Sunday, June 23, 2013

Pipe cap filters for 10GHz

The most common problem in a transverter system is local oscillator leakage, this is the local oscillator signal get through the TX mixer to the power amplifier chain, becoming present at the antenna connector at some level. LO leakage is usually a sign of poor design, but it can occurs also by defective or wrong shielding or even by a metallic enclosure box.

In my case the problem was the metallic enclosure used for the transverter. With the cover removed everything was fine but once the cover was put in its place, the local oscillator was present at the output at nearly 5mW of power: Just unacceptable.

Wednesday, June 12, 2013

Using the Eyal Gal 10GHz module in a ham radio transverter

The core of my transverter project is a 10 GHz Eyal Gal module acquired in eBay the last year. These units have a receiver converter and a transmit power amplifier in the same enclosure.

Because the design frequency of the module is 10.4 to 11.7 GHz, it works unmodified at 10368 MHz, which is a clear advantage for use at ham radio.

There is not too much information about these modules except the info published by G8CUB here and herethis post from M0DTS and this datasheet. It is convenient to read all these documents before continue reading this post.

Friday, June 7, 2013

Setting the output power in Yaesu FT-911

Recently I have been using my Yaesu FT-911 as signal generator to test a 10GHz transverter's local oscillator multiplier stage (1242 x 8 = 9936 MHz). Everything worked fine, but the readings I had were not consistent. The output power was lower than expected.

When supplied at 13.8 volts, high output power should be 1W, but I was measuring around 550mW. Clearly something was wrong. Many time ago, when I purchased the walkie, I did a quick readjustment using an attenuator and a spectrum analyzer. Spectrum analyzers are fine to see spurs or relationships between carrier and harmonics but they are not good as absolute power meters, specially if you are using them at the top of their dynamic range, this is with insufficient attenuation between.