[Elecraft] KAT500 Attenuator

[Wes]

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-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> 
>>
>>
>> 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
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to wes_n7ws at triconet.org