Modifying Wattmeter Slugs for QRP

[Arthur Delibert]

I have a Bird wattmeter that I'd like to use with QRP rigs.  As best I can tell, though, Bird did not make slugs smaller than 50 watts for the 2-30 MHz range.

There is a website that discusses how to open a Bird slug and modify it for a different power level and/or frequency range.  [http://www.hayseed.net/~jpk5lad/BIRD%20Slugs/birdslug1.htm]

I'm wondering if anyone has tried to modify, say, a 2-30MHz/50-watt slug for 10 watts and if so, any experience to share?  What was the right resistor value?  How was the linearity of the meter with the modified slug?

Thanks for any experience or insights.

Art Delibert
KB3FJO
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[N8LP]

Before you open it up, you might want to see if you can find some
documentation on the Model 4410A multi-range meter. I have one, and it
has switchable scales from 0-2W to 0-1000W using a single 4410-3 slug.
It has an amplifier in it with precision dividers I think. Much of the
Bird stuff is searchable in patent apps if you want to figure out how
they did things.

You might want to see what's inside this sensitive slug, as that's the
key to the multiple scales.

Larry N8LP



Arthur Delibert wrote:

>I have a Bird wattmeter that I'd like to use with QRP rigs.  As best I can tell, though, Bird did not make slugs smaller than 50 watts for the 2-30 MHz range.
>
>There is a website that discusses how to open a Bird slug and modify it for a different power level and/or frequency range.  [http://www.hayseed.net/~jpk5lad/BIRD%20Slugs/birdslug1.htm]
>
>I'm wondering if anyone has tried to modify, say, a 2-30MHz/50-watt slug for 10 watts and if so, any experience to share?  What was the right resistor value?  How was the linearity of the meter with the modified slug?
>
>Thanks for any experience or insights.
>
>Art Delibert
>KB3FJO
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>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
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>Help: http://mailman.qth.net/subscribers.htm
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>
>
>
>  
>

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[Sandy W5TVW]

Bird makes (or made?) a model 4410 wattmeter that will do what you want.
It looks identically to a model 43, except it has a single knob "range" switch
on it.  The "ranges" depend on the slug in use.  Mine has a 1 KW max.
2-30 Mhz slug, which yield ranges from 0-1 watt to 0-1000 watts with
a 1 and 3 scaling scheme. (1-3-10-30-100-300-1000 watts in this case).
Very handy for low power stuff.  VHF/UHF elements are available for it
that go down into milliwatt ranges.  It has a built in solid state amplifier that
is run by a common 9v. transistor radio battery.
They ain't cheap!  When I bought this one years ago it was around $500
less elements.  The elements were around $100 each at that time.
I only have two elements for it. 1 KW 2-30 mhz and 1 kw 144-520 Mhz.
(Both give the 1 watt to 1000 watt full scale ranges as per note above.)
I sure can't afford to buy elements for it now!  (Was using it on the job
when I bought it so it was a "tool" expense for income tax purposes.)
73,
Sandy W5TVW
----- Original Message -----
From: "Arthur Delibert" <[hidden email]>
To: <[hidden email]>
Sent: Friday, February 03, 2006 10:26 PM
Subject: [Elecraft] Modifying Wattmeter Slugs for QRP


| I have a Bird wattmeter that I'd like to use with QRP rigs.  As best I can tell, though, Bird did
not make slugs smaller than 50 watts for the 2-30 MHz range.
|
| There is a website that discusses how to open a Bird slug and modify it for a different power
level and/or frequency range.  [http://www.hayseed.net/~jpk5lad/BIRD%20Slugs/birdslug1.htm]
|
| I'm wondering if anyone has tried to modify, say, a 2-30MHz/50-watt slug for 10 watts and if so,
any experience to share?  What was the right resistor value?  How was the linearity of the meter
with the modified slug?
|
| Thanks for any experience or insights.
|
| Art Delibert
| KB3FJO
| _______________________________________________
| Elecraft mailing list
| Post to: [hidden email]
| You must be a subscriber to post to the list.
| Subscriber Info (Addr. Change, sub, unsub etc.):
|  http://mailman.qth.net/mailman/listinfo/elecraft
|
| Help: http://mailman.qth.net/subscribers.htm
| Elecraft web page: http://www.elecraft.com
|
|
|
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