"COLIN LAMB" wrote in message
hlink.net...
Well, I was trying to be helpful. Instead, I am condescending.

I have been a ham longer than 41 years, and I learn things all the time.
Sometimes, I forget simple ways to do things.

The Bird is not a model of accuracy. Accuracy is specified as a % of full
scale. I do not have my books handy, but I recall it is 5% of full scale.
If my recollection of 5% is correct, that means that it could be off (oh,
oh, here is simple math) 125 watts at full scale or 125 watts when you
are reading 500 watts. Using another Bird is not a good method of setting
the accuracy.

You have to use the dvm to check out the dummy load, anyway. If the dummy
load is off in resistance, the Bird wattmeter will not read correctly -
since it is assuming that the load is 50 ohms. I have checked dvms and
found even the cheap ones are quite accurate - much higher than the
accuracy specified for the Bird. I have also check dummy loads and found
they are often off. A friend asked me to come over because he was
measuring 3200 watts out of his amplifier and thought it was high. It
was - the dummy load was also high.

If you are interested in an accurate reading slug, then calibrating it
against another Bird slug does not make much sense - since that might be
inaccurate. Forget the surplus rf voltmeter and simply measure the heat
rise of the dummy load. That will be an exact measurement of the power
going in and yield much more accurate readings than the Bird. It will
simply take a thermometer and a bit of math. I will not detail how to do
it, because that might be condescending.

I have a number of Bird wattmeters and slugs. I use them for quick and
crude measurements - because they are handy. Before I could afford the
Birds, I designed and built my own - and calibrated them. In fact, I
wrote an article for QST in 1973 on how to build your own using ordinary
plumbing parts. They were hand calibrated and as accurate as any Bird
meter.

If, you want your meter to be calibrated like Bird would do it, send it to
them.

Colin K7FM


I "started" to reply last night and I thought I'd let Colin speak for
himself. He has. "I" personally didn't find him to be "condescending". You
have to understand something. Bird Wattmeters or ANY equipment - as you have
found "can" fail or come under question. OK - so when it does - now you're
faced with the exact predicament that you are. So - do you stop working and
wait and wait and wait until you can figure out what to do about THAT piece
of equipment, OR do you finagle another method to check the results of the
"suspect" equipment and to get a comparison reading? I can't speak for you -
but I choose option number 2. I can't afford to wait. Time is money.

As for "my" interest - though right now I have no doubts of my equipment, it
is always nice to know what to do or where to turn to remedy any problems.
I've never bothered to check into this before - regarding the bird - and
your question gave me the initiative THANKS!. I believe now I can do it
myself - BUT - if not - just do what needs to be done - bite the bullet and
have Bird do it. I've forwarded each response to my mailbox as I always do
with valid info to build my library of "Useful" information for future
reference.

Back to point number one....... When I got into Ham and 2 way radio - I
learned how to do without the fancy equipment I couldn't afford "then". That
included hooking up with those who did have it on an as needed basis. I made
mock up equipment and set ups which got me pretty far along without much
problem. An Eico 232 with an RF probe validated quite a few cheaper
Wattmeter readings. As Colin said, you have to also make sure the Dummy Load
"is" at the reference it is supposed to be OR your readings are shot in the
ass. A bad dummy load can make things look pretty goofy and if you don't
"check" it, then you're there scratching your head wondering what the hell
is going on. Now I have all that fancy stuff and am fortunate to have it -
but should it flake out - then it is back to using the other set ups until I
can get this stuff back on line.

As to Colin's article, I "think" I have it here somewhere - I recall reading
it. Pretty good article - though with the plumbing, I chuckled due to myself
not being much of a plumber! Those articles always give you room to think
and to expand - maybe to create your own way of doing things.

Just my 2 cents - taken with a grain of salt and CERTAINLY not meant
either - to be condescending.

L.

At the end of the day, thank you for your input, Colin. Your help
truly is appreciated.

I guess I was in a bit of a dour mood when I previously posted. Sorry
if I read into your comments.

73,
Jeff


COLIN LAMB wrote:
Well, I was trying to be helpful. Instead, I am condescending.

Well, time flies when you are getting old. After I wrote the last note, I
remembered that the article on home made directional wattmeters was in the
80's. I vaguely recall it was October 1983.

Today, I have all sorts of sophisticated test equipment, but still enjoy
rolling my own and calibrating it with simple equipment. Recently some of
my friends needed to measure the patterns of antennas. Although I have a
couple commercial field strength meters, I constucted a simple one then used
the signal generator to calibrate it. Once you have a calibrated standard,
you can build frequency compensated voltage dividers to allow you to measure
rf voltage with a fairly high precision.

I teach survival classes and you need to learn to use what you have. I once
demonstrated to a class that you could navigate with an old tennis shoe -
and be as accurate as with any small handheld compass - although not nearly
as quickly or as conveniently. And, I was in a map reading workshop where
we were reading a number of bearings using the pocket compass. I left my
compass in my pocket to see how I could do taking about 10 bearings with no
compass at all. I tied for first place. By simply dividing into
quadrants - by hand - you can get amazing accuracy. And, most of the people
in the class got at least one wrong answer by not thinking and using the
reciprocal.

But, I am amazed that when I learn something new it is often from some new
and inexperienced person who approached things from a different perspective
than I did.

73, Colin K7FM

Condescending?? Brother, you're one high-strung honey if you found his
advice offensive.

Secondly, you aren't the only person in this conversation that requested
info, and I for one appreciate these
little 'brush-ups' on procedures, etc.

And finally, to quote you....

"It's starting to look like I should just borrow someone else's 2,500
watt slug known to be accurate, and then just adjust the pot in mine to
match! Anyone want to lend me theirs? ;-)"

So looks like you're quite willing to make due and trust someone else's
"accurately" misaligned slug.

In conclusion....
Take a big deep breath and calm down. Your sarcasm certainly doesn't elevate
you any higher than the complaints you
yourself have.
rib



wrote in message
ups.com...
Thank you for telling me what ham radio is all about. 41 years of
ignorance now cured. And I also deeply appreciate your pointing out my
lack of effort figuring out how to use what I have. What a slackard I
have been. I'll try to mend my ways. Finally, thank you so much for
restating Ohm's law - I'll attempt to better understand it.

Ok, let's cut to the chase here, OM ... first, if I wanted to "make do"
I wouldn't have bothered to post my question, let alone invest in a
Bird. Not all of us lie down and just "make do". I really don't need
you to tell me how to set / lower my standards.

And secondly, if I'm questioning the accuracy of a Bird slug, why on
earth would I want to now rely on the accuracy of some "DVM" or
"surplus voltmeter" at the kilovolt level? It simply doesn't make
sense.

Perhaps I am over-reacting, but your attitude is clearly condescending:
all I asked was if anyone knew where I might get a slug recalibrated.
I really didn't ask what you thought ham radio is all about, nor for
you to judge my level of effort.



COLIN LAMB wrote:
"Yes, there is some good information floating around. However, it all
boils down to, in your words, having an accurate standard available. I
do not."


This is what ham radio is all about. We make do without adequate test
equipment - we just need to put a little more effort into figuring how to
use what we have.

Take a dummy load. Use a dvm to measure the dc resistance. That should
also be the rf impedance. You can determine power going into the load by
measuring the rf voltage across it. Some of the surplus voltmeters will
measure rf voltage. Or, borrow one. Knowing the rf voltage across 50
ohms,
you can calculate power. P= e squared / R.

It is likely that the linearity of the Bird is ok, even if the power
reading
is incorrect. So, once you check the accuracy at one point, you have it
for
all points.

Colin K7FM

And Amen to real men.
Kudos, Jeff.
rb

wrote in message
ups.com...
At the end of the day, thank you for your input, Colin. Your help
truly is appreciated.

I guess I was in a bit of a dour mood when I previously posted. Sorry
if I read into your comments.

73,
Jeff


COLIN LAMB wrote:
Well, I was trying to be helpful. Instead, I am condescending.

On 13 Sep 2006 13:44:56 -0700, wrote:

I have a 2,500 watt, HF slug that I don't have confidence in. Anyone
know who calibrates slugs for a reasonable fee?

Thanks.
Jeff
W8KZW

http://www.radiodan.com/ deals in new and used Bird equipment. He
might have some advice, or might do a tradeout with you for another
slug.

bob
k5qwg

Well, I went to the horse's mouth and asked Bird 1) how much, and 2)
might I drop in ...

Hello Jeff,
The cost for calibration on 2500w slug is base on Frequency Bands
The cost 2500H is $100 the cost for 2500A; B; C; D; E AND J is
$200
Regarding walk in, no we do not Calibrate walk-in basis.

Best regards,

Not unreasonable, I think, for commercial concerns, given the time it
likely takes to do this and the investment they have made in
professional-grade equipment. A bit steep for me for casual, amateur
use though.

.... at least they were nice.

73,
Jeff

wrote:
Well, I went to the horse's mouth and asked Bird 1) how much, and 2)
might I drop in ...

Hello Jeff,
The cost for calibration on 2500w slug is base on Frequency Bands
The cost 2500H is $100 the cost for 2500A; B; C; D; E AND J is
$200
Regarding walk in, no we do not Calibrate walk-in basis.
=============================================
Re Bird calibration: When my company had all test equipment out for
calibration for ISO-9001 certification, I included an out-of-tolerance
Bird slug with one of our 43 wattmeters. The meter 'passed', & still
had the 'bad' slug in it. I queried the tech, & he said they only check
the 30MA meter - not the slugs.

A ham who ran/runs a used test eq. biz in the MD-DC-VA area used to
make the local hamfests. He would take bad & out-of-calibration slugs
in trade, & repair them in his shop. He found a source for the [then]
scarce diodes, + did a neat job of removing the drive pins that secure
the face plates. If I could remove them neatly, I'd calibrate one of
mine. At one hamfest, a CBer walked up & asked him if he had his 25KW
slug yet. I started to follow him back to his car, & report his tag #
to the FCC.

BTW, I have some extra VHF/UHF slugs, & need a few HF slugs.

73,
jack_son73