[Elecraft] Elecraft T1 auto tuner question

[David Gilbert]

The T1 specs say that it should function with input power as low as 0.5 
watts.  An 8 dB attenuator at the output of your 4-5 watt QRP rig should 
still give you close to 0.5 watt into the T1, and the attenuator acts as 
a buffer that diminishes the reflected power from the high SWR load.  
Tune with the attenuator in place, and then remove it after the match 
with the T1 is achieved.

https://www.rfcafe.com/references/electrical/vswr-reduction.htm

https://www.rfcafe.com/references/calculators/vswr-return-loss-conversion-calculator.htm

According to the 2nd link, an 8 dB attenuator would turn a 20:1 SWR at 
the load into less than 1.4:1 at the output of the rig.

HUGE CAVEAT:  An attenuator designed for 8 dB only gives the design 
value reduction in reflected power for input and load impedances that 
match the design of the attenuator.  An attenuator designed for 8 dB 
with 50 ohm input and output won't give 8 dB with radically different 
impedances.  That being said, it doesn't take much attenuation to help 
and I think it would be worth a try.  I can't think of any other way to 
do what you want unless the T1 can be manually stepped through a match 
and you monitor the input with a VNA (NanoVNA, for example).

There are a lot of T-network attenuator calculators out there ... here 
is one of them. https://www.pasternack.com/t-calcualtor-tee-attn.aspx

73,
Dave   AB7E





On 5/22/2023 11:52 AM, n7tb at comcast.net wrote:
> I have a T1 that I have used for several years.   I recently purchased a
> QCX-mini, and an SW-3B.  I normally use my K2, KX2 or KX3 for portable
> operations, but occasionally I like to use something different for QRP CW.
> Both the QCX-mini and the SW-3B require a 2.0 or less SWR.  The
> documentation for SW-3B says that operating at any SWR over 2.0 will damage
> the radio.  The outputs varies with voltage, but usually runs at 4-5 watts
> with a 12V supply.  If I attach the T1 to that rig, and perhaps the QCX-mini
> as well, it will require the rig attached to present a constant carrier to
> tune.  This seems to eliminate using an auto tuner with the SW-3B at a
> minimum in that configuration.
>
>   
>
> Can someone tell me how I might get the T1 to tune in the field with
> something other than the rig.  If I could trigger it to tune, then I could
> attach to the radio after the tune cycle.   My plan is to use a resonant
> antenna, but that may not always be possible, especially with a three band
> rig like the SW-3B.
>
>   
>
> Thanks,
>
>   
>
> Terry, N7TB
>
>   
>
>   
>
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