Monthly Archives: May 2011

Notch filter built and isolators made

I’ve done some work in the lab again. We’ve been seeing some QRM on 10m from 20m, so I decided to built another notch filter. I am very happy with the result, about -86dB notch and around 0.01dB insertion loss on 20m. I also spent some time in the lathe making some isolators for the 40m verticals for the 4SQ.

I really recommend these notch filters. They work great and are very easy to build. I start with making the stubs a bit too long. Then I cut them until I have the notch at the correct place. After that its a matter of decreasing the insertion loss, so I adjust the L until I get rid of the C from the stubs, giving a perfect 50 ohm match.

Outdoor work

I went to the QTH on Thursday evening with a bit of fever with my girlfriend, which luckily got better as the weekend progressed.

A lot of time was spent outside this weekend. On Friday me and SM2XJP went to Robertsfors to pick up some aluminum that was ordered a while back. Unfortunately our big order of almost 200kg of aluminum has not yet arrived, but hopefully it will within a few weeks. We also paid a visit to SM2DMU/SM2HTF QTH were we also met SM3DMP who came by on his drive to a dog show further north.

On Friday night SM3JLA showed up while I was fixing so that the 4-1000A PA was easily switchable between 160-20m again (It does not operate on 15/10m). We fixed some stuff for WPX CW next weekend and on Sunday we spent time digging holes and putting down the support posts for the 40m 4-SQ, which is now ready to go up. However we need to clear away some cut down trees before we can put out any radials.

I also spent a few hours cutting down trees making a road for the crane so it can reach the place we will put up the 40m high tower. Still a lot of trees to take down and plenty of work getting rid of all the cut off branches and logs, but we are making progress.

4-SQ box for 40m finished

I’ve built a phase box for the new 4-SQ. It’s built on a PCB I designed a couple of years ago for SK3W and I added a nice little text to it, just for fun 🙂 The cores are two pcs of T300A-2 and the capacitors are Russian doorknob, about 200pF in each capacitor bank. I’ve measured a bit on the oscilloscope and it looks like it performs as it should, so hopefully soon we’ll get to test it on the 40m 4-SQ. I haven’t decided yet if I am gonna make a box for it. It will be installed in a cabinet so weatherproofing is done, I might add some metal around it just for shielding.

I also spent some time in the lathe to make the tubes fit for the WARC duobander I’ve designed. It’s an Hy-gain LJ-203BA which I shorten the elements so that it operates on 17m and I added four elements for 12m to it as well. To avoid needing to calculate the effect of those strange Hy-gain element clamps I will replace them with my own and isolate the elements from the plates.

Rumors this weekend is that SM3JLA will show up and I hope we will go and spend a few hours in Skellefteå at their flea market that the local club SK2AU arranges. I am going down to SJ2W on Thursday evening and will start shoveling gravel to fit the posts for the 40m 4-SQ.

New antenna switch design

I received some PCBs I had ordered from China today and decided to make a box out of aluminum so that I could do some measurements and see its performance. I had done a 6×1 design before but I did not have any easy way to compensate for the stray capacitance in the box, making the insertion loss a bit too high for my taste on higher frequencies. Now the new improved design will hopefully be a lot better and I will measure it hopefully tomorrow in the network analyzer at work.

I will put this box inside the amplifier room at SJ2W so that I can easily route non-contest antennas (6m, WARC etc) to the radios without needing to put long coaxes out to the switch room in the barn. We are planning on putting up a tower for WARC and maybe some fixed contest antenna as well and that will be located quite close to the house, making the cabling quite easy to get into the amplifier room. I have an old Hy-gain 3el yagi for 20m that I will rebuild for 17m and add 4 elements for 12m on the boom as well. Plus I have designed a 2el for 30m designed to survive 40 m/s winds which will be put above the duo-bander.