Category Archives: Electronics - Page 28

TX/RX Relay for the Granger

Posted by sm2wmv on November 14, 2011 Comments Off

Today I built a TX/RX solution for amplifiers. It’s mainly built for the Granger amp we are using (4CX1500B, about 1kW output) most of the time. This amplifier seem to have some attenuation through it, I don’t know how much but you can hear the difference when switching between the amps that its more attenuated. So instead of rebuilding the circuitry inside the amp itself I just built an external TX/RX relay. This also deceases the length of cable, not by much since its only 10m but its 10m that doesn’t need to be in the path on RX.

I got 0.1dB insertion loss through the RX path. Not perfect by my standards but it will have to be good enough and probably a lot better than how it currently is.

[Show as slideshow]

More electronics built

Posted by sm2wmv on November 12, 2011 Comments Off

Today I spent a little time at work finishing up the notch filter (hybrid lowpass filter from the W2JVN book). I put a fan on it to make sure nothing burns up while doing digital modes for example. I also built a holder for some W1W vacuum relays. I have run out of W2W relays so I ended up using these instead and will put two in parallel so that they will handle the current. Its for adding more capacitance to 160m in one of the amps that will get QRV on 160m now as well, so that we just don’t have one amplifier on that band. I will also replace the current relay which is used to connect the pad capacitor for 80m.

[Show as slideshow]

Some notch filters

Posted by sm2wmv on November 11, 2011 Comments Off

I built a couple of notch filters today. One which I intend to use just to test if the overtones when transmitting 80m is what is causing the problem or if its the actual 80m signal that is too strong for the receivers to handle. So if I insert this notch filter which provides about -61dB notch @3.65 MHz and the problem still occurs, then its the overtones which are the problem.

The notch filter is a 3-pole Chebyshev filter which I designed with Elsie. I should get a bit more notch by fine tuning it but I need to get hold of some decent trimmer capacitors. I noticed when I changed the fixed capacitors from regular ceramic ones (X7R or similar?) to NP0 I went from 18dB notch to 30dB (!) when measuring on a part of the filter, that is quite some improvement. So the conclusion of this is, NP0 rules!

I also built a hybrid lowpass-/notchfilter that I’ve built before for 40 and 20m. I really like these filters! They are easy to build, they have great overtone attenuation and they handle legal limit with a big margin. However, this filter I didn’t get as good as the earlier ones, probably because the stubs work less well the lower in frequency you go. I managed to get around -60dB of attenuation on 7.1 MHz but what I got disappointed about was that I didn’t get the attenuation through the filter down more than to 0.15dB.

[Show as slideshow]

Some remote control stuff

Posted by sm2wmv on November 3, 2011 Comments Off

I worked some tonight on a card which will be essential for the remote control of the station. This boards will talk to the server via USB and has got an openASC bus so it can talk with devices on the bus. It will also control the relays that turn on/off gear in the shack. That way I don’t always need to have everything running, just the server and this small board. So when I want to work remotely there is a software on the local PC that will be used to turn on/off the gear and you’re ready to go. This has also got a timeout, so if it hasn’t received a ping within a certain amount of time, all the equipment are shut off. That way there is no chance for the radio to be stuck in TX if we lose internet or similar.

There is also a picture of the 80m 4-SQ box which I burned up just prior to the contest. When I walked out to the 4-SQ, about 40m from it I could smell the burned electronics and the board was too damaged to be fixed. Luckily I hadn’t given back the 4-SQ box we previously used, which was borrowed from SM2NOG, so I installed that and we were ready for CQWW DX SSB which turned out great. There was some water lying on the board so I suspect that is why it flashed over, and when things start to go bad it burns quite quickly. Next version I will put a better box and also a 15w resistor inside it to keep out moisture.

Hopefully this weekend we can get the 18m tower up and during the evenings I will try to work on the remote control stuff. Would like to be able to listen around a bit during the weekends, even if I can’t rotate antennas yet I can change bands and control direction of the 4-SQs etc. through openASC. Next thing after this will be to start installing the rotator boards into the rotator control boxes.