I took the cover off mine and verified that the shunt resistor was missing and
the series one measured 228 ohm. Clearly, if this is dynamically switched while
seeking a match the poor exciter is going to be totally confused. The
attenuator should have been implemented with two 30 ohm resistors in the first
place. What motivated them to remove one is a mystery.
The fact that mine appears to have changed value says to me, that while clever,
the use of the bottom panel for a heat sink is problematic. I suspect this is
also the case in the K3/K3S LPA where there are a lot of FET failures.
Wes N7WS
On 12/12/2021 8:48 PM, Bob McGraw wrote:
Just went through different antenna configurations and bands. Using the KAT500
Utility, selecting the ATTENUATOR and then TUNE on my K3S shows a SWR of 1.5:1
and when the ATTENUATOR is not selected the SWR shows 1.1:1. An external
SWR/PWR meter in the line between the radio and KAT500 shows the same values.
In receive mode, I hear a relay click when selecting the ATTENUATOR and again
when de-selecting the ATTENUATOR. Also noted the RX signal drop about ~3 dB
{maybe less} when the ATTENUATOR is selected.
I did notice initially when selecting the ATTENUATOR it seemed to be
inconsistent in results for a few times. I figure this is some issue with
relay contacts. Once exercised 3 or 4 times, no further strange operation
was observed.
Don't have a clue if the resistors in question are installed or not.
I recall that certain ICOM tuners insert an attenuator on the input when
running the tune routine. This is said to provide a constant impedance/load
to the transmitter while the tuner runs through its range of L and C values.
This of course is for a radio that folds back power when the SWR is >3:1 or so.
73
Bob, K4TAX
On 12/12/2021 7:24 PM, elecraft-requ...@mailman.qth.net wrote:
Message: 4
Date: Fri, 10 Dec 2021 13:30:16 +0000
From: Andy Durbin<a.dur...@msn.com>
To:"elecraft@mailman.qth.net" <elecraft@mailman.qth.net>
Subject: [Elecraft] KAT500 Attenuator
Message-ID:
<sj0pr16mb4032d9fd2c7c6e0b9ce90b358c...@sj0pr16mb4032.namprd16.prod.outlook.com>
Content-Type: text/plain; charset="iso-8859-1"
KAT500 has an input attenuator that may, under certain conditions, be
activated during a full search tune. Page 1 rev C of the KAT500 schematic
shows the attenuator is a divider consisting of R6 and R7 which are both 39
ohm. My KAT500 serial number 2609 does not have R7 fitted and R7 is shown as
not populated in Figure 17 of KAT500 User's Manual Rev C6.
The removal of R7 changes the potential divider into a simple series resistor
and my measurements show my KAT500 presents a very poor match to my TS-590
exciter when the attenuator is active. In this example the KAT500 was in
bypass and connected to a nominal 50 ohm dummy load. The impedance presented
to my TS-590 by KAT500 was measured with an LP-100A:
Att Out: R 48.1, X 2.4, Pwr 4.48, SWR 1.06
Att In: R 22.3, X 162.6, Pwr 0.55, SWR 9.98
Do other KAT500 owners see similar results? (Attenuator can be switched
in/out with KAT500 utility)
Can someone please explain why the attenuator was changed.
Thanks and 73,
Andy k3wyc
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