John Henderson N4NAB wrote:
Need some advice on test gear, signal source, swr measurement for L and S band. Just got 1.2 board for 910H and have unit on order for 2.4 from SSB. Home brewing antennas and need some way to check/adjust. My MFJ is only good for up thru 70cm.
You might want to consider some surplus HP equipment.
The HP432a power meter will cover any frequency you are likely to need. It requires the additional purchase of a thermistor head. The 478A head is good to 11 GHz, and 8478B head is good from 10 MHz to 18 GHz. You also need the thermistor cable.
This setup covers a power range of 10 microwatts to 10 milliwatts full scale. So you would also want a few precision attenuators so that you can measure power levels higher than 10 mW without destroying the thermistor head. A -30dB, 10 watt attenuator would bring a 10 watt signal down to 10 mW, or full-scale at the maximum power range of this gear. I also found a -40dB, 50 watt attenuator that brings 50 watts down to 5 mW or half the power rating of the thermistor. If you were brave (or foolish) you could put 100 watts through this attenuator very briefly and the thermistor would be happy at 10 mW maximum. But precision attenuators don't retain their precision qualities if overheated with excessive power, so go easy there.
Now, this still doesn't get you the ability to measure SWR, or measure forward and reflected power into/out of an antenna. To do that, you need one more piece, which is a directional coupler. Power goes into the directional coupler and its output is connected to the antenna or other device under test (DUT). You connect your power meter's thermistor to the forward or reflected coupling port. By measuring forward and reflected power, you can determine the SWR.
Sure, the Bird 43 wattmeter is convenient -- power in one side, antenna connects to the other side, and you can read the SWR right off the main dial. The "problem" with the Bird is that you have to buy additional "slugs" for every frequency band and every power level of interest. With the HP system described above, you only need one meter, one cable, and one thermistor to measure power at any frequency between 10 MHz and either 11 or 18 GHz. Although some precision attenuators are frequency specific, you can easily buy only attenuators rated to 18 GHz and you are good for any frequency that the meter can measure. Likewise, directional couplers have highest precision at specified ranges of frequencies, but in many cases, you can calibrate one with the above setup plus a good 50 ohm dummy load. By calibrate I mean that if the dummy load is near 1:1 SWR, the forward power coming out of the coupler at the frequency of interest can be easily measured with the dummy load on the output, and you now know what the coupling level of the forward port is, whether -10dB, -30dB, -16.2dB, or whatever it turns out to be. Then you physically rotate the device (put power into the output port, put the dummy load on the input port, and measure the forward power coming out of the "reverse" coupler port). Now, even though the coupler might not have been designed to work at 2400 MHz, if the coupling is measured in this way, the coupler is usable unless the coupling you measure is extremely poor.
That may be a bit more of an answer than you were looking for. But this setup seems to be much more versatile to me than a Bird 43 with a box full of slugs. I actually bought a couple of HP432a meters, thermistor cables, and 8478B thermistor heads, and 18 GHz attenuators of -10, -20, -30, and -40 dB, plus a two-way directional coupler. With these pieces, I can measure power from microwatt levels to tens of watt levels at any frequency for which I have equipment, as well as forward/reflected power and (indirectly) SWR. No, I don't have any 24 GHz equipment and this setup would not test it if I did, but you'll not find a 24 GHz slug for a Bird 43 either! On the other hand, it is possible to buy a K486A waveguide thermistor for the 432A and measure 18 to 26.5 GHz too!
If you're interested, the following HP/Agilent operator's manual for the 432A would be a good place to start reading: http://cp.literature.agilent.com/litweb/pdf/00432-90079.pdf
73 de WØJT AMSAT-NA LM#2292