[Elecraft] Tuner Loss question

[Fred Jensen]

On 2/11/2014 9:47 AM, Jobst Vandrey wrote:
> I have lots of data in the loss to be expected in Coax or Open wire when
> running at higher SWR into a multiband antenna  - however, I do NOT have
> any real world data on the losses to be expected in a tuner system at
> higher SWR.

Obtain some sheet syrofoam and an indoor-outdoor remote reading 
thermometer.  Build a box from the styrofoam, enclose the tuner inside 
it with the remote temp sensor and seal the box up.  Record the 
temperature.  Fire up your TX into the tuner feeding the load of choice 
and let the temperature stabilize.  Be sure and ID every 10 mins.

Meanwhile, calculate the mass of the gas inside the box from its 
dimensions, the barometric pressure when you sealed up the box, and the 
Ideal Gas Law [PV=nRT].  Once the temperature stabilizes, you can 
calculate how much of your TX energy went into heat inside the box.  The 
rest went up the coax.  Calculate the loss from L[dB]=10*log[Ph/Po] 
where Ph = power lost to heat and Po = TX power.
>
> So:
>
> Are there any numbers available on what additional losses my Elecraft K3
> (SN 5283) antenna tuner will experience when the SWR is high - say about
> 5:1 or higher when feeding a multiband antenna with 50 Ohm coax on 20
> meters?  Should I expect another 3 dB down in signal strength during
> receive - and also Transmit?  Or are the losses higher or lower then that?
>   Also, are the losses frequency dependent (like on coax) or are they the
> same across the bands.

Seriously, the best way is to find a technical review of the tuner by 
someone with all the appropriate test equipment.  Intrinsically, every 
tuner has loss that depends on many factors such as the Q of the 
inductors, the L/C ratios required to match a given load, the complex 
impedance presented to the tuner by the load, and the current phase of 
the moon.  However, it is very difficult to measure power in 
non-resistive situations and the odds that the loads presented by your 
multiband antenna are all resistive is right behind the odds you are 
pregnant with twins.  OK, I made up the part about the moon.  I seem to 
remember a QST series on tuner losses a few years ago, don't know if the 
KAT3 was one of the ones tested.

In reality, it is what it is and if you found the losses to be high at 
some combination, there's not much you can do about it save re-design 
your antenna system [or get a different tuner].

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

PS:  I strongly urge the List Lurkers to get a little chuckle out of the 
imperfect physics in the first graf and resist the urge to correct my 
rendition.  While I did, in 1959, manage to measure with pretty good 
accuracy the efficiency of a 10KW FM Class C PA using real physics very 
similar to my rendition above, I left out a lot in the tuner example.