[Elecraft] KX3 and its "TUNE" selection. (With mag loop)

Fred Jensen k6dgwnv at gmail.com
Wed Aug 24 19:19:40 EDT 2022 

Tuning on most mag loops is very touchy, and more so on lower 
frequencies, because of the extremely high Q.  My Alexloop has a 
reduction gearbox on the capacitor, and I wish it had 3 times the 
reduction it has.  I doubt you could get close enough with a 
motor-driven cap to a preset position. And, exact resonance matters. 
However, it's pretty easy these days to use a V-I sensor and a phase 
detector to determine where resonance exactly is, and have a little 
microcontroller drive the cap to zero phase difference. We used to do it 
with HF mobiles.  Still may be done.

Most of the cost in transmitting loops >QRP is in the vacuum variable 
capacitor, the construction to minimize I-squared R losses, and to 
withstand the extremely high voltages which, at 100+ watts can range 
well above 100 amps circulating current and multi-KV potentials.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

Geoffrey Feldman wrote on 8/24/2022 12:11 PM:
> Magloops with effective remote tuning are very pricey but those are not (as far as I know) automatic tuning, just remote)  With a tiny bit of practice, it’s not hard to do manually.  I give it almost no thought.   To simply have a mag loop go to the perfect spot of resonance in response to instructions from the radio would be difficult if not impractical.
>
>   
>
> The key thing here is that it’s not a problem (for low power) to have the mag loop close to you nor is it hard to adjust it (as I described) to be perfectly resonant to the radio.
>
>   
>
> However, Julia is right.  You can have the KX3 report its frequency (and everything else) through the ACC1 port.  Similarly the KX3 can be controlled by this magic box (to transmit a bit)   Getting a mag loop with its very high Q to perfectly tune to that frequency would be interesting.  When you see how tiny the changes to the Variable Cap are – you might perceive the problem.   Are there effective auto-tuning magloops that work as perfectly as hand tuning for low power levels?  I’d like to know.
>
>   
>
> I also think that complexity can get in the way of portability. The beauty of the mag loop I have (alex loop) is that it’s light weight, quick to set up and take down.  Adding complexity would change all that.  At that point, I would use the kxpa100 with its tuner. (possibly even cheaper)
>
>   
>
> W1GCF
>
> Geoff
>
>   
>
> From: Julia Tuttle [mailto:julia at juliatuttle.net]
> Sent: Wednesday, August 24, 2022 12:53 PM
> To: jerry
> Cc: Geoffrey Feldman; Elecraft; JEROME SODUS
> Subject: Re: [Elecraft] KX3 and its "TUNE" selection. (With mag loop)
>
>   
>
> Hi Jerry,
>
>   
>
> That's absolutely possible over the serial port (ACC1)! The Programmer's Reference has the details:
>
>   
>
> https://ftp.elecraft.com/K3S/Manuals%20Downloads/K3S  <https://ftp.elecraft.com/K3S/Manuals%20Downloads/K3S&K3&KX3&KX2%20Pgmrs%20Ref,%20G5.pdf>  &K3&KX3&KX2%20Pgmrs%20Ref,%20G5.pdf
>
>   
>
> 73,
>
>   
>
> Julie
>
>   
>
> On Wed, Aug 24, 2022, 12:49 jerry<jerry at tr2.com>  wrote:
>
> I'm starting work on a magloop project.  I wonder how hard it would be
> to
> have a transceiver tell the magloop what frequency it's tuned to?  That
> could
> operationally be simpler than having to hit it with low-power RF so it
> can tune
> itself...
>
>                      - Jerry, KF6VB
>
>
>
> On 2022-08-23 14:28, Geoffrey Feldman wrote:
>> If your antenna is a magloop - DO NOT USE the tune button. In fact,
>> clear
>> the tuner memory for your band per instructions.   The tuner feature
>> (assuming you have the option) is great with other antennas, especially
>> random wire but it doesn't go well with mag loops.  The xmit button is
>> simply "PTT".
>>
>>
>>
>> For any mag loop, choose a frequency you wish to start work, somewhere
>> in
>> the middle of the band.  Mag Loops are high Q antennas, that is they
>> are
>> effective in a very narrow range of frequencies to which they are
>> adjusted
>> with the tuning box.  This fact should inform your thoughts on
>> effective
>> use.
>>
>> Turn the tuning dial (ON THE MAG LOOP) until you hear the maximum
>> amount of
>> noise (or blessed with a real signal).   The antenna and the radio are
>> now
>> tuned.
>>
>> Turn the KX3 tuning knob SLOWLY until you hear some kind of interesting
>> signal.  (PX3 is great for this too).
>>
>> Tweak the tuning knob on the mag loop to get the strongest signal for
>> your
>> exact frequency. (just a tweak).   This is important even if you hear
>> the
>> signal, to get the most efficient use of transmitter.
>>
>> If while seeking a station you hear a lot less static, adjust the mag
>> loop
>> as above.
>>
>>
>>
>> IF seeking up and down the band, just rinse and repeat as above until
>> you
>> get a station to work.
>>
>>
>>
>> Once the mag loop is tuned to the band, you won't have to adjust it
>> much to
>> tune it for the particular part of the band you are on. Gentle tweaks
>> is the
>> way.  Notice too, mag loops are very directional. Consult the
>> manufacturing
>> manual for where it's sensitive and turn it along a great circle to
>> where
>> you want to go.  (In Boston, where I live, Europe is north east by
>> great
>> circle.
>>
>>
>>
>> I note there is something about tuning the radio in some mag loop
>> instructions.  I find this not necessary with the KX3.  What I describe
>> here
>> is what I do and it works well.
>>
>>
>>
>> I have contacted Europe USB with a KX3 at 15 watts and a mag loop.  The
>> antenna was on the top floor of my wood frame town house for this, not
>> even
>> outdoors.  If you think about what I wrote, you want the antenna in
>> arm's
>> length while working the radio.  Don't worry about your body affecting
>> the
>> near field. Mag Loops are not like that.
>>
>>
>>
>> -73-
>>
>> W1GCF
>>
>> Geoff
>>
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