Re: QSX radio feature requests

J68HZ
 

Hey Arv… Oh the binary approach does work.  Eventually.   My comment was more along the lines that it’s the most inefficient way to get to a match.  I did a lot of research around algorithms used to solve the classical binary tuning problem years ago (8 discrete coil, 8 discrete capacitors… 65535 combinations.).  The best hunting algorithm uses a newton gradient approach to finding the solution (calculate the derivative basis your swr readings).  It’s also the fastest of the hunting algorithms.  Smarter approach… one used by most military tuners… it to calculate the real and imaginary parts of the load at the frequency of interest.  Then calculate the transform to give you exactly 50 ohms real… and implement that as a solution.  It’s like plotting the load on a smith chart and drawing the two-step solution to get to 50 ohms.  It’s obvious from the diagram what to do.  Since there can be a bit of error in the calculations, these algorithms usually either stop and live with a tiny bit of SWR or they then switch to a halving algorithm to tough up the SWR by looking at reactive components on either side of the calculated solution.  This is also covered in Sabin’s book.   This approach is way faster than the binary/ hunting approach unless you start at the solution to begin with… at which time they both have about the same solution time!

 

Latching relays.  I started looking for some good quality, small,  latching RF relays capable of 100 watts.  I found two types… a single coil-reverse voltage to change state (must be magnetic), and dual coil models (flip flop).  I eventually settled on the dual coil model as they are easier to implement than reversing the coil polarity.  I found what I needed on Alibaba… It was a direct from the factory deal for several hundred.  I asked for a sample to try first.  When I was satisfied they worked, I bought several hundred.

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

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email:  bill@...

 

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of Arv Evans
Sent: Saturday, August 25, 2018 10:22 AM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QSX radio feature requests

 

Bill

My own QRP ATU uses binary progression of inductances with a 0-150 pf

variable cap and a switch for adding another 150 pf fixed C.  It doesn't seem

to be too much of a stretch to have the C values also binary progression. 

Might take a bit of thought for those not used to programming in machine

code but it does seem doable. 

I'm curious about how small latching relays work.  My only experience in

that area is with much larger units.  They had two coils, one to operate the relay

and another to release the lock.  Do the small ones work that way. or is

there some other methodology?  Magnetic latch?

Arv
_._

 

On Fri, Aug 24, 2018 at 8:17 PM J68HZ <bill@...> wrote:

Woah, wait.  Toggle switches to replace the relays???!!!!  So how do you propose that would work… do a binary search towards a low SWR solution?  That reminds me of loading the operating system into an ATARI 8080 system using front panel switches…  could take forever and a few days.  If you are worried about current draw, go with latching relays.  Back in March, I bought several hundred latching relays for $0.89 each… yes they can be had cheap if you buy them right from the source.

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook!

 

Moderator – North American QRO Group at Groups.IO.

 

email:  bill@...

 

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of Arv Evans
Sent: Friday, August 24, 2018 8:18 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QSX radio feature requests

 

Glen

The K3NG ATU is an interesting design but uses several relays.  That is fine for automation

purposes, but I wonder if the design could be reproduced with a handful of DPDT rocker or

toggle switches replacing the relays.  Maybe there needs to be 2 versions of this well thought

out design, one that is automated and another that is manual for low current draw and increased

battery life for portable use.

Arv
_._

 

On Fri, Aug 24, 2018 at 6:27 PM Glenn <glennp@...> wrote:

The K3NG ATU lends itself to home brew.   And changes to the power level required. My own build I estimate at around 20-30W and uses smd 2-3kV caps (overkill) and the usual relay switching of L&C. Two relays are used to switch the ends for L-C or C-L. I used standard relays, not latching, due to cost here in VK. Control board uses a NANO with a 0.96" OLED display.

vk3pe

 

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