VK4ZXI

Rohde & Schwarz CMU200 Universal Radio Communication Tester resources Introduction This post is a collection of information for the Rohde & Schwarz CMU200 Universal Radio Communication Tester that I have purchased. They can be bought on eBay and other places often for a very reasonable sum. In its day it was an expensive but capable instrument. While the CMU200 is primarily designed for testing now obsolete mobile phone equipment, it can be used for working with analog radio. It has a spectrum analyser, RF generator, RF power measurement and with the option, an audio test set. While not directly having a tracking generator function, there are two PC programs that allow it to be used for testing filters. It can also be done with a noise source or an external tracking generator. The CMU200 uses an embedded Celeron or similar AMD processor running MS-DOS. It has an internal IDE HDD that is wise to replace as the instrument can do tens of thousands of hours. A...

A 70cm DATV DVB-T 7 MHz band-pass filter using a cheap Chinese duplexer Introduction DATV transmitters for DVB-T are notorious for "spread" outside the channel, to the point that keeping it 30 dB or more below the signal becomes a limit for power output, typically 10 W out of a 70 W module amplifier. Even with -30 dB spread, it is desirable to have a band-pass filter before further amplification or transmission. Usually an interdigital filter is used, but they are either expensive to buy or a bit difficult to build. VK4JVC suggested using a cavity filter duplexer instead. I tried a four cavity notch duplexer, but the pass-band losses were too high, more than 20 dB. I had bought a cheap, ~A$100, Chinese Jiesai  duplexer, but had put it aside as the response looked bad. After try other duplexers (notch and pass-reject types), I tried the Chinese one again, this time successfully. The result is that the Chinese filter seems to provide a good pass-band for the 7 ...

Duplexer isolation: limits of instrumentation Introduction With high isolation duplexers, about 100 dB, conventional spectrum analysers and tracking generators are beyond their capability of about 80 dB. The rejection of a high isolation duplexer can be checked using a RF signal generator and spectrum analyser. High isolation duplexers. I have a couple of sets of four cavity 70 cm pass reject duplexers. The two cavities give about 70 dB rejection, which is ok but more would be better for RX. A third cavity can be added for greater isolation. Each cavity is individually tuned with a spectrum analyser and tracking generator. The two cavity duplexer can then be assembled and tested. A nice plot with about 70 dB rejection at 438.1 MHz and a pass of 433.1 MHz. Adding the third cavity results in noise at the rejection notch. The spectrum analyser cannot show the full depth of the notch; it does not have enough dynamic range. RF generator and spectrum analyser A RF...

Improvised DVB-T test instrumentation My last post was on snooping on DVB-S signals from satellites. I found some useful software to do that, Crazyscan and Blindscan. However, the author of Crazyscan also wrote Crazyscan 2 for DVB-T but needs specific TV hardware:   http://sourceforge.net/p/crazyscan/wiki/Info/ I ordered a TBS 6220 (DVB-T) (~$100) as well a TBS 6925 (DVB-S) (~$300), both pci-e cards, direct from the manufacturerhttp://www.tbsdtv.com/ . With courier delivery, they arrived within a week. Setting up the TBS 6220 is straight forward and works well as a TV card with DreamTV; mainly to confirm that the device works. I put both cards in and software for both, but things got messy. Removing the TBS-6925 and its software, including auto start programs, fixed everything. I need to walk before I run. My interest is with Crazyscan2. Setting it up is easy, just putting all the needed files in the same directory. The result is amazing: a scan over 1 GHz at 1 ...

BladeRF on Haswell i5 running Windows 8 with SDR-Console at 935 MHz 20 MHz bandwidth Screen shot of BladeRF running on Windows 8 with i5 Haswell processor. The BladeRF windows installer uses an unsigned driver. With the extra security of Windows 8 it will not normally even give you the option of installing unsigned drivers, Windows 7 does. However Windows 8 has a special restart where the unsigned driver block can be disabled. I think I described it in earlier blogs. Using the earlier beta of SDR-console V2 per earlier blogs, the bandwidth is 20 MHz rather than 30. I think the narrower bandwidth is more appropriate re Nyquist, about half the 38.5 MHz bandwidth of the BladeRF. At 20 MHz, the CPU is barely busy at about 4 % versus 10 times that of screen shots at 30 MHz in earlier blogs. Simon Brown, the author of SDR-Console said in his Yahoo forum that the FFT runs at 30 MHz too. Dropping the bandwidth to 20 MHz seems to calm everything down.   ...