[Elecraft] KX3 tuner loss?

[Barry N1EU]

It ends up that John KN5L gave a thorough treatment to the topic in this
thread (might need to be a member of the KX3 Yahoo Group to read):
https://groups.yahoo.com/neo/groups/KX3/conversations/topics/5869

73, Barry N1EU

On Thu, Nov 3, 2016 at 4:08 PM, Ron D'Eau Claire <ron at cobi.biz> wrote:

> You ask a commonly asked question. And, as usual, no responses so far.
>
> I can't give you an estimate either because first, the losses are highly
> dependent upon the impedance transformation. You'd need to characterize
> that
> doublet and feed line (the length of the feed line is important) to see
> what
> impedance it presents to the ATU.
>
> Then you need to measure the ohmic losses in the ATU inductors, wiring and
> connectors. Dielectric losses may occur but with modern gear they are very
> tiny at HF.
>
> Finally you calculate the currents flowing in the ATU at each impedance
> transformation required to achieve a match to your feed line so you can
> calculate the losses based on the resistance of the wires, inductors, and
> connectors.
>
> Personally, I accept the idea that an L-network (which all the Elecraft
> ATUs
> use) is highly efficient and leave it at that.
>
> If I were really inclined to actually measure the loss, I'd first measure
> the RF power output into a stable 50 ohm load without the ATU in the
> circuit. Measure with an external wattmeter at the load as well as the KX3
> output power indicated.
>
> Then I'd breadboard another L-network with a variable cap and variable
> inductor, connect it to the 50 ohm load and to the KX3 output, transmit and
> adjust the external L-net (not the KX3 ATU) for a 1:1 match. In that way
> you
> have created a known dummy load that presents the same complex impedance to
> the KX3 as your antenna system.
>
> Now you can transmit at the same power at the KX3 as before and see what
> the
> power is at the 50 ohm load. Actually, you will be seeing what the power is
> after passing through both matching networks.
>
> My guess is that you'd find the total loss so low you won't be able to read
> the difference on the two power meters.
>
> A more direct approach would be to isolate the ATU in a very well insulated
> enclosure, transmit, and measure the temperature rise until it stabilizes.
> You can then calculate how much energy is being dissipated by the ATU and
> becoming heat. That requires the ATU be carefully isolated from the rest of
> the KX3 and be in a very well insulated enclosure to avoid loss of heat to
> the environment, something not practical to do with a KX3. It is, however,
> a
> valid way to determine losses in external devices like an RF transformer
> (e.g. "balun").
>
> I suspect this explains why few (if any) Hams bother to make the
> measurements.
>
> 73, Ron AC7AC
>
>
>
>
>
> -----Original Message-----
> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
> Barry
> N1EU
> Sent: Thursday, November 3, 2016 7:20 AM
> To: elecraft; KX3 at yahoogroups.com
> Subject: [Elecraft] KX3 tuner loss?
>
> I'd appreciate knowledgeable estimates of the loss in dB through the KX3
> ATU
> when working into a 44ft (NorCal) doublet fed with twinlead, with or
> without
> a BL2 balun inline, on 20/17/15M.
>
> Thanks & 73,
> Barry N1EU
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