Sunday, October 31, 2010

2304 MHz Transverter - Significant Progress Made #1

Welcome back!  Today was a good day.  Got a LOT done on the transverter with the help of WA3TTS.  There was so much that we did, I can't write it all in one post, or in one night.  I'm going to split this up into several postings.  Question is, where to start.

First thing, and probably a very important thing is we checked the LO level and spectrum.  The level is much lower than I expected, I'm getting about -3dB at the SMA connector on the receiver brick.  The good news is it is VERY clean, all spurs are down by more than 60 dB, and the nearest spur is over 100 MHz away from the intended LO freq.  My plans have changed slightly because of this.  Since I have 2 of the Down East ERA2 2 stage amplifier boards.  I plan on taking the unbuilt board, and cut it in half, making 2 single mmic boards.  I will then use one of these boards to amplify the LO.  These boards should have about 15 dB of gain, so I should get about 12 dBm out of the amplifier, enough to properly drive the mixer.  I'm certain that if i fiddle with the LO probe, I could increase this level, but since the LO is so clean, I am almost tempted not to mess with it.  At least I know how much RF is there, it wont be difficult getting the level up to where it needs to be.

While I was there, I finished the mixer module.  We added a filter (more about this on the next post), and measured -20 dBm at the RF port of the mixer.  We only used the available -3dBm from the LO source.  A signal generator simulated the IF, tuned to 144 MHz.  The mixer output saturated at +6 dBm.  I believe that when I increase the LO level to +10 - +13 dBm, the output level will increase dramatically.

We did not test the 2 stage low power amplifier.  It is ironic to think however, that the -20 dBm coming out of the mixer matches perfectly the 2 stage gain of 30 dB, and in theory, I would end up with the +10 dBm that I'm shooting for at the output of this amplifier.  I believe it would be better, however to drive the LO to the +10  dBm level and run less IF energy into the mixer, thinking the linearity would probably be better coming out of the mixer.

As you can see from what is presented here, the rig is almost ready to hook to an antenna.  All that it needs is a good filter following the mixer, and perhaps a bit more power.  Tomorrow I'll write about a filter that we retuned and some of the really cool features of this filter.  We'll also talk a little bit about power amplification too.  I'll leave the cliffhanger here... Lets just say, I got a solid state power amplifier that will provide meaningful power for portable work.  It will need some work to get it to run on 2304, so will be experimenting with that soon also.

Stay tuned, keep the dish pointed this way, and check this frequency soon for the next update.  73 for now.

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