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

Wed Aug 24 20:18:58 EDT 2022

On 2022-08-24 16:19, Fred Jensen wrote:
> 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,

*** What kind of motor does it have?  I've been planning to use a
stepper, controlled by a microcontroller.  Use frequency data from
the radio ( or at least band data ) to get it into the ballpark, and
then zero in onto resonance.

   It's not going to be a portable system.  The size of the capacitor 
alone
guarantees that.  I'm going to either mount it on a mast, or on top of a 
shed.

                - Jerry, KF6VB

  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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