70cm reflectometer?
 

"K7ITM" wrote in message
...
On Jan 31, 5:01 pm, Jim Lux wrote:
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.

:-) I've thought maybe I could just etch one next time I'm making
boards and drop it in the mail to her. Heck, I'd even toss detector
diodes and terminating resistors on it.

Cheers,
Tom

Thanks Tom, but give me a practical design! I can do the board if you give
me the dimensions.

70cm reflectometer?
 

"K7ITM" wrote in message
...
On Jan 31, 3:19 pm, "Suzy" not@valid wrote:


"K7ITM" wrote in message
...
See earlier posting in this thread. See various Avago ap notes, such
...


Much too theoretical for me!

OK, here's non-theoretical, practical.

Get a piece of FR4 PC board material, copper-clad both sides, 50mm
wide by 110mm long (neither of these is very critical, but should be
at least that long) by 1.6 mm thick. One side will remain all copper
clad, as a ground plane. On the other side, fabricate at a minimum
three traces, as follows. To make it easier to describe, assume you
are looking at the board with the 110mm dimension horizontal and the
50mm dimension vertical.
Trace 1: the through-line. It will run the length of the board
(110mm), centered between the two sides. It will be as close as you
can make it to 2.9mm wide, uniform width from board edge to board
edge.
Trace 2: It will also be as close as you can make it to 2.9mm wide
for its whole length. The following is the center-line of the trace.
Start at the top edge of the board, 9mm from the left side. Go down
to 9.0mm above the center-line of the through-line trace (Trace 1).
Turn toward the right edge of the board and follow parallel to trace
1, staying 9.0mm center-to-center. Thus there should be a gap of
6.1mm between the two traces. Go a distance of 92mm. Turn toward the
top of the board, and extend the trace all the way to the top.
Trace 3: It will be the mirror-image of trace 2, same 2.9mm width.
It will start 9mm from the left side at the BOTTOM edge, go up till
its centerline is 9.0mm from trace 1, follow trace 1 to the right for
92mm, and then return to the bottom edge of the board.

Mount an edge-mount BNC connector to each end of trace 1, shell to the
ground plane and center pin to the trace. Failing that, do something
equivalent with coax or connectors...if you trimmed the end of a piece
of coax so the braid connected to the back side of the board and a
very tiny stub of exposed center conductor could be soldered to the
end of trace 1, that should be OK.

You'll need two 50 ohm load resistors. 1/4 watt is plenty. Since 50
ohms is not a common value, you may wish to use two 100 ohm resistors
in parallel for each of these 50 ohm guys. Solder one of them so it
connects with vanishingly short leads between the RIGHT end of trace 2
(at the top of the board) to the back-side copper immediately opposite
that point. The resistor(s) will be soldered to points immediately
opposite each other, front and back side. Solder the other 50 ohm
resistor between the LEFT end of trace 3 (at the bottom edge of the
board) and the back side of the board. Those are the termination
resistors, and they are the ones you would adjust to get the best null
when feeding power through trace 1 to a good 50 ohm termination.

Now you'll need two detector diodes (maybe Owen can help out here; I'd
use some surface mount schottkys, but...) and two small ceramic
capacitors. 100pF would be a good value, but it's not critical. All
leads should be so short you have trouble seeing that there's any lead
there at all. Solder one lead of a capacitor to the LEFT end of trace
2 (at the top of the board), and one lead of the other capacitor to
the RIGHT end of trace 3 (at the bottom of the board). Those are the
ends without resistors. On the back of the board immediately behind
where you soldered the capacitors, solder the ANODE of a diode, one
for trace 2 and one for trace 3. Arrange things so that the free lead
of the capacitor and the free lead of the diode (the cathode) come
together off the edge of the board. OK, I lied: leave enough lead to
solder another part to, there.

Now get or make a couple small RF chokes, about 100 nanohenries. The
inductance isn't critical. The way I'd do it is to wind some magnet
wire onto a small machine screw. For example, try about ten turns on
a 4mm screw. The wire diameter should be roughly 1/2 to 3/4 the screw
thread pitch. You can then unscrew the screw and if you're careful
with it, the inductor will be reasonably self-supporting. Next,
you'll install these two and a couple more capacitors. Small ceramic
capacitors, say something in the range from 100pF to 1000pF, should do
nicely. With the board turned over so the back is now facing you,
solder one side of a capacitor just a bit in-board from where you
soldered the diode anode for trace 2. Do the same for trace 3. Now
connect an RF choke (inductor) between the diode-capacitor junction
and the free lead of the new capacitor.

You can make things a bit more robust if you mount some sort of
terminal or pad on the back to solder this last junction to. One very
cheap but effective way to do it is to cut out some squares of PC
board material, maybe 5mm on a side, and glue them down to the large
board wherever you want an electrically floating terminal.

Just about done now! Just connect a wire from each of those last
capacitors (where wired to the inductors of course) to the + terminals
of the two 1.0mA meters, and return the meter - terminals to the board
back sides. Provide a case as you see fit, though it's usable without
a case; just be careful of the parts hanging off it.

After you build it, we can lead you through calibrating it, assuming
the earlier descriptions here weren't clear enough.

And I trust several lurkers will proof-read this and find all my
mistakes and places where I wrote LEFT when I meant RIGHT, etc. Oh,
and the meter connected to trace 2 will measure the power from left to
right in the original orientation; and the meter connected to trace 3
w2ill measure power from right to left.

Cheers,
Tom

At last! And with my new Bird dummy load nearly here I should be away at
last!

70cm reflectometer?
 

Ian White GM3SEK wrote in
:

Owen Duffy wrote:
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).


Do Australian TVs use "Bloody Belling Lee" connectors like we still do
in the UK? What does "PAL" stand for?

Yes, the TVs invariably have the Belling Lee connector, now known as the
PAL connector. I don't know how it got the PAL label, perhaps related to
its use in the UK where PAL colour encoding was used (as it is here in
Oz). Apparently the PAL connector was invented in 1922 and complies with
BS and IEC standards.

I did some tests on BL connectors in the seventies and performance up to
2GHz was better than UHF connectors, and quite acceptable. The BL
connectors that I tested were plated brass bodied male connectors with
soldered centre pin, and plated steel bodied female connectors (all in
good condition).

Modern practice is to install F connectors in fixed wiring. There is a
range of quality in F connectors, but the Gilbert style connectors seem
reliable so long as they are done up tight with a spanner. A 'feature' of
F connectors that might mitigate against widespread adoption on
appliances.

On a related subject, the so called 'compression type' F connectors seem
to properly terminate RG6, and are available in BNC. They are a ready and
inexpensive source of weatherproof BNC termination of RG6. (Some pics at
http://www.vk1od.net/RG6/index.htm .)

Owen

70cm reflectometer?
 

Owen Duffy wrote:
Do Australian TVs use "Bloody Belling Lee" connectors like we still do
in the UK? What does "PAL" stand for?

Yes, the TVs invariably have the Belling Lee connector, now known as
the PAL connector. I don't know how it got the PAL label, perhaps
related to its use in the UK where PAL colour encoding was used (as it
is here in Oz).

OK, that makes sense.

[ Incidentally, for anyone who hasn't seen the 'alternative' meanings
for the various international color TV standards:

NTSC (USA) = Never Twice the Same Color
SECAM (France) = Something Else, Contrary to American Methods
PAL (rest of western Europe, Australia and NZ) = Perfection At Last. ]


Apparently the PAL connector was invented in 1922 and complies with BS
and IEC standards.

Or rather, the standards had to comply with the connectors, because the
connectors were there first.

I did some tests on BL connectors in the seventies and performance up
to 2GHz was better than UHF connectors, and quite acceptable. The BL
connectors that I tested were plated brass bodied male connectors with
soldered centre pin, and plated steel bodied female connectors (all in
good condition).

That's fine... now try again with the much more common aluminium bodied
plug, and a centre conductor wire that was pushed into the centre pin 20
years ago, was never soldered and is now heavily tarnished.

That unsoldered 'maybe-connection' inside the centre pin is a major
cause of poor reception and TVI in the UK... along with water in the
coax, which has an interesting effect when the water reaches the
aluminium/copper connection inside the plug body. The whole thing is a
classic example of insane design.

Modern practice is to install F connectors in fixed wiring.

Much better, as those are specifically designed to be solderless.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

70cm reflectometer?
 

Ralph Mowery wrote:

"Cecil Moore" wrote in message
t...
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

Just jumping in the middle of ths, but look at this watt meter.

http://bama.edebris.com/manuals/miltest/an-urm120/

It has a linear scale. I have one and it has a linear scale. Sort of made
like a Bird meter but much larger elements. It is just a diode and meter.
There is no power needed to run the meter except the sampled power comming
off the transmission line.

There were several versions made. One has a SWR scale on it. I am not sure
how the swr scale is but the wattmeter scale is linear instead of the log
looking scale of the Bird and most other meters.

To have a linear power calibration, that has to be a square-law
detector. On the higher-power ranges, the slug is moved away from the
centre conductor, so that the diode is always operating within its
accurate square-law range.

Thanks very much for posting that link, Ralph. It's interesting to see
the resemblances to the Bird 43, and also the differences.

The Bird meter scale is not logarithmic. It's better described as being
in the transition region between a square-law detector at low meter
currents, and a voltage-detecting rectifier towards the high end of the
meter scale. The compression in the upper half of the power scale is
because the diode is acting as a voltage detector. Power is proportional
to V-squared, so the meter deflection is tending towards the square root
of the power, and that is what compresses the scale towards the high
end.

As with the AN-URM120, the Bird design adjusts the coupling so that all
detector diodes in all the inserts are operating at the same RF levels,
so they can all share the same meter scales. The difference is that
instead of physically moving the same insert inward or outward to adjust
the coupling, Bird do it by selling us more slugs :-)


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

70cm reflectometer?
 

On Sat, 2 Feb 2008 08:45:27 +0000, Ian White GM3SEK
wrote:

As with the AN-URM120, the Bird design adjusts the coupling so that all
detector diodes in all the inserts are operating at the same RF levels,
so they can all share the same meter scales. The difference is that
instead of physically moving the same insert inward or outward to adjust
the coupling, Bird do it by selling us more slugs :-)

Hi All (Congratulations Ralph),

There are more differences than that. The Bird suffers more from
parts erosion than the URM120 as the URM has bigger elements. With
the bigger elements, the geometries are held to a tighter precision.

It is the coupling link that moves in the URM, not the element. The
link rides on a cam that is stepped for the 4 different power ranges
used. If you remove the knob from the slug, and then the cover plate,
you have access to an adjustment screw that provides the fine control
over the depth of penetration. The smaller PDF at the boat anchors
web page is the more useful of the two offered.

I have calibrated a pile of both the Birds and the URMs, and the URMs
always required less maintenance, and rarely needed adjustment. The
Birds, on the other hand, always arrived out of calibration.

One source of error in the VHF/UHF region was that the rubber gasket
inside the N connector (and for that matter, for any N connector) will
accumulate thread debris. It should be used as a visual correlative
to the amount of similar debris bridging the Teflon insulator. This
debris can whack out these meters and degrade connections.

73's
Richard Clark, KB7QHC

70cm reflectometer?
 

"Richard Clark" wrote in message
...
On Sat, 2 Feb 2008 08:45:27 +0000, Ian White GM3SEK
wrote:

As with the AN-URM120, the Bird design adjusts the coupling so that all
detector diodes in all the inserts are operating at the same RF levels,
so they can all share the same meter scales. The difference is that
instead of physically moving the same insert inward or outward to adjust
the coupling, Bird do it by selling us more slugs :-)

Hi All (Congratulations Ralph),

There are more differences than that. The Bird suffers more from
parts erosion than the URM120 as the URM has bigger elements. With
the bigger elements, the geometries are held to a tighter precision.


I was luckey enough to find one that was in the origional wrapping paper. I
don't remember what the date was on the wrapper. At a hamfest several years
ago soneone had several new ones. They were in the heavy duty aluminimum
foil , cardboard box, and the hard plastic foam filled case. Never opened
from the day they were calibrated about 10 or 20 years before. It came
with 3 elements that would go from about 3 mhz to 1000 mhz. Think it topped
out at 1 kw up to 30 mhz and 500 watts after that. I bought it for what
some used Birds without elements seem to go for on e-bay now.
One minor thing is the meter movement on those meters are sluggish so it
takes a slow adjustment of amplifiers to get them to the max output.

70cm reflectometer?
 

On Sat, 2 Feb 2008 12:10:10 -0500, "Ralph Mowery"
wrote:

One minor thing is the meter movement on those meters are sluggish so it
takes a slow adjustment of amplifiers to get them to the max output.

Hi Ralph,

The meter needle probably has an aluminum vane in the magnetic field
that is used as a dampener through eddy current induction.

As a general consideration for fine meter movements, and to prevent
their being damaged while being transported; some are equipped with
shorting bars (or switches) across the meter terminals. This is more
commonly encountered with bridge instruments.

This can be simple observed by rotating the meter movement quickly and
noting the deflection of the needle on the scale through inertia. An
undampened meter can be deflected by vigorous movement up to half
scale (possibly more), where a dampened meter would deflect barely a
tenth.

You got a bargain beyond dollars in your purchase.

73's
Richard Clark, KB7QHC

70cm reflectometer?
 

On Feb 2, 9:10 am, "Ralph Mowery" wrote:
"Richard Clark" wrote in message

...

On Sat, 2 Feb 2008 08:45:27 +0000, Ian White GM3SEK
wrote:

As with the AN-URM120, the Bird design adjusts the coupling so that all
detector diodes in all the inserts are operating at the same RF levels,
so they can all share the same meter scales. The difference is that
instead of physically moving the same insert inward or outward to adjust
the coupling, Bird do it by selling us more slugs :-)

Hi All (Congratulations Ralph),

There are more differences than that. The Bird suffers more from
parts erosion than the URM120 as the URM has bigger elements. With
the bigger elements, the geometries are held to a tighter precision.

I was luckey enough to find one that was in the origional wrapping paper. I
don't remember what the date was on the wrapper. At a hamfest several years
ago soneone had several new ones. They were in the heavy duty aluminimum
foil , cardboard box, and the hard plastic foam filled case. Never opened
from the day they were calibrated about 10 or 20 years before. It came
with 3 elements that would go from about 3 mhz to 1000 mhz. Think it topped
out at 1 kw up to 30 mhz and 500 watts after that. I bought it for what
some used Birds without elements seem to go for on e-bay now.
One minor thing is the meter movement on those meters are sluggish so it
takes a slow adjustment of amplifiers to get them to the max output.

I have one of those, or something very similar; a Struthers 1219-D.
The HF slug that came with mine goes up to 5kW, though. The meter
movement measures 24uA full scale, and the coil resistance is 2k ohms,
so the meter is pretty sensitive: about 1.1 microwatts for full scale
deflection. It takes that sort of sensitivity to get down to the
linear detector out versus RF power in region.

Interestingly, if I simulate a single-diode detector using an
HSMS-2850 Schottky diode into a 2000 ohm load, and find the RF voltage
that gives 24uA output, and then re-simulate with voltages in the
right ratios to give 90% of that power, 80%, 70%, etc., down to 10%,
the outputs are not exactly linear with input power. The error is
small, though, no more than about 1.5% of full scale. So then I
checked the calibration on my meter, and put in 50% of full scale
current, and noted that the meter reading is not exactly 50, but just
enough off to be correctly reading the RF power. So though the scale
on my meter appears at first glance to be linear, it's not exactly so,
and I believe that must be intentional. The worst-case "error" to
linear output in the simulation was at 70% of full power, where the
current is predicted to be 71.43 percent of full scale. On my meter,
when I put in 71.43% of full scale, indeed it reads almost dead-on 70%
power. I doubt that's a fluke.

Cheers,
Tom

70cm reflectometer?
 

"Richard Clark" wrote in message
...
On Sat, 2 Feb 2008 12:10:10 -0500, "Ralph Mowery"
wrote:

One minor thing is the meter movement on those meters are sluggish so it
takes a slow adjustment of amplifiers to get them to the max output.

Hi Ralph,

The meter needle probably has an aluminum vane in the magnetic field
that is used as a dampener through eddy current induction.

As a general consideration for fine meter movements, and to prevent
their being damaged while being transported; some are equipped with
shorting bars (or switches) across the meter terminals. This is more
commonly encountered with bridge instruments.

This can be simple observed by rotating the meter movement quickly and
noting the deflection of the needle on the scale through inertia. An
undampened meter can be deflected by vigorous movement up to half
scale (possibly more), where a dampened meter would deflect barely a
tenth.

You got a bargain beyond dollars in your purchase.

73's
Richard Clark, KB7QHC

Yes, I did get a great bargain. The meter came with a spring type wire
across the meter to short it out. I know this helps protect the meter
movement. Just have to remember to take it out when I want to use the
meter. Some of the old analog VOMs had an off position that did the same
thing.

Some of the Bird Hammate wattmeters had the very slow movements and Bird
would change them out for you.