Callsign

# Thread: looking for swr/power meter kit

1. Ham Member
Join Date
Jul 2010
Posts
136

## looking for swr/power meter kit

Anyone know of a good kit thats not for qrp use only??

2. Ham Member
Join Date
Mar 2006
Location
Newcastle, NSW, Australia
Posts
2,774
You could easily modify many QRP kits by only changing the coupler.

Suppose the kit uses 10 turns on a toroid. That gives a 20dB coupler since the coupling ratio is proportional to the square of the turns ratio.

10 squared = 100; 100 times is 20dB.

So, say, 10 watts on the through line produces 100 milliwatts to the detection circuitry.

Suppose we now wind 32 turns on the toroid. 32 squared = 1000; 1000 times is 30dB.

Now 100 watts on the through line produces 100 milliwatts to the same detection circuitry.

It only remains to add a zero or two as appropriate to the analog meter scale; this could even be done "mentally" by remembering to multiply all power readings by ten.

SWR is a ratio so no change to the SWR scale would be required.

If the original coupler has more or less than ten turns, use the above simple maths to calculate a new coupler; for instance, an original 12-turn coupler will require 38 turns for a x10 change.

A x10 change is not mandatory; it can be anything but x10 gives simple meter re-scaling.

And, if the extra turns won't fit on the core used originally (the NorCal kit uses a "pig-nose" core for its "Stockton" (Sontheimer & Fredrick actually) coupler and 32 turns might not fit) just use a larger core or, in the case of the NorCal coupler, two small toroids or beads of the same material.

3. Ham Member
Join Date
May 2001
Posts
192
Kind of pricey (\$159) but Ten-Tec has one:
http://www.tentec.com/index.php?id=330

But, for that price, I'd recommend the factory-built Autek WM-1:
http://www.autekresearch.com/wm1.htm

73,
Mel - KS2G

4. Ham Member
Join Date
Mar 2007
Posts
3,705
I can highly recommend the LP100 kit:
http://www.telepostinc.com/lp100.html

There's no need to play with turns ratios - the standard coupler covers 50mW to 3kW.

There's also an excellent Yahoo support group:
http://groups.yahoo.com/group/lp-100/

But not cheap

Steve G3TXQ

5. Ditto on the LP100 - I use it for everything from my legal limit amp to measuring power out of the K3 xtransverter port (in direct mode w/o the coupler).

Steve
KV6O

6. Ham Member
Join Date
Mar 2007
Posts
3,705
One of the nice things about the LP100 is its ability to operate as a digital field strength meter. It interfaces easily to other software to automatically produce polar plots such as this:

Incidentally, the "skew" in the rearward pattern was caused by a common-mode issue I was investigating.

Steve G3TXQ

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•