I have never seen a reason to spend big money on
a Bird wattmeter but I do have a question.
What exactly is inside the various slugs
that one must use with this meter ?
Art

On 14 Sep 2003 12:35:05 -0700, (Art Unwin KB9MZ)
wrote:

I have never seen a reason to spend big money on
a Bird wattmeter but I do have a question.
What exactly is inside the various slugs
that one must use with this meter ?
Art

Hi Art,

A loop, at least one cap, a diode, at least one resistor.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On 14 Sep 2003 12:35:05 -0700, (Art Unwin KB9MZ)
wrote:

I have never seen a reason to spend big money on
a Bird wattmeter but I do have a question.
What exactly is inside the various slugs
that one must use with this meter ?
Art

Hi Art,

A loop, at least one cap, a diode, at least one resistor.

73's
Richard Clark, KB7QHC

The little network, along with the section of coax line inside the main
housing, forms a directional coupler. A Bird 43 (or similar, but the 43's
are readily available, used, on eBay) is about the cheapest way to get
answers about the design and performance of your antenna and transmitter
system.

And if you think a Bird 43 is big money, you ain't seen nothing yet!

Ed
WB6WSN

In article , Art Unwin
KB9MZ wrote:

I have never seen a reason to spend big money on
a Bird wattmeter but I do have a question.
What exactly is inside the various slugs
that one must use with this meter ?
Art

A coupling network and a diode are inside the slug. Slugs are
calibrated by twiddling (literally) components inside the slug, and
then putting the label on the front of the slug.

You can find the meters on eBay, but you need to be careful buying the
slugs sight unseen -- some of the lower-power slugs can be thrown out
of cal by being dropped (on a hard surface).

An easy way to check a slug is to put two high quality 50 ohm loads in
parallel (use a "T") on the output of the meter. Bird loads are also
easy to find on eBay and swap meets -- I have one that's probably 40
years old, and a newer one, only 20 years old.

Try and keep your readings midscale for best accuracy. Put the
shorting slug in the meter when the meter isn't in use, or turn the
slug so the arrow points up at the meter to protect the movement.

The Bird is a wonderful, stable design that's simple and well
understood. You can get fancier (from Bird, among others), you can get
more accurate (my old HP), but it's hard to get simpler.

On Sun, 14 Sep 2003 14:31:08 -0700, "Ed Price"
wrote:
The little network, along with the section of coax line inside the main
housing, forms a directional coupler. A Bird 43 (or similar, but the 43's
are readily available, used, on eBay) is about the cheapest way to get
answers about the design and performance of your antenna and transmitter
system.

And if you think a Bird 43 is big money, you ain't seen nothing yet!

Ed
WB6WSN

Hi Ed,

I am quite familiar with the Bird 43. A useful instrument on the
bench, more appropriate in the field. The URM-120 by Sierra is far
more robust and always keeps its calibration. I have used
instrumentation that is far more expensive and I have used
instrumentation that was far cheaper. I have calibrated them all.

For the amateur, a cheap Radio Shack CB SWR meter is more than
adequate, and if it is not perceived to be, is easily tailored to fill
that shortfall of perception. It shouldn't cost anyone more than $20
(mostly for the meter) to build a very good one. There are scads of
designs available, and all revolve around the same assembly of simple
components I described for Art. If any trick is involved, it is close
attention to dimension and wavelength.

Choice in SWR meters is almost akin to preference in tie color, a
personal matter.

73's
Richard Clark, KB7QHC

artie wrote:

The Bird is a wonderful, stable design that's simple and well
understood. You can get fancier (from Bird, among others), you can get
more accurate (my old HP), but it's hard to get simpler.

I use a homebrew directional coupler (see QEX for
March 1995) for everyday use, and a brand new,
well preserved (in a closet) Bird 43 as a
reference instrument. At full scale it is specifed
as accurate within +/- 0.5 db, which is plenty
good enough for me.

Bill W0IYH

Art Unwin wrote:
"What exactly is inside the various slugs that one must use with this
meter?"

73 Amateur Radio had an article, "Calibration and Repair for Bird
Wattmeter Elements" in its April 1989 issue by Francis Kelson, K2KSY.

K2KSY`s plug-in element diagram is more complete than that given by Bird
under the topic, "Thruline Principle" in my Bird catalog. Bird may have
been guarding proprietary information in 1989 when my catalog was
issued.

The Bird Model 43 accuracy is specified as + or - 5% of full scale in
the catalog. So, a "slug" which would cause nearly full scale deflection
should probably be used for accuracy.

Accuracy results from the careful, rugged construction and calibration
of the Bird.

Bird says: "Broadcasters may want to order two identical Elements at the
same time and keep one in a safe place after recording the meter
readings obtained by each. If a question arises about recalibration
(e.g. in case an Element has been dropped on a cement floor), a quick
comparison with the original twin could save time, effort and
inconvenience of shipping the whole wattmeter back for a checkup. For
better resolution of low reflected power levels, we recommend a second
Element 1/10 the power of the forward Element."

From the above, Bird seems to advise broadcasters initially buy 4
Elements.

Richard Clark, a metrologist, occasionally disparages Bird`s accuracy on
this newsgroup. I`m no metrologist, but have experience with many Bird
43`s and have seen them to be highly repeatable and exchangeable. They
usually read what you would expect and they read what you determine the
power to be by other means. I doubt that cheap meters come close to the
Bird`s reliability. I think the Bird Model 43 is a good value.

Best regards, Richard Harrison, KB5WZI

"William E. Sabin" sabinw@mwci-news wrote in message ...
artie wrote:

The Bird is a wonderful, stable design that's simple and well
understood. You can get fancier (from Bird, among others), you can get
more accurate (my old HP), but it's hard to get simpler.

I use a homebrew directional coupler (see QEX for
March 1995) for everyday use, and a brand new,
well preserved (in a closet) Bird 43 as a
reference instrument. At full scale it is specifed
as accurate within +/- 0.5 db, which is plenty
good enough for me.

Bill W0IYH

Why would a ham operator have a need for such accuracy ?
Isn't consistency enough ? For ensurance of not exceeding
the power output for those who want to equal the max then
a scope would be the way to go. For those that build then
there is a need for accuracy and bragging rights are fully
earned. Seems like this falls into the same catagory of
'I have six elements where you have only five'
Art

Why would a ham operator have a need for such accuracy ?
Isn't consistency enough ? For ensurance of not exceeding
the power output for those who want to equal the max then
a scope would be the way to go. For those that build then
there is a need for accuracy and bragging rights are fully
earned. Seems like this falls into the same catagory of
'I have six elements where you have only five'
Art

'need' is maybe too strong a word, but in general, i'll buy a more precise
meter if i can afford it, rather than a less precise one. your tools are
your eyes. if you can't measure it, you can't improve it.

bird owner

isn't the power rule about input?
sam

--
toys:
diesel BMW motorcycle, homebuilt electric motorcycle, gold wing trike, honda
gyros, dodge diesel dualie, fiat osca 1500 cabriolet,
W3CYO/R, 145.49, 224.40, 443.300 mhz. repeaters.


"Art Unwin KB9MZ" wrote in message
m...
"William E. Sabin" sabinw@mwci-news wrote in message
...
artie wrote:

The Bird is a wonderful, stable design that's simple and well
understood. You can get fancier (from Bird, among others), you can
get
more accurate (my old HP), but it's hard to get simpler.

I use a homebrew directional coupler (see QEX for
March 1995) for everyday use, and a brand new,
well preserved (in a closet) Bird 43 as a
reference instrument. At full scale it is specifed
as accurate within +/- 0.5 db, which is plenty
good enough for me.

Bill W0IYH

Why would a ham operator have a need for such accuracy ?
Isn't consistency enough ? For ensurance of not exceeding
the power output for those who want to equal the max then
a scope would be the way to go. For those that build then
there is a need for accuracy and bragging rights are fully
earned. Seems like this falls into the same catagory of
'I have six elements where you have only five'
Art