Bill, K8TE
>>>
>>>
>>>
>>> -- 

-- 
Scott  K9MA

k9ma at sdellington.us