JUMA PA1000 with KAT-500

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JUMA PA1000 with KAT-500

Postby LY2H » 19 Dec 2017 22:20

Hello Group !

I have jus have become a lucky owner of the Elecraft KAT500 Autotuner. I want to get lt running at my K3/ plus JUMA PA1000 ( which I become a lucky owner of a bit earlier) combo. K3 and JUMAPA1000 are working very nicely together after implementing of some very useful tips by Matti and others) So, now II would to listen to the impressions from the group on how have you set up KAT500 Antenna tuner work with PA1000? for example where did you take the PTT key line for the KAT500 to make it switchining between RX/TX?

Sesaon's Greetings! Merry Xmas!
73 de Linas LY2H
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Re: JUMA PA1000 with KAT-500

Postby K5TXT » 30 Jan 2018 03:15

Hi Linas,

Congrats on your new gear. This combination of KAT500 with the PA1000 looks interesting.

The enclosures are quite similarly sized (WHD).
KAT500 274 x 38 x 254/300 mm 10.8 x 1.5 x 10.0/11.8 in
PA1000 261 x 135 x 300 mm 10.3 x 5.3 x 11.8 in

Are you stacking the units? (Any chance for a photo?)
Some KAT500 users have placed it under their KPA500 due to heat concerns when using digital modes. But with the PA1000 not designed for 100% duty cycle key-down operation it's not clear if heat would be much of a concern with the KAT500 on top. Just follow the temperature indication I guess.

So a key question is how to best safely utilize this antenna tuner with the PA1000 driven by a QRP exciter?
The KAT500 includes amplifier-keying pass-through connectors (RCA jacks). This permits the KAT500 to interrupt the amplifier key-line during a tune or sudden high SWR condition. The KAT500 utility lets you set a power level whereby the amp key line will NOT open if RF is present to protect your transceiver, amplifier, and KAT500 from damage due to hot-switching.

Although Key Line / PTT connections are shown in the KAT500 Owner's Manual, that should not be relied on to prevent critically overdriving the PA1000 during an autotune sequence.

It seems one should alternatively just leave the tuner always set to manual - to help avoid inadvertent autotune mistakes when the amp is powered - and leave the exciter set to 10W. Since the firmware V1.17, it looks like the PA1000 will go to STBY when band is changing. Just remember to switch the amp to STBY before every manual antenna tune(!)

Can the KAT500 tune with just 10W?
I don't have a KAT500 to check, but the manual indicates: For better matching accuracy, tune with > 20W and: If a tune cycle is performed, 20 watts or more will produce more accurate tuning. But it's been noted elsewhere that although the KAT500 would like 20 watts to get a good tune it should be able to tune down to 10W.

It might be different though with QRP rigs at their 10W max output:
from K6KR - KX3 and KAT500 The KAT500 is not a QRP antenna tuner. The SWR bridge's voltage divider is designed for the 500 to 1500 watt range.  At QRP levels the SWR bridge voltages (and voltage differences) become quite small.   As reflected power drops near zero, it becomes difficult to measure small SWR differences. It's very difficult to find a minimum SWR when the ADC jitter exceeds the change due to a different tuner setting . . . . But the KAT500 should be able to select from pre-tuned solutions (what I have called a "memory recall tune") at any transmit level that is high enough for the frequency counter to work.  5 watts should be plenty. A "full search" tune is problematic at low power levels, particularly as exciters fold back (reduce output power) when asked to deliver their maximum specified output power into a varying SWR load during tuning.

Let us know of your insights on this ... (Just don't overdrive the amp).

You have a nice setup - hope to learn more about your experience...

Ryan - K5TXT
Last edited by K5TXT on 31 Jan 2019 09:49, edited 3 times in total.
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Re: JUMA PA1000 with KAT-500

Postby OH7SV » 30 Jan 2018 16:52

Hello all,

Do not route JUMA PA1000 PTT signal via any tuner because it can cause hot switching in PA1000.
The routing will spoil the PTT/RF timing coming from your transceiver. Typically the PTT signal (TX ON, SEND etc) comes abt 10ms before a transceiver is putting RF out and vice versa when you release PTT. Linear amp control timing can be set even longer in some transceivers. See your transceiver user manual.

I strongly recommend to wire the PTT cable directly from your transceiver to JUMA PA1000 according to user manual www.jumaradio.com/juma-pa1000

73 Matti OH7SV
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