VK4ZXI

IDSG101/GK101 10MHz touchscreen Function/Arbit rary Waveform Generator Arbitrary waveform capability is compatible with The GK101 10MHz touchscreen Function/Arbitrary Waveform Generator is a indigenous-Chinese designed instrument with significant capabilities at low cost. It is part of the emerging Chinese-designed equipment industry where the design is in-house rather than a copy or licenced design from overseas. Historically, this pattern follows Japan and Korea in indigenous design. China educates more engineers each year as the total number of engineers in the UK, so it is perhaps not surprising. At the moment, there is not a lot of English language support for the GK101. I bought my GK101 for US$99 from InstradStudio, the distributor for the AirSpy SDR (Software-Defined Radio),: http://imall.iteadstudio.com/featured-product/im141013001.html . It is available from eBay at a higher price. There is a wiki for the device: http://wiki.iteadstudio.com/IDSG101 . It provides ...

Tuning a commercial UHF duplexer with RigExpert antenna analyser The club is assembling a 70 cm repeater with some equipment kindly loaned to us to use; a Kenwood TKR-820 repeater and a good quality commercial six cavity band-pass duplexer. The tuning was done with a RigExpert antenna analyser that gives a plot of SWR swept across a frequency range. The analyser was able to tune each cavity, but the overall response, while good for separation was compromised, possibly by incorrect inter-connecting cable lengths. Tuning the duplexer The duplexer is a band-pass type, with six cavities, three each for RX and TX with a "T" combiner. The cavities use N connectors and thick LMR400 type cable, and are about twenty years old. The probes are set for maximum coupling, which is desirable for selectivity but for some transmission loss. As a band-pass cavity filter, each cavity has a N connector in and out, making tuning each cavity quite easy; put a 50 Ohm termination on ...

A $300 2m repeater duplexer and cavity resonators-hardware shop special Introduction I have been experimenting with cavity resonators for a 2m repeater for some months now. I had been using aluminium tube and brass fittings. However, with 150mm tube, the optimal antenna should be about 50 mm diameter, with a 3:1 ratio of diameters for impedance and performance. However, the mechanical arrangements and conduction between them became problematic. If I wrapped all the joins with aluminium foil, it worked well, but is not practical. In this post I will outline a new technique that uses shim copper (0.1mm) for all the RF parts. The aluminium tube is lined with copper and soldered to copper shim top and bottom plates, in turn attached to the main aluminium plates. The antenna goes back to a conventional fixed lower section, with a movable section to adjust tuning. The basic premise of the design is still that it can be made from readily available parts at low cost, and with basic wo...