----- Original Message -----
From: <K3BU@aol.com>
To: <towertalk@contesting.com>
Sent: Saturday, February 21, 2004 6:35 AM
Subject: Re: [TowerTalk] Steppir tuning noise
> In a message dated 2/20/04 9:44:39 PM Eastern Standard Time,
> jimlux@earthlink.net writes:
> >>Inexpensive
> run of the mill steppers (with decent temperature ranges, etc.) are
probably
> around $50, brand new, in big quantities. Shielded steppers with the
fancy
> connectors are more like $500 or $1000. Fluidmotion would have a hard
time
> selling $10,000 antennas, and I suspect that folks would balk at spending
> dollars/foot for high performance shielded control cables as well.<<
>
> You don't need $500 to put shield over the leads coming from the motor and
to
> use shielded cables. We have been doing it for $5 with ignition noises in
> mobile installations where thousands of volts and real sparks are
involved. Dog
> food can and piece of braid can do miracles.
That dog food can and shielded wire is just fine for a one-off solution to a
particular installation. How many hours did you spend finding the right size
can, cutting it to size, soldering braid on, etc.? If you're in business
selling things, these are non-zero cost.
If you want to buy an off the shelf product, there's basically two flavors:
unshielded (cheap) and shielded (very expensive) because there's not much
demand for large quantities of a "sort of shielded" product. People who
have real problems with EMI/EMC concerns in harsh environments, and have
real budgets, aren't going to quibble over a few hundred bucks, when it
might cost several engineer days to track down the problem.
>
> Also instead of square wave hard pulses, something closer to a perfect
keying
> waveform (or sine wave) might do to minimize the harmonics generation and
> noise way up in the HF frequencies.
Indeed.. there is a LOT of work in the PWM world these days on minimizing
narrow band noise from switchers, by using dithering or spread spectrum
techniques to spread the power out. May not reduce the total noise power,
but certainly makes it less obvious on a spectrum analyzer.
However, all this nifty stuff costs time and money to figure out. If you're
a manufacturer, trying to produce a reasonable quality product at a
reasonable price, you've got to make some decisions. If you're a ham,
investing your own time for free, on your own installation, you can afford
to spend a lot of time optimizing all your EMI/EMC problems. Odds are,
though, that the solutions you come up with, for your installation, may not
be able to be manufactured and sold at a price other hams are willing to pay
(assuming you don't want to work for free), and given the peculiar nature of
interference, your product may not even work.
>
> Nothing is impossible. I managed to reduce my 28 MHz second harmonics from
> the 14 MHz exciter after going through 2 kW linear, into tribander by 20
dB. The
> same helped 10m QRM to Channel 2 TV. Some PI-L filtering, stubs and link
> coupled network can do "miracles".
How many hours of work did it take to do the reduction? make sure you count
the time researching filter designs, trying various approaches, tuning the
stubs, etc.. Figure your time at a cheap $50/hr, take the parts cost, using
components purchased new from catalogs, and double it (to cover shipping,
assembly, etc.) . How much would your filtering system cost? Would you be
willing to guarantee that it would work for any ham who bought it? How
tuned is it to your particular installation?
>
> It would be interesting to see what steps were taken by SteppIR to reduce
the
> noise problem. Is ANY filtering/suppression used? Again, I do not have
their
> antennas, just saw the pictures and judging by the comments.
Perhaps someone who knows will answer. If "I" were making such a product,
I'd probably take some notional efforts, on general principle, but not worry
about noise during the tuning process. I'd spend my time making sure that
the tuning algorithm didn't result in tuning actitivity when not wanted (for
instance, making "smart" decisions about when to declare that a retune is
needed). Most people don't mind the couple seconds of mad relay clicking on
an autotuner as it attempts to match as you tune around. The latest crop of
autotuners have frequency memories to reduce even this.
>
> 73 Yuri, K3BU.us
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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