VK3AQZ Kits Attenuators

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I ordered these kits on Monday and had them in my hands Tuesday, nice work overnight express delivery. Bought from VK3AQZ Kits for $20 each plus post. I would be hard pressed to Ebay the parts for these and come in under that cost and then they would not look as professional and well made as these with their machined cases and chromed labels.

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The 2 kits i bought give a total of 10 and 50 db of attenuation, the first gives 1, 2, 3 and 4 db of attenuation.

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The 2nd gives 10, 20, 20 db of attenuation. They are rated to 250mw and 50mhz. But, with paralleling the shunt capacitors you can make these 1w, either way, for just about every application one might use these for in their homebrew projects, they are more than adequate for the job at hand. Form 3db points on filters and resonators, to 10 and 20db points to align the rf meter, to noise testing and the like. Attenuators are handy kits to have.

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Kits go together very easy.

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RFPM1 RF Power Meter Part 2

RFPM1 RF Meter Kit by vk3aqz Kits.

Ok, so a quick update on the RF power meter, I have got it complete, I did not take as many pictures as i should have. The kit is super easy, the instructions are brilliant, the packaging brilliant and the service from Lou the kit maker, just awesome. I cannot fault any aspect of this build, it has all been super clear and easy. The videos of the build process show everything you need to know, and the alignment videos are superb and make things so simple and clear.

All i have left to do is smoke test and align the meters and power head. To do that I need attenuators, and for that, I will write another blog post, as i bought 2 attenuator kits also from VK3AQZ kits.

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SMD part in the RF power head are easy enough to solder, not a huge fan of doing it, but nothing a bit of liquid flux wont make easy.

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RF power head assembly is rather straight forward. The video instructions make things very clear here.

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Now i did not take any pictures of this as it went together, totally forgot, but the build is super simple and the use of JST XH connectors throughout makes for a nice clean wiring job.

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The unit fully assembled, ready to smoke test and align.

 

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Only job remaining after alignment is to add the handles, and feet to the case and then use it often in projects. All in all, very happy with the quality of the build. I cannot wait to get it aligned now and to use it on my projects.

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Bye Bye IC-718

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18 months ago i became an amateur, my first radio was an IC-718, it was about all i could afford at the time. It has served me well and been very reliable, but all good things must come to and end and for radios there comes a time when you upgrade.

In the last 6 months i have gotten into CW. And anyone who has tried CW with a barn door receive knows, just how painful it can be without a good CW narrow filter. So my options became spend $350 on a Icom narrow filter or upgrade the radio to one with IF DSP. So, I will soon be the prowd owner of an IC-7410. Yes im an Icom fan, the menu structure feels familiar and uncomplicated. I do also own an FT-897 and to be honest i have never really felt comfortable with this radio and for CW it has always felt hideous and the AF DSP rather disappointing.

So my last QSO on this radio was today with special event call VI2AJ2016 who was in Sydney Australia on 40m. This special event call is for the Scout Jamboree. Thanks and bye bye IC-718. May your new owner enjoy you very much.

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455khz IF Filters Part 4

Ok, so the journey continues, what i did the other night was to redo the motional parameter measurements of the ceramic resonators and plug them into a different program to design the filter called Ladder Filter Crystal Design.

 

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One thing i did this time was to use a larger value for Holder Capacitance, 100pf, as i was informed that ceramics typically have a Cp in the 100 to 200pf range. the design parameters are 4th order Butterworth with 400hz bandpass.

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I built the filter on a scrap of board, having drawn the schematic as in the picture last night, but remembering there was a small difference in the values of C1&7 and C3&5 I built the filter using 68pf for C1&7 and 82pf for C3&5 which was backwards to what the program predicted, and 480pf for C2&6, 10pf was used for C4, as per the design.

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Filter response was plotted and it actually looks like a filter. The Centre frequency and bandpass are actually close to where they need to be, and this might be something i can tweak now into a usable filter. More work to come, but, i have made some progress.

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455khz IF Filters Part 3

So i have these LTW455IT ceramic bandpass filters in my parts box, 455kHz Bandwidth +/-2kHz at 6dB with 6db insertion loss. So i thought i would plot out its response to see how it looks, and to be honest it is very close to spec, but a little bit high in freq, centre should be 455 + or Р1khz, mine showed a centre of 457khz, 2khz higher, now i did not impedance match to 2K ohms, but i probably should have. (BLUE Graph Line)

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So i thought to myself, if one is good, two must be better and then plotted out the response (RED GRAPH) The added capacitance pulled the freq down closer to 455khz. Each filter is 6th order so this essentially made a 12th order filter, I kind of expected the skirts to steepen, but they did not, I do not know why, but i would like to find out.

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Measured with the signal generator on the input and scope on the output with the grounds connected together, isolated from the filter grounds. I did connect the filter grounds together but was getting strange readings, i think you have to use dc blocking caps on the output if you use the inbuilt ground pins.

Anyway, it was a little bit of fun, that did not amount to much other than one of these filters would make a nice narrow SSB filter for a tranceiver that has a 3khz or larger front end bandpass.

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455Khz IF Filter Part 2

So in moving this forward some, i decided to knock up a 4th order filter based on the Dishal parameters, and then plotting out the filter to see how well theory and reality collide.

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These were the settings i used in dishal based on previous experiments.

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This is the filter realized, 2nf were used for the 1984pf and parallel 1nf and 580pf for the 1708pf capacitors.

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Test rig was scope on output and function gen on the input, i did not worry about impedance matching 50ohm to 150ohm.

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Measurements were taken every 200hz and plotted in a spreadsheet. A couple of things, firstly there are 2 peaks not sure why, second major one is the filter is 2K wide not 400hz wide, might almost work as a narrow SSB filter HIHI and the third major issue is the center freq is even lower than predicted at about 442 -> 443 Khz, no where near the 447 predicted and still miles away from 455Khz where the radio’s IF is.

This has been a very useful experiment, I think i can improve on this first effort by a long margin and I intend to go back the the drawing board and see if i can get more accurate motional parameters and also if i can pull the frequency UP somewhat with added capacitance to get this thing closer to 455Khz.

 

filterplot

Ok, so as an addendum to this, i terminated the filter at 150 ohm, turned the power on the function gen right down to its lowest setting and this is how the filter now looks.

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