On Sun, 22 Feb 2004 13:35:55 -0000, "owen.home"
wrote:
I have two of these units both measure 50 ohms.
Also found the manual for it. It will be a while before I could copy
it for you.

Hello
I recently went to buy an RF sweep generator and ended up bringing home a
TS-118A/AP (Bird) RF wattmeter, as one does! I have some questions:-
1. Given that the RF power sensors for the various bands/power ratings are
added external to the meter with only the coax connecting through to the
unit,how does it work? I assume the sensors are thermocouple types but
there's no separate DC circuit and I can only see a narrow constriction in
the sensor with the centre core being a very fine wire.
2. I'm missing the calibration/multiplication factor graph for the MX-1784/U
sensor, would anyone have one they'd be prepared to scan and email for me?
Any pointers to a full manual on the net would be good also.

The MX-1784 is a tuning shunt used for safety reasons
on transmitters with capacitively coupled outputs.
3. Although the unit is marked 20-1400MHz at 500W, the MX-1783/U graph shows
power levels up to 1200W at 40MHz, I guess the unit is very conservatively
rated but does anyone have true figures (not that I intend to work at that
sort of power levels).
The manual speced power levels are.

Range 20- 1400mhz
power 20-100mhz 2-300watts
100-300mhz 2-500watts
300-750mhz 2-125watts
750-1400mhz 2-125 watts
4. Is it OK to use as a straight dummy load without the sensor, I've tested
it at 2m and it seems fine but why the 20MHz lower limit? also it doesn't
measure 50 ohms at DC so I guess it can't be a straight resistor so what's
the load?
The lower 20 mhz limit is to prevent damage to the metering circuits.
It can be used to DC if you disconnect the metering circuit.
I learned the hard way!!!!!

It is a straight 50 ohm resistor in the oil. If you measure anything
much differnet the resistor is defective.

I'd appreciate all and any information you can give about the wattmeter,
it's not something I'd have planned on buying but it looks like it'll serve
all the needs I'd ever have for a high power dummy load/wattmeter other than
for the lower HF bands.
Thanks in advance
John