People might think I am crazy building all these filters all the time. But I think it’s really fun and I learn a lot by doing it. Now I think as I wrote in the previous post figured out how to do the filtering at the station. These RX filters will sit in the RX-path of the transceivers and I might do so that they are switched in depending on which bands the other radios are on. For example if the run station is on 20m then the 20m filter will be switched in on the mult stations and if one mult station is on 15m then that filter is switched in on the other mult plus also the run station. That way I will have the least amount of insertion loss possible, since it’s no need to use filters on bands which does not have any radio transmitting on them. Not that the insertion loss is high, but every 10th of a dB counts, at least in my opinion.

I first tried to build the filter on a PCB that I milled but it was extremely hard to tune it and I could only blame it on coupling between the filter nodes and I did not get near the performance that I expected from simulations. The filters are 5-pole chebyshev notch filters. So to test my theory I built a box with chambers and added pole for pole into it and measured and already with three poles I beat the old result and a lot better insertion loss as well. When adding two more poles the result was close to the simulations and I am very pleased with the performance.

Now I need to figure out if I should be pleased with just three poles or if I should go for 5 poles, we will see. I think I will make a bunch of filters in a big box and make chambers for it, will be a lot of work but I think it will be a great result and totally worth it. But I will make another test first, and that is to use toroids on all five inductors and that way maybe the coupling will be so low that I don’t need to use chambers, it’s worth a try because it would make it A LOT easier to build them.

I also put a Webswitch which we got sponsored from Microbit 2.0 AB into a box, that will be used at the station to be able to switch gear on and off over ethernet. That way I can reboot stuff if needed and not needing to have power on to the openASC system the whole time etc.

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Today we spent some time to get the rotator up in the WARC tower working. So now it turns the 5el 20m beam but it does it very slowly, it takes three minutes for a whole lap so I will need to run it on 24v. However for the contest I will run it as it is since I don’t have a 24v supply which can supply enough current to rotate it. Anybody have one that they dont need? I also need a new 13.8V supply which can supply 10A or more.

In the evening I hooked up the filter switch i recently built. Its connected after the amplifier and puts in notch filters depending on which band we are on. Currently I have filters for 80,40 and 20m. However the 40m filter need to get some notches added to it to notch away 15 and 10m as well and not just 20m as it does now. I will also need to build a 160m filter that notches away all bands except 160m.

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I have finally decided how to do all filtering at the station. Right now it works quite OK, we don’t suffer from too much problems but I believe it should be possible to totally get rid of all harmonic problems etc. When I connected the 80m notch filter I built I noticed no change, which made me convinced that the current problems are in the switching system. So I decided that the filters used to suppress harmonics will need to be placed directly after the amplifier before the antenna switching. So I decided to build a pair of 1×4 switches used to connect the harmonic suppressing filters for 160,80,40 and 20m. I regret not making it 1×5 though, to have one position which bypasses the filters (15/10m), so I will need to use the 160m position for that until I fix another pair of ports.

The other idea is to make a few RX only notch filters. I will make one set of filters for each band and connect all in series except the filter used for the current frequency will be bypassed. That way I can have huge attenuation on the main signals and when also suppressing the harmonics the station should be very well protected against QRM between the bands.

There are also some pictures of how it looks at my land now when the forest machines have been on it. A lot more room now for the new 60m tower.

Tomorrow I am going down to the station to prepare for the CQWW CW contest. SM2XJP went down to SM3 land to pickup another MKV that I bought so now the setup will be 2xFT1000MP MKV which I am really excited about. SM2LIY is at the QTH trying to get the beverages ready for the contest which I will do as SOAB for the first time since WPX SSB last year. This is the first SOAB CW I do on CW for a long time, so hopefully I am not a total lid.

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