Saturday, October 23, 2010

2304 MHz Transverter - Transmitter Construction

After what seemed like forever, the ABPM (All Band Power Meter) arrived from Down East Microwave.  I had also ordered 2 ERA-2 amplifier boards at the same time.  I had the power meter built that evening, and went to test it, and the microwave detector does not work.  The parts in that section are extremely tiny, and I'm thinking I popped the detector chip.  I think it was probably my fault.  I also believe I'm losing my touch, as I'm having more difficulty working with surface mount parts due to their size.  I think I need to invest in one of those big magnifyers with the light in the head if I plan on continuing to work on this sort of thing.

Anyway, the power meter will read from about -20 dBm to +10 dBm in 2 bands - HF thru 500 MHz, and from 500 MHz to 10 GHz.  The low frequency sensor is working perfectly.  I got this shipment yesterday.

Today, I built one of the ERA2 dual mmic amplifiers.  I am going to use this as a transmit amplifier to get to the 10 milliwatt level.  10 milliwatts is a magic power level, as many higher power amplifiers are designed to input 10 milliwatts to get you from 1 watt to 100 watts, depending on what you are planning.

The ERA2 preamp boards are tiny as well, but I didnt have too much trouble building this one.  The 0805 chip caps are small, but fortunately, in these amplifiers, they're not too close together, and the circuit for a mmic amplifier is very simple.  These boards are nice high quality boards, made of Teflon, and have plated through via's.  These amplifiers provide about 30 dB of low level amplification, and will output up to 20 milliwatts at the 1 dB compression point.

This is a photo of the amplifier board.  As you can see, it is quite small.  Of course, I have no way to test it until I have the mixer finished.  I am currently working on that now, but I'm short one SMA connector to make that happen.

I still need to finish the mixer, and I also need to make a bandpass filter to place after the mixer that will pass 2304 MHz, but block the 2160 LO and 2016 MHz image.  I am going to use a 3-resonator type filter similar to the one I made for my 1296 rig.  Things start to get rather small on 2304 MHz, the resonators are less than an inch long on this band.  Its a good thing I have a micrometer.  I'll have the filter swept before I use it on the air.  If it's not selective enough, I'll use a cavity filter instead (or in addition to).  2304 is an awkward band in that it is more difficult to homebrew components such as the filters.  Cavities for 2304 are about 1 1/2 inches high, which makes them somewhat on the large size if you are trying to build small.  The resonator filters are less than an inch, and they require some level of precision for them to work well.

Once I get the mixer and filter built, I'll post again, and let you know how it all plays together.  Once I get to the 10 milliwatt level, I may attempt to make a contact on the rig if I can find someone with the capability to operate that band without having to drive too far.

Stay tuned, the next update will be coming soon!

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