Devoted entirely to Amateur radio

Build your own LF/Audio instruments

m1. LC and Q-meters
m2. RF detectors, level meters, attenuators, dummy loads, signal dividers
m3. RF signal- and power generators
m11 Grid dip meters
m12 Power- and VSWR-meters
m21 Norwegian instruments
m22. Old measuring instruments
m23. Signal-to-noise-meter

1a) Audio/LF impedance measuring instrument. May also be used to find a figure for balance for a telephone line,
as so-called Balance-tester, and it may be set for an impedance and measure a figure of reflection loss on a line, but
the instrument should have level reading calibrated in dB/dBm.

1b) Balance-tester. Have used it at work to search for improper connections in analogue telephone exchanges, some wires
were grounded and caused bad crosstalk between subscriber lines, used 10kHz to avoid interference for the subscribers.
This simple application for 600 ohm balanced lines depends on the input/output transformers in the measuring equipment,
for the mentioned HP instruments it is no problem, and it may also work for Wandel&Goltermann SPM-3/PS-3 combination,
but the latter already have a bridge circuit implemented to measure mean impedances (real, but not imaginary values).

1c) Audio bridge construction using 30x45mm piece of single-sided PCB laminate, to be plugged
on to the instrument.
The pcb copper sectors are made using hacksaw.

1d) Test set-up for measuring an audio transformer's impedance. I must admit that the HP4934 or HP4936 digital audio
meters aren't the most practical to adjust for minimum deflection, used similar board earlier with a Siemens analogue
instrument (0.3-2.2MHz), but it is easy when you can mount the board on to a dual function RX+TX instrument.


2) LF/MF impedance measuring bridge. The advantage with this bridge is that it is not important to
calibrate the potmeter reading, you just use a VOM when everything is disconnected from
the coax connectors. Have used it to measure mixer termination impedance using sufficient
low RF drive.
This is the same bridge as mentioned above, but has an extra transformer to balance the signal
for receiver connection. All connections are done with coax connectors, in this case the high quality
gold plated conhex type (75 ohm) which is available free in larger quantities from radio link equipment,
but BNC or phono types could be used if you prefer another standard type.

C.98 Diverse komponenter for amatørradioformål (components for amateur radio purposes)