MICRO MATCH / JONES 263 Power meter

[W4RFM]

I have a nice old MICRO MATCH made by Jones, a Model 263 that I am restoring.  The 3- 2.5 mH RF chokes were burned up, but the resistors looked okay.  They measure 23.9 ohms on the input or output connector.  I checked the BAMA online manual, and I cant find where it specifies the resistance of R1 on the coupler assembly.  Does anyone happen to know, or do you have a unit you could check that resistance/impedance for me?  Thanks

[Pete, WA2CWA]

I have a nice old MICRO MATCH made by Jones, a Model 263 that I am restoring.  The 3- 2.5 mH RF chokes were burned up, but the resistors looked okay.  They measure 23.9 ohms on the input or output connector.  I checked the BAMA online manual, and I cant find where it specifies the resistance of R1 on the coupler assembly.  Does anyone happen to know, or do you have a unit you could check that resistance/impedance for me?  Thanks

I'm confused. The coupler unit schematic shows R1 (in the Z1 Coupler Assembly) connected between the input and output connectors. Is R1 made up of multiple parallel resistors? If the schematic is correct, a resistance reading can be measured between input and output connector.

[k4kyv]

If that's the same device as the Micromatch that appeared in the 1947 QSTs, that measures SWR of balanced lines from 70 to 300 ohms, the resistor is 1 ohm, formed by ten 10Ω resistors mounted in a ring, with one of the balanced line connectors passing through it.  A revised circuit was described a couple of months later, with only nine resistors in parallel, to make the resistor 1.1 ohms.

I have been thinking of building one, but revising the circuit so that it will measure in the range of 450 ohms, and down to 1.8 mc/s.  The original circuit was designed for 80 through 10m, up to 300 ohms.  I believe I could make one work at least on 160-40m up to 450 ohms.

I few weeks ago I found one in my junk box.  Don't know where it came from, but it was missing a meter.  I stuck a 0-1 ma meter in it, but it still doesn't work.  Next thing will be to try replacing the diode. If I can get it to work, I plan to try modifying it to see if I can make it work in the frequency and impedance range I want.

It seems after those 1947 articles appeared, everything published since then has been for 50-ohm unbalanced, which is useless for what I want to use it for.

[WA1LGQ]

Bob, I just checked mine and R1 in the coupler consists of 16 10 ohm resistors in parallel making 1.6 ohms total which is what I measured from connector to connector. From connector to ground it was 40 or 41.6 depending on which connector was measured against ground. For the record it is marked model 263.3

........Larry

[k4kyv]

I just checked mine and R1 in the coupler consists of 16 10 ohm resistors in parallel making 1.6 ohms total which is what I measured from connector to connector.

16 ten-ohm resistors in parallel should measure 0.625 ohms.  If you are measuring 1.6 ohms, the composition resistors have increased in resistance with age, something I have observed with practically every carbon composition in my collection, whether new/unused or inside existing equipment.  Or else some of the paralleled resistors have opened completely.

[WA1LGQ]

Jeez, good catch Don. Its the simple things that I screw up. Thanks.........