Re: QCX tuning


The LDG Z-100Plus requires only 0.1 watt to tune according to LDG and is rated for 125 watts which leads me to think that it has lower losses than some of the "QRP" tuners with much lower ratings.  Dunno for sure about that.  It uses latching relays so power consumption is almost zero once tuned. 
No relation to the company...just a satisfied user.
-Lee-    WA3FIY

------ Original Message ------
From: "Richard Harris via Groups.Io" <g3otk@...>
Sent: 9/1/2018 2:07:18 PM
Subject: Re: [QRPLabs] QCX tuning
Hi Matthias,

When tuning, the T1 auto-ATU may present an impedance to the QCX that causes excessive current to flow through the PA FETs or causes an excessive voltage across them  One solution is to connect an attenuator between your QCX and T1 auto-ATU when it is tuning and disconnect it when a match has been found.   This will limit the range of impedance "seen" by the PA FETs.  A 3dB attenuator will ensure the QCX "sees" a load between about 17 and 150 Ohms.  A 6dB attenuator will ensure that the load is always between about 40 and 85 Ohms.  

When I built an auto-ATU for my 20m QCX, I thought that damage to the PA FETs was possible and so while the ATU is tuning an attenuator is switched into circuit by means of a relay.  

Richard G3OTK

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