[Elecraft] KAT500 Attenuator

[Bob McGraw]

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-request at mailman.qth.net wrote:
> Message: 4
> Date: Fri, 10 Dec 2021 13:30:16 +0000
> From: Andy Durbin<a.durbin at msn.com>
> To:"elecraft at mailman.qth.net"  <elecraft at mailman.qth.net>
> Subject: [Elecraft] KAT500 Attenuator
> Message-ID:
> 	<SJ0PR16MB4032D9FD2C7C6E0B9CE90B358C719 at SJ0PR16MB4032.namprd16.prod.outlook.com>
> 	
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>
> 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