The AM Forum

Probably a simple thing to do, but I would appreciate as much info as I can get.

I have come across a stack of ILS modulators, rated to do 90 hz and 140hz.

They appear to be fairly standard plate and screen type of mod.

The original layout used a pair of 807s at output bottles.

Sadly I have no other info.

I want to test the frequency response, impedance ratio, and make an educated guess at power handling (currently thinking they will be good for 100W of audio.

Any pointers?

Sean

post a picture?

When you say "plate and screen" what are you referring to?

Not familiar with "ILS".

Pair of 807s are more like 60watts or less, unless they were run with very high B+ and in AB2, then maybe 100 watts.

                _-_-bear

Yes , ICAS pp pair at 750 volts Ep, 108 watts output.
A great tube.

ILS =  "Instrument landing System"  consists of an am localizer transmitter for angular horizontal guidance at about 114 MHz, a Glideslope transmitter at about 328 MHz for angular vertical guidance, and two or three "marker beacon" 75 MHz transmitters indicating positional passage.

The entire system is the highest performance means by which all aircraft operating under Instrument Flight Rules set up on final approach to enable them to transition to visual landing - at 200 or 100 feet above the threshold, or, in the case of the highest performance autopilots, auto-touchdown.

It's really something to take off visually, enter clouds at 500 feet, fly the gauges for two hours, seeing nothing but your instrument panel in front of your eyes, set up on the ILS, and at 200 feet agl look up to see the leading runway strobes, and touching down ten seconds later.

Usually you can get on top of the clouds for most of the flight, but when the wx is really stinky, it gets sporting.

Chris

Is it not 150Hz? Not to nitpick but I have a 90 & 150 Hz rotary tone generator with Bendix wings on it.

I have three of the units - two at 140hz, one at 90hz.

Will pop a piccy up, but it is just a big black cube about 18lbs in weight, centre tapped primaries, and single output with electrostatic screen.

Perhaps it will just be a case of rigging something up and seeing what happens.

Sean

You can put a small voltage on the primary side, read the output of the secondary side and calculate the turns ratio....There is a thread on this forum about testing unknown mod transformers for spec...

Testing the freq response will likely require driving the 807s and seeing what the response looks like into a suitable resistive load. First I'd want to do the suggested test to determine the turns ratio.

Given that the requirement was to make single tones at relatively low freq, they may have opted to use rather "poor" transformers, even power transformers that do not have particularly good higher frequency response...

                    _-_-bear