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KG6AIK
11-30-2011, 06:46 PM
I need a wattmeter that covers 500khz to 30mhz there does not seem to be any commercially available wattmeter that covers this frequency range. Could I homebrew one? If so where could I find the plans and schematics.

WA7KKP
12-01-2011, 12:25 AM
Older ARRL handbooks had a directional wattmeter homebrewed from copper drain pipe. The trick is to do a good enough job on the transmission line section and the pickup loop to minimize any reflections. If you don't believe me, take a close look at the Bird 43 wattmeter after pulling the slug out.

Or you can do the simpler thing -- find an RF ammeter. I had a 0-2a Weston, mounted in a Mini-box, with very short leads to the SO-239 jacks. Using ohm's law you can determine power output into a dummy load; I found it accurate even at 2 meters. No muss, no fuss.

Gary WA7KKP

KD8OUR
12-04-2011, 04:22 AM
the current antenna book from ARRL does indeed have instructions. easy to make a watt meter forward and reflected.
easy in that it can be done, but its outcome is going to depend on attention to detail, time and effort. the parts are easy to get and as state above uses common copper pipping. i am sure there are other methods of construction. most will be somewhat similar.
a good project to learn, but for the time i think i would just buy a meter and be done with it. most meters are cheap, and do all the extras. this might be a good project to convert, repair or update an old meter.

G0HZU
12-04-2011, 11:18 AM
Can you provide more info?
eg power level and wanted accuracy.

Also will you be looking to use it to measure fwd/reflected power?

If I assume toughest case that you want to run >1kW and you want good accuracy then it might be safest to split the range and make one meter for the bottom end of the band and either buy or make one for the regular HF bands.


This is because if you are running a big amplifier that needs accurate VSWR measurement (eg you want to measure 1.8:1 +/-0.1) then you need to make a meter with very high directivity.

eg >33dB directivity to get you into the ballpark for that accuracy. I've not tried to make directional couplers at these power levels and one thing that would concern me would be getting high directivity across 500kHz to 30MHz using big transformers rated at >1kW.

However, someone in the US may have already successfully made one as you have high legal power limits over there :)

K5UOS
12-04-2011, 03:03 PM
I need a wattmeter that covers 500khz to 30mhz there does not seem to be any commercially available wattmeter that covers this frequency range. Could I homebrew one? If so where could I find the plans and schematics.

This article below is a one place to start. I have built several of these particularly for use in antenna tuners. I used them primarily for SWR but good results for power measurement can be developed by calibration with an accurate commercial meter...i.e. borrow a good meter from someone.

Aug 1983 - QST (Pg. 35)

Beginner's Look At RF-Power Measurement, A
Author: Demaw, Doug, W1FB/8
http://p1k.arrl.org/pubs_archive/75824

There are other sources for this design. The original design is by W. Bruene, a Collins engineer. The design is often called a Bruene bridge and variations can be found on the web. I built my first meter from schematic in Solid State Design for the Radio Amateur by W1FB and W7ZOI.


Don, K5UOS

W9GB
12-04-2011, 03:36 PM
I need a wattmeter that covers 500 kHz to 30 MHz.
There does not seem to be any commercially available wattmeter that covers this frequency range.

Really?
There are several offerings that cover 1.8 MHz to 30 MHz (160 to 10 meters), the Diamond SX-100 is one commercial product (off-shelf, assembled).
Surplus Bird 43 units have been plentiful over the past decade, largely due to cellular/mobile consolidation/mergers/updates.

What RF power levels (measured in Watts) are you planning ?

Do you really require coverage from 550 kHz to 1.7 MHz ?? Which is the commercial AM broadcast band in North America.

IF you are looking for a "Kit" ... the Oak Hills Research WM-2 kit (QRP wattage levels) has been very popular.
http://www.ohr.com/wm2det.htm

The photos on that WM-2 kit page -- shows you how few parts are required --
as well as how easy to DIY build.

80138 80139

G0HZU
12-04-2011, 11:13 PM
I had a look at the circuit of that WM-2 QRP meter and I must say it's a very neat little design :)

It has a compensated diode detector operating up into the linear region. The compensation puts it a class above many QRP meters and I'd go as far as saying I would rate this meter above a Bird 43 for QRP power levels especially in terms of operation over temperature and accuracy at lower meter deflections. (because the bird detector is uncompensated)

WB5WPA
12-07-2011, 07:02 PM
I need a wattmeter that covers 500khz to 30mhz there does not seem to be any commercially available wattmeter that covers this frequency range. Could I homebrew one? If so where could I find the plans and schematics.

I didn't see that this had been mentioned:

"This design is applicable for small or high powers, from 100 kHz (or less) to 50 Mhz, from miliwatts to kilowatts, depending on the selected components."

http://f1frv.free.fr/main3h_SWR_Bridges.html


This is a good read too; note especially the discussion on his directional coupler design:

http://www.telepostinc.com/Files/phipps-1.pdf


Note the LP-100A is available from here: http://www.telepostinc.com/lp100.html


I came across these sites while doing a power meter literature/paper search the least few weeks.

Jim de WB5WPA

AD6KA
12-11-2011, 03:20 AM
Fox Delta, Elecraft, and Ten Tec all offer neat
Wattmeter/SWR kits. The Elecraft and Fox Delta
models are PIC based with LCD readouts.
Fox Delta offers several models including high power
and VHF/UHF models. All are very easy builds,
but Fox Delta does not supply much (if any) customer
support should you need it.
http://www.foxdelta.com/products/swr.htm

[URL=" http://www.tentec.com/products/SWR-Bridge-Wattmeter-Kit.html"]
http://www.elecraft.com/manual/MiniModule%20WM1%20AF1%20AT1%20Data%20Sheet%202006 a.pdf
73, Ken AD6KA