This evening I got some more stuff built. I made a CAT interface for the FT1000D which I hope works fine so we can use it in CQWW CW. I’ve been having some issues with the CAT going through the openASC box since the USB is very sensitive against RFI. It might be the computer though since it only happens on the FT1000D, but just to be safe I built an interface for the COM port.
I also finished up the 80m 4-SQ box and built a lid for it. It will need to get some paint to look a bit more pretty though. I hope to install all this during the weekend, so we have a spare 4-SQ box again. But this time with the new lid no condensed water should be able to drip down on the PCB. I will also put a 15w resistor inside the box to keep it a bit heated.
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.
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.
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.