[TowerTalk] [Bulk] Re: SteppIR

[Grant Saviers]

However, stepper motors are notoriously tricky in real mechanical 
systems because of the system dynamics.  They impart high frequency 
energy (think square wave Fourier series) and have devilish internal 
magnetics which lead to resonances.  Since "servo" usually means a 
closed loop system, a "stepper servo" has to have a separate position 
reference for feedback position accuracy and usually for loop 
stability.  CNC tools with large stepper motors are made with various 
types of position sensors and thus are servo "closed loop" controlled.  
Inexpensive machines have no feedback loop and are open loop, risking 
where the tool is and where the controller thinks it is are different.  
This can lead to ugly/expensive tool crashes.

If a stepper is driven slowly, or the system dynamics are precisely 
known and constant then they work ok for positioning.  Slow is the case 
in a steppIR.  Note, however, that there is a "recalibrate" button on 
the steppIR controller for when what the microprocesor thinks the tape 
position is and what it really is are different.

Everything is analog except particle physics.

Grant KZ1W


On 2/28/2015 9:02 AM, Patrick Greenlee wrote:
> That is why it is called a stepper motor.  Its motion is stepwise, not 
> continuous, think digital not analog.  If the steps are small enough 
> and are taken rapidly enough you can closely simulate the smooth 
> turning of an analog motor. Of course an advantage of the stepper 
> motor is you can keep track of where you are by counting the steps and 
> not need a shaft encoder or other method of tracking position in a 
> system driven by an analog motor. Stepping motors make position servos 
> simpler.
>
> Patrick   NJ5G
>
> On 2/27/2015 9:09 PM, Dick Green WC1M wrote:
>> I believe the brushes Joe mentioned are the ones that connect the 
>> balun to
>> the copper-beryllium element ribbons. Nothing to do with the stepper 
>> motors
>> but another potential point of failure.
>>
>> 73, Dick WC1M
>>
>>> -----Original Message-----
>>> From: Doug Turnbull [mailto:turnbull at net1.ie]
>>> Sent: Friday, February 27, 2015 4:25 PM
>>> To: 'Joe Subich, W4TV'; towertalk at contesting.com
>>> Subject: Re: [TowerTalk] SteppIR
>>>
>>> Joe and OMs,
>>>       I do not believe a stepper motor has any brush contacts.    It 
>>> does
>> not
>>> create the rotating magnetic field in this manner.   There are 
>>> alternate N
>>> and S poles on the rotor and the magnetic field on the stator is varied
>>> N-S-N to cause rotation.    Am I wrong in my understanding?
>>>
>>>                     73 Doug EI2CN
>>>
>>> -----Original Message-----
>>> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
>>> Joe Subich, W4TV
>>> Sent: 27 February 2015 15:27
>>> To: towertalk at contesting.com
>>> Subject: Re: [TowerTalk] SteppIR
>>>
>>>
>>>   > My question: With a SteppIR beam, what is the tradeoff of the 
>>> fixed  >
>>> element spacing on gain and pattern?  Especially compared to the  > 
>>> multi-
>>> yagis-on-one-boom high end multiband antennas.
>>>
>>> There is no trade-off in gain.  Gain is almost entirely a function of
>>> boom length as long as you don't have to few elements.   For example,
>>> SteppIR antennas all show more gain on 10/12 meters than the multi-
>>> monoband yagis simply because the SteppIR antennas utilize the entire
>>> boom length on all bands where the multi-monoband antennas typically 
>>> use
>>> 60-70% of the available boom length on each band.
>>>
>>> Where the boom is "short" and the spacing is narrow, you give up 
>>> bandwidth
>>> but SteppIR compensates by retuning.
>>>
>>> When the boom is "long" and the spacing is wide you give up some F/B.
>>> For example, the 3 element SteppIR shows F/B of "only" 15 dB on 12 
>>> meters
>>> and 11 dB on 10 meters vs. 25 dB on 20 and 17 meters.  You see 
>>> similar F/B
>>> declines with the 4 element antenna.
>>>
>>> With SteppIR the trade off is increased complexity (the stepper 
>>> motors and
>>> brush contacts) while with the typical overlaid multi- monoband antenna
>> the
>>> trade off is decreased gain for a given boom length.  All of this is
>> verifiable
>>> with a few hours spent using a good antenna modelling program.
>>>
>>> 73,
>>>
>>>     ... Joe, W4TV
>>>
>>>
>>> On 2015-02-27 9:51 AM, Al Kozakiewicz wrote:
>>>> I was tempted to hijack the Mosley thread, but it should probably be
>>> allowed to die peacefully.
>>>> I discovered a few years ago that you can't ask any questions where an
>>> honest answer might be construed as a criticism on the SteppIR forums.
>> The
>>> dialog degenerates into something resembling the useless old 
>>> alt.advocacy
>>> newsgroups.
>>>> My question: With a SteppIR beam, what is the tradeoff of the fixed
>>> element spacing on gain and pattern?  Especially compared to the multi-
>>> yagis-on-one-boom high end multiband antennas.  You're pretty much 
>>> in the
>>> same territory price-wise.
>>>> Al
>>>> AB2ZY
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