Can anyone point me to a website where a home built 70 cm reflectometer or
70 cm field strength meter can be built -- not using surface mount
components. Thanks.

On Jan 28, 1:52 pm, "Suzy" not@valid wrote:
Can anyone point me to a website where a home built 70 cm reflectometer or
70 cm field strength meter can be built -- not using surface mount
components. Thanks.

Are you willing to use a printed circuit board? If so, a directional
coupler is pretty easy to make, microstrip style. You can even use a
knife to score the copper and then peel away the unwanted copper.
It's common to have one through-line and two coupled lines, one for
"forward" and one for "reverse" measurements. You terminate each
coupled line with Z0 (50 ohms, commonly) at one end and put a diode
rectifier (or other power measuring device) at the other end.
Although it's probably easiest to get a pretty good 50 ohm termination
at 450MHz using surface mount parts, you can do OK with a couple 1/4
watt metal-film axial resistors. If you used 1206 size surface mount
resistors, you should be able to solder them down with a decent
standard iron -- they aren't all that small.

If you really can't find any construction articles on making one,
maybe I could put something together and post it somewhere. They're
far easier to make than many people seem to think.

Cheers,
Tom

K7ITM wrote:
On Jan 28, 1:52 pm, "Suzy" not@valid wrote:
Can anyone point me to a website where a home built 70 cm reflectometer or
70 cm field strength meter can be built -- not using surface mount
components. Thanks.

Are you willing to use a printed circuit board? If so, a directional
coupler is pretty easy to make, microstrip style. You can even use a
knife to score the copper and then peel away the unwanted copper.
It's common to have one through-line and two coupled lines, one for
"forward" and one for "reverse" measurements. You terminate each
coupled line with Z0 (50 ohms, commonly) at one end and put a diode
rectifier (or other power measuring device) at the other end.
Although it's probably easiest to get a pretty good 50 ohm termination
at 450MHz using surface mount parts, you can do OK with a couple 1/4
watt metal-film axial resistors. If you used 1206 size surface mount
resistors, you should be able to solder them down with a decent
standard iron -- they aren't all that small.

If you really can't find any construction articles on making one,
maybe I could put something together and post it somewhere. They're
far easier to make than many people seem to think.

Cheers,
Tom

Don't let the surface mount parts intimidate you. Its not that
difficult especially when you are doing just a few componets. I must
admit that I had a heck of a headache after building a little
microphone preamp. I glue the part I am going to install to a
toothpick to give me something to hold it with.

Jimmie

"K7ITM" wrote in message
...
On Jan 28, 1:52 pm, "Suzy" not@valid wrote:
Can anyone point me to a website where a home built 70 cm reflectometer
or
70 cm field strength meter can be built -- not using surface mount
components. Thanks.

Are you willing to use a printed circuit board? If so, a directional
coupler is pretty easy to make, microstrip style. You can even use a
knife to score the copper and then peel away the unwanted copper.
It's common to have one through-line and two coupled lines, one for
"forward" and one for "reverse" measurements. You terminate each
coupled line with Z0 (50 ohms, commonly) at one end and put a diode
rectifier (or other power measuring device) at the other end.
Although it's probably easiest to get a pretty good 50 ohm termination
at 450MHz using surface mount parts, you can do OK with a couple 1/4
watt metal-film axial resistors. If you used 1206 size surface mount
resistors, you should be able to solder them down with a decent
standard iron -- they aren't all that small.

If you really can't find any construction articles on making one,
maybe I could put something together and post it somewhere. They're
far easier to make than many people seem to think.

Cheers,
Tom

Thanks very much Tom. Yes I'm certainly OK with PCBs and I was aware of the
basic circuitry. But I felt that the stripline would have to be special in
some way for the 435 MHz that I need. Perhaps a special length?

"Suzy" not@valid wrote in message ...
Can anyone point me to a website where a home built 70 cm reflectometer or
70 cm field strength meter can be built -- not using surface mount
components. Thanks.


How about an SWR meter with no surface mount components? See:

http://www.qsl.net/xq2fod/Electron/swr/swr.html

Have fun!

John

"John KD5YI" wrote in message
news:jFOnj.10273$fs4.5137@trnddc02...
"Suzy" not@valid wrote in message ...
Can anyone point me to a website where a home built 70 cm reflectometer
or 70 cm field strength meter can be built -- not using surface mount
components. Thanks.


How about an SWR meter with no surface mount components? See:

http://www.qsl.net/xq2fod/Electron/swr/swr.html

Have fun!

John
Thanks for that. I really want to emulate a throughline (like the Bird 43 I
once had) and am thinking more in the terms of a stripline on PCB (using
BNC), with parallel lines to sniff the RF and diodes to convert for the
meters. But what I'm usure of is the sort of dimensions I should use for 70
cms, and wther these are critical. How long should the stripline be, what
spacing and so on, so that it doesn't in itself introduce errors and
misleading results. The sort of thing I would imagine would be in the ARRL
handbook, but I want to avoid the expense of buying the book if it's not in
there at all. BTW, most of the designs I've seen are HF or for up to 2
meters at the highest. I specifically want 70 cms, 435 MHz to be exact.

Suzy wrote:
I specifically want 70 cms, 435 MHz to be exact.

I have a Micronta SWR/POWER METER speced for 440 MHz.
I suspect it uses a small ferrite core rated for 440 MHz
for the current pickup and a capacitive divider for
voltage. Seems all you need is a ferrite core rated
up to 440 MHz and you would be in business. Seems to
me that even a ferrite core not rated for 440 MHz
could be used and calibrated on a one to one basis.
--
73, Cecil http://www.w5dxp.com

On Jan 29, 10:23 am, "Suzy" not@valid wrote:
"K7ITM" wrote in message

...



On Jan 28, 1:52 pm, "Suzy" not@valid wrote:
Can anyone point me to a website where a home built 70 cm reflectometer
or
70 cm field strength meter can be built -- not using surface mount
components. Thanks.

Are you willing to use a printed circuit board? If so, a directional
coupler is pretty easy to make, microstrip style. You can even use a
knife to score the copper and then peel away the unwanted copper.
It's common to have one through-line and two coupled lines, one for
"forward" and one for "reverse" measurements. You terminate each
coupled line with Z0 (50 ohms, commonly) at one end and put a diode
rectifier (or other power measuring device) at the other end.
Although it's probably easiest to get a pretty good 50 ohm termination
at 450MHz using surface mount parts, you can do OK with a couple 1/4
watt metal-film axial resistors. If you used 1206 size surface mount
resistors, you should be able to solder them down with a decent
standard iron -- they aren't all that small.

If you really can't find any construction articles on making one,
maybe I could put something together and post it somewhere. They're
far easier to make than many people seem to think.

Cheers,
Tom

Thanks very much Tom. Yes I'm certainly OK with PCBs and I was aware of the
basic circuitry. But I felt that the stripline would have to be special in
some way for the 435 MHz that I need. Perhaps a special length?

The stripline (microstrip, really, if it's on one side with
groundplane on the other, which is the easiest to do) can be almost
any length. It will have zero coupling if it's an electrical halfwave
or integral multiple of a halfwave, but otherwise, it will work. It
will have the maximum coupling if it's an electrical quarter wave
long, and the change in coupling versus frequency is minimum at that
length, but it's usable even if it is very short. I'm using one
that's about half an inch long down as low as 1MHz; the directionality
is fine, and the coupling is simply very small. You can use the free-
to-download RFSim99 program to get a microstrip design for a
particular coupling, but what the program doesn't tell you is that the
coupling they list is for a coupler an electrical quarter wave long.
To a pretty close approximation, the coupling will go as the sine of
the electrical length, so for example if you use the design for a 20dB
coupler but make it only 1/8 wave long, the response will be about
sin(45 degrees) or .707 times as much, or 3dB lower: it will be about
a 23dB coupler at that length. That means the coupled port power will
be 23dB lower than the input power, so if you had 10 watts going in,
the coupled port would receive about 0.05 watts, which is 1.6V rms.
That likely is a bit more than you need to drive a diode detector.
There can be some advantage to keeping the voltage low enough, if
you're using a diode detector, so that the detector is in the "square
law" region: DC output _voltage_ is proportional to RF input
_power_. On normal FR4 board stock 1/16" thick, leaving one side as a
ground plane, a pair of traces 1/8" wide, separated by a 1/8" space,
will give you about a 25dB coupler and pretty close to 50 ohms. It
does depend on the particular dielectric constant of your FR4
substrate, which varies from manufacturer to manufacturer and by
particular material type. In that microstrip environment, the
wavelength of 450MHz signals will be on the order of 40cm, or about 4
inches for 1/4 wavelength, so you can see that your coupler doesn't
have to be very long, physically.

If you don't mind working with SMA connectors, you can get SMA jacks
that mount directly on the edge of a 1/16" thick PC board, and that
makes it very easy to make a connectorized version of a coupler. You
can get SMA-to-BNC (or to other series) adapters--mpja.com have them
at reasonable prices, for example--to get to other environments.

If I wanted a coupler for a power/SWR meter for 450MHz, and assuming I
was going to use Schottky diode detectors, I'd first think about the
range of powers I wanted to handle, then select a coupling to give me
perhaps 0.2V RMS at max power at the coupled port. If space
permitted, I'd make the coupler an electrical quarter wave long, since
its sensitivity would then be least affected by frequency (the very
flat top of the sine curve). I'd use a DVM to read out the detected
DC voltage (and make sure my DVM or digital panel meter or whatever
wasn't affected by the 450MHz signal directly!). A 200mV full-scale
3.5 digit meter would then cover to very low SWR at full scale, and to
fairly low power. The one other thing I'd want to do is insure that
the meter--the directional coupler part, specifically--was optimized
to 50 ohms, which would require a known good 50 ohm (assuming I wanted
it to be 50 ohms) load to test. Likely I'd make some pretty accurate
measurements of the board substrate thickness and relative dielectric
constant before starting, so I got the trace widths and spacings right
from the start. It's possible to trim the coupler up in impedance by
carefully narrowing the traces, and down by adding a grounded plane
above the board--adjusting the spacing to trim the impedance. Be
aware that each of those will also change the coupling slightly,
however.

Hope that helps some!

Cheers,
Tom

"Suzy" not@valid wrote in :

....
Thanks for that. I really want to emulate a throughline (like the Bird
43 I once had) and am thinking more in the terms of a stripline on PCB
(using BNC), with parallel lines to sniff the RF and diodes to convert
for the meters. But what I'm usure of is the sort of dimensions I
should use for 70 cms, and wther these are critical. How long should

If you make the coupling line very short wrt wavelength, you can analyse
it with a lumped constant approximation.

You can think of the coupled line as located in the electric field of the
main line, and it will have a voltage difference to ground.

Similarly, the coupled line will be cut by magnetic flux due the the
current in the main line, and so a voltage will be induced end to end in
the coupled line.

By adjusting the resistor at one end of the coupled line, you adjust the
contibution of these current and voltage derived samples, and can adjust
them so balance each other (ie no meter deflection) when V/I on the main
line is 50.

When the coupled line is short, the characteristic impedance of the
coupled line is not very critical.

You should be able to achieve sufficient sensitivity for 5W pwr on 70cm
with 20mm of coupled line.

The Zo of the though line is more important, it is the main determinant
of the insertion VSWR of the instrument, so you need to strive to achieve
close to the desired Zo, presumably 50 ohms.

Next, don't put the coupled line to close as it will load the main line
and degrade the insertion VSWR.

Then adjust the R at the end of the coupled line to null the DC output on
a 50 ohm load.

Repeat for the other coupled line (if you use one).

Check for symmetry, ie that reversing the instrument gives exactly the
same readings on the dummy load.

Tom suggested Schottky diodes. Dick Smith has 1N5711 Shottky diodes (at
exhorbitant prices), or you could get 1N34 germainium diodes from Jaycar.

BTW, you did mention the Bird 43, the above is not frequency compensated
like the Bird slugs, deflection will be frequency dependent.

Owen

PS: I have only met one VK YL ham named Susan, I sometimes wonder what
happened to her, haven't heard her on air in decades.

On Jan 29, 6:01 pm, Owen Duffy wrote:
"Suzy" not@valid wrote :

...

Thanks for that. I really want to emulate a throughline (like the Bird
43 I once had) and am thinking more in the terms of a stripline on PCB
(using BNC), with parallel lines to sniff the RF and diodes to convert
for the meters. But what I'm usure of is the sort of dimensions I
should use for 70 cms, and wther these are critical. How long should

If you make the coupling line very short wrt wavelength, you can analyse
it with a lumped constant approximation.

You can think of the coupled line as located in the electric field of the
main line, and it will have a voltage difference to ground.

Similarly, the coupled line will be cut by magnetic flux due the the
current in the main line, and so a voltage will be induced end to end in
the coupled line.

By adjusting the resistor at one end of the coupled line, you adjust the
contibution of these current and voltage derived samples, and can adjust
them so balance each other (ie no meter deflection) when V/I on the main
line is 50.

When the coupled line is short, the characteristic impedance of the
coupled line is not very critical.

You should be able to achieve sufficient sensitivity for 5W pwr on 70cm
with 20mm of coupled line.

The Zo of the though line is more important, it is the main determinant
of the insertion VSWR of the instrument, so you need to strive to achieve
close to the desired Zo, presumably 50 ohms.

Next, don't put the coupled line to close as it will load the main line
and degrade the insertion VSWR.

Then adjust the R at the end of the coupled line to null the DC output on
a 50 ohm load.

Repeat for the other coupled line (if you use one).

Check for symmetry, ie that reversing the instrument gives exactly the
same readings on the dummy load.

Tom suggested Schottky diodes. Dick Smith has 1N5711 Shottky diodes (at
exhorbitant prices), or you could get 1N34 germainium diodes from Jaycar.

BTW, you did mention the Bird 43, the above is not frequency compensated
like the Bird slugs, deflection will be frequency dependent.

Owen

PS: I have only met one VK YL ham named Susan, I sometimes wonder what
happened to her, haven't heard her on air in decades.

Owen's comments reminded me that I always used to think of coupled-
line hybrids as sampling the magnetic and electric fields at a point,
and of course you can adjust the ratio by adjusting the load as he
suggests. But then something began nagging me: his example of a 20mm
(2cm) line isn't exactly short compared with a "full length" quarter
wave coupled line. Because of the relatively slow propagation in
stripline over FR4 PC board material, a quarter wave is only about 10
cm for 450MHz signals. But thinking of it in terms of a distributed
line system, you're just terminating the coupled line in the proper
impedance to not get reflections off that end; so this same thing
works even with full 1/4 wave lines to adjust the directivity.

However, if you have one through line and one coupled line, and you've
made them very symmetric so you can swap the two and not see a
difference, then if you have to terminate the coupled line in other
than 50 ohms to get perfect directivity (no reflection from that
port), it also says that the through line is not 50 ohms. As Owen
points out, you'd really like that through line to look like 50 ohms
(or other system Z0 if you wish), so it doesn't disturb the system
it's installed in. There's the incentive to make the coupler
symmetrical and tuned so the coupled line terminates properly in 50
ohms, to get best directivity.

I'll readily admit that the details of coupled lines from a fields
perspective is a bit beyond my full understanding, so there may be an
error in my thinking about this, but I believe it's pretty accurate.
The thing that comes first to my mind is that for stripline, the
propagation velocity for even and odd modes is different, but still, I
think if the lines are lightly coupled, the paragraphs I wrote above
are a valid way to look at the situation.

Geez, Schottky diodes should be dirt cheap these days. It's germanium
that are hard to find around here, unless they are old stock.

Cheers,
Tom