At the risk of thoroughly boring you all, I'll summarize the position to
date. I have a good workshop with power tools and I like metal bashing and
am quite happy with PCBs. I even have an electronic calliper so can measure
thickness accurately. However, my eyes will not allow very fine work like
SMD. I am looking to build an SWR meter using two 1 mA meters, one for
forward and one for reverse. I am looking for a practical (non-theoretical)
article on how to build one. I am wondering if there is one the ARRL
handboook before I go to the exp-ense of buying one here in Australia. Most
of the beautifully argued theory on here is way way beyond me. Any pointers
to a suitable article?

"Jim Lux" wrote in message
...
Suzy wrote:
"Richard Clark" wrote in message
...

On Fri, 1 Feb 2008 06:12:14 +1100, "Suzy" not@valid wrote:


I suppose there's still the possibility of cutting the trace a bit
narrow on purpose and adjusting the impedance by adding a grounded
plate above the board. It could be spaced an adjustable distance away
by mounting it with threaded rods (long screws), and adjusted to make
the traces 50 ohms.

**But how do you check that in a workshop with no test gear?

This is called residual SWR in a reflectometer. You load it with a
known good load, and what SWR you find (or what is exhibited by the
two meters) inhabits the reflectometer itself. Then you flip it over
and apply your source into the goesoutta with the known load on the
comesinna. You then proceed to reduce the residual SWR in both
directions.

Finding a good load is another matter, and I reported one (a precision
RF resistor) with specific characteristics here last week. Consult
the thread "RF Power Resistors from Caddock."

All of $10-$20 to accomplish.

73's
Richard Clark, KB7QHC


I'm in Australia!

http://www.caddock.com/ has a link to their Australian distributor
(granted, they may have some punitive minimum order).

A begging letter to Caddock for a sample might work?

Or, do the big mailorder companies ship to Australia (the parts are in the
few bucks range.. postage and shipping could be more)

Thanks very much for that, but I am hoping to get a Bird Termaline 50W dummy
load, which I hope will enable me to progress. Thank you all for holding
this floury (not flowery!) hand.

"Suzy" not@valid wrote in message ...
At the risk of thoroughly boring you all, I'll summarize the position to
date. I have a good workshop with power tools and I like metal bashing and
am quite happy with PCBs. I even have an electronic calliper so can
measure thickness accurately. However, my eyes will not allow very fine
work like SMD. I am looking to build an SWR meter using two 1 mA meters,
one for forward and one for reverse. I am looking for a practical
(non-theoretical) article on how to build one. I am wondering if there is
one the ARRL handboook before I go to the exp-ense of buying one here in
Australia. Most of the beautifully argued theory on here is way way beyond
me. Any pointers to a suitable article?
And further to that, I am hoping to shortly get a Bird Termaline 50W dummy
load, so I'll have something to work with!

"Suzy" not@valid wrote in :

Suzy, if you see a Revex W560 going on VKHAM for $100 or so, it is a
good buy. It has HF to 70cm (two independent couplers, ie four coax
connectors), and works pretty well.

N type on the VHF/UHF coupler, UHF type on the other coupler.

For a dummy load, the market was flooded with terminations from 25W
to about 60W that had been scrapped from AMPS base station equipment,
and they were sold at hamfests for $20 or so, you may find them if
you look around.

N type.


Owen

Thanks Owen. BTW, what type of coax connector? Not PAL surely!

No, but they are not all that bad. Almost no one manufactured VHF land
mobiles here with UHF connectors, but they did use PAL (Belling & Lee)
once (Pye Reporters for instance).

Owen

Jim Lux wrote in news:fntlce$h96$1
@news.jpl.nasa.gov:

http://www.caddock.com/ has a link to their Australian distributor
(granted, they may have some punitive minimum order).

A begging letter to Caddock for a sample might work?

Or, do the big mailorder companies ship to Australia (the parts are in
the few bucks range.. postage and shipping could be more)




Suzy,

I had a look at Farnell (au) for these type of resistors recently
(Caddock are not the only maker).

My recollection is that a 100W resistor is likely to be good for 50W -
60W in a practical application, and they were about $28 ea + $12
shipping, and IIRC minimum order quantity was one.

That is not to recommend them for a simple accurate load for 70cm.

Owen

"Owen Duffy" wrote in message
...
Jim Lux wrote in news:fntlce$h96$1
@news.jpl.nasa.gov:

http://www.caddock.com/ has a link to their Australian distributor
(granted, they may have some punitive minimum order).

A begging letter to Caddock for a sample might work?

Or, do the big mailorder companies ship to Australia (the parts are in
the few bucks range.. postage and shipping could be more)




Suzy,

I had a look at Farnell (au) for these type of resistors recently
(Caddock are not the only maker).

My recollection is that a 100W resistor is likely to be good for 50W -
60W in a practical application, and they were about $28 ea + $12
shipping, and IIRC minimum order quantity was one.

That is not to recommend them for a simple accurate load for 70cm.

Owen

But hopefully the Bird Termaline 50W model 8085 will do the job?

Suzy wrote:
At the risk of thoroughly boring you all, I'll summarize the position to
date. I have a good workshop with power tools and I like metal bashing and
am quite happy with PCBs. I even have an electronic calliper so can measure
thickness accurately. However, my eyes will not allow very fine work like
SMD. I am looking to build an SWR meter using two 1 mA meters, one for
forward and one for reverse. I am looking for a practical (non-theoretical)
article on how to build one. I am wondering if there is one the ARRL
handboook before I go to the exp-ense of buying one here in Australia. Most
of the beautifully argued theory on here is way way beyond me. Any pointers
to a suitable article?




One might find that you can BUY a surplus directional coupler for 440MHz
fairly cheaply. Check Ebay, etc.

Then it's just a matter of wiring up electronics to the coupled ports.

Suzy wrote:
"Owen Duffy" wrote in message
...

Jim Lux wrote in news:fntlce$h96$1
:


http://www.caddock.com/ has a link to their Australian distributor
(granted, they may have some punitive minimum order).

A begging letter to Caddock for a sample might work?

Or, do the big mailorder companies ship to Australia (the parts are in
the few bucks range.. postage and shipping could be more)


Suzy,

I had a look at Farnell (au) for these type of resistors recently
(Caddock are not the only maker).

My recollection is that a 100W resistor is likely to be good for 50W -
60W in a practical application, and they were about $28 ea + $12
shipping, and IIRC minimum order quantity was one.

That is not to recommend them for a simple accurate load for 70cm.

Owen


But hopefully the Bird Termaline 50W model 8085 will do the job?




in AU, have you checked surplus places like
http://www.users.bigpond.com/alandevlin/forsale.html

Indeed, it shows a HP 774D as being sold, but perhaps he'd have other stuff.

"Suzy" not@valid wrote in :


But hopefully the Bird Termaline 50W model 8085 will do the job?

I think it is rated to 3GHz, look after it and it will be very useful.

People tend to overlook the value of a known dummy load, it is a very
useful piece of test equipment, and one of the first you should own.

If it is used, take the opportunity to test it some time.

With that in you kit, you have a chance of calibrating a VSWR meter
sampler.

You might find the following article of interest, skip the maths if it
gives you a headache, but the discussion towards the end is relevant to
setting up / testing a VSWR meter: http://www.vk1od.net/VSWR/VSWRMeter.htm
..

Perhaps you have some trusted ham neighbours who can help you out.

Owen

On Jan 31, 1:46 pm, Cecil Moore wrote:
K7ITM wrote:
See earlier posting in this thread.

Thanks Tom, when I said "linear power scale", I meant
e.g. a meter reading where 2000 watts is full scale
and 1000 watts is half scale. I have seen such meters
but not without a digital or analog computer on the
front end.
--
73, Cecil http://www.w5dxp.com

Right, and I'm saying that with a coupler or sampler that picks off,
say, 1e-7 of the power (0.2 milliwatts of RF out for 2000 watts in/
through), a diode detector that shows that power to be full scale on a
linear meter will show 1000 watts at half scale. That assumes that
0.2 milliwatts is low enough to get you into the square law region of
the detector; for an HSMS-2850 diode, that's a bit high. Because the
power at which the square law holds accurately is so low (and the
detector output is so low) you need an electronic way to read that
output; a simple meter movement isn't likely to do the trick. But
there's no need for any fancy processing.