Don't be ashamed of buying stuff, people. I just paid $65
for a tuning pulser. I haven't taken the cover off, but
odds are that its nothing more than a relaxation oscillator
and a rotary switch (to control the duty cycle). Still my
free time is in short supply, so I try focus on building
stuff where I will learn something new as that has a
potential return on investment and is more enjoyable
that doing the same thing over and over again.
Modifying equipment is also a good way to learn
how it works and build up skills without actually having
to layout every board and fab every little detail.
73 de Mike, W4EF.......................
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "'towertalk'" <towertalk@contesting.com>
Sent: Thursday, November 18, 2004 12:03 PM
Subject: Re: [TowerTalk] 80m 4Square Comtek box
> At 02:23 PM 11/18/2004 -0500, Tom Rauch wrote:
> > > Actually, there is enough information in ON4UN's book for
> >a
> > > competent individual to build a hybrid style (quadrature)
> > > phasing unit without much more than an MFJ-259B. Of
> >course
> > > a good scope and current probes would help if one wanted
> >to
> > > optimize the unit.
> >
> >By the time most people did all that, they would be better
> >off just buying the Comtek. Retail parts aren't cheap or
> >easy any longer.
>
>
> I'll second that...
> Let's see..
>
> Knowing the values is easy. for 50 ohms, 3.8MHz, you want L=2.09 uH,
C=419pF
> The schematic is simple, too.
>
> Then, you can engage in a few hours of design time to find an appropriate
> core and design the inductor. (remember, it has to handle a kilowatt)
> The caps are catalog parts (although you need to make sure they have the
> right current ratings, etc.), so it won't take long to find them.
> Then, you'll need to select some appropriate relays, a decidely
non-trivial
> process, since RF relays that handle a kilowatt are quite pricey, so
you're
> going to want to use some other kind.
>
> Order everything (after rummaging through the junk box) you need.
>
> I'd wag the parts cost at around $100-200 (but it could easily be more...
> suitable non-surplus relays are probably $10 each in the catalog, the caps
> will be fairly inexpensive, cores are a couple bucks, but you have to
> consider things like enclosures, connectors, etc.)
>
> Wait 2 weeks (because you can't really work on it during the week).
>
> Now, spend some time winding that inductor, figuring out how to assemble
> it, put it into a box, etc. It's probably a nice 2 day job. And, if you
> have the time and tools, it would be enjoyable.. a nice combination of
> mechanical engineering and electronics.
>
> But all the same, if you paid yourself something like $8/hr, you'd
probably
> spend 20 hours on the whole project, so the labor cost is $160.
> That's a pretty unrealistic labor cost. Either you have the time to spend
> on it, in which case the time is free, or you're busy with lots of other
> things, in which case the time is infinitely expensive.
>
> Hmm.. or, just buy the Comtek box for $350. Not a bad deal.
>
_______________________________________________
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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