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JLuckey(at)pacbell.net
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 Posted: Wed Mar 28, 2012 6:53 pm Post subject: Should I Buy an SWR Meter? |
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Bob,
I’m building an RV7A and I’m into electronics. Should I buy an SWR meter? I know it can help me optimize the antenna systems for my com transmitters and I enjoy geeking-out on things like this.
Can an SWR meter help w/ the setup of VOR receivers as well. Can it help me w/ the installation of the Bob Archer antenna for VOR? (I thought that SWR was used primarily for measurements w/ transmitters).
Is there a “Big Dummies Guide to Antenna Theory” book available? I’d like to squelch some of my ignorance in this area.
(so many questions, so little time…)
Thanks,
Jeff Luckey
Direct Connection Systems
www.DCSIT.com
949-645-8832
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Thu Mar 29, 2012 7:48 am Post subject: Should I Buy an SWR Meter? |
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At 10:52 PM 3/28/2012, you wrote:
Bob,
I’m building an RV7A and I’m into electronics. Should I buy an SWR meter? I know it can help me optimize the antenna systems for my com transmitters and I enjoy geeking-out on things like this.
Just how MUCH do you enjoy it? I have two shops and
a large inventory of tools and materials . . . MOST
of which has not been touched in months to perhaps
decades. NEED? Obviously small. Potential for addressing
a design goal? Obviously great . . . but every project
usually requires some purchases . . . of materials and
the occasional tool.
Any borrow/buy advice offered by any of us will be
polluted with personal perceptions of need/usefulness.
I'd suggest that it comes down to expendable cash.
Suppose you DID run off and spend $100 on a nice VHF
SWR instrument. Suppose further that 10 years from
now you find that you've used the device perhaps a few
times at the outset but not once in the last 8 years?
How would you judge your return on investment then?
Can an SWR meter help w/ the setup of VOR receivers as well. Can it help me w/ the installation of the Bob Archer antenna for VOR? (I thought that SWR was used primarily for measurements w/ transmitters).
It is true that ALL such instruments need to excite the
antenna or feed line at the frequency of interest. But
that excitation can come from a variety of sources
depending on the sensitivity of the instrument.
SWR meters like the Red Dot device we've discussed
recently need a watt or so. Antenna analyzers like the
MJF-259 (and close cousins) have internal signal generators
to supply the necessary excitation.
In the case of your VOR antenna, I'd suggest using
a hand held and some device like the Red Dot SWR
meter. You can tune for optimum performance at the
lowest COMM frequency which is at the upper end of
the VOR band. This would be great verification of
gross performance and more than adequate for VOR
reception.
Is there a “Big Dummies Guide to Antenna Theory” book available? I’d like to squelch some of my ignorance in this area.
Hmmmm . . . the short answer is YES. But the constellation
of antenna styles and design goals is . . . shall we say . . .
HUGE? I have antenna books on the shelves wherein
98% of the pages offered nothing useful to my professional
activities . . . but the 2% of useful stuff was very
helpful. I'm reluctant to suggest specific titles.
Do some 'net searches on VHF antennas and SWR. Look over
the construction articles, techniques for adjusting,
etc. You will probably learn more that is useful to your
aviation interests by playing with antennas in the shop
that are also destined to go on your airplane.
Remember this picture? I don't even recall what we were
discussing on the List but I did this little 1/4-Comm antenna
setup on a sheet of copper clad right here in the shop.
But I'm confident that we learned or demonstrated something
interesting or useful.
[img]cid:.0[/img]
Then there is the constellation of grey-matter here on
the list that is accessible to you. I've been gathering
the stuff together to do a back-yard-antenna-range evaluation
of performance for BALUN versus NOBALUN. During this
exercise I'll explore the notion that a Pawsy stub
does behave like transmission line with some small dielectric
effects for velocity factor and should be mechanically shortened
to center it up at the frequency of interest.
I'll document that experiment and post it to AeroElectric.com
(so many questions, so little time…)
You got that right. Education is expensive. It goes far beyond
the cost of tuition, tools and materials. The big expense is
$time$. Hence the notion that participation in activities like
the AeroElectric-List can and should offer significant reduction
in the expenditure of $time$. This applies to both academic science
and practical arts of our shared interests.
Buy an SWR meter? You bet! But with the caveats I've cited
above tucked into your hip pocket.
Bob . . .
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