Simple Low Pass Filter Design For Minimalist QRP Transceivers or Transmitters
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- เผยแพร่เมื่อ 9 ก.ย. 2024
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A simple way to improve the existing PiNetwork low pass filter in minimalist QRP transceivers or transmitters like the Pixie. In my case in this video I am concentrating on a simple CW transmitter.
73, YO6DXE
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Try increasing inductance to 1.6uH.
For simple filter as it is it's working great, if you want greater results you can try 3 stage filter where you have 3 inductors and 4 capacitors. I have cw transmitter and i am using same 3 stage one. so first and last capacitors are 470pf and middle ones are 820. First inductor is 1.6 second is 2 and third is 1.6. i think this configuration with little changes can almost suppres harmonics
The one with three inductors for sure it works way better. I build one in the past with only two inductors and three capacitors and it was doing good already. The reason why I want to see how good the Pi Network filter can get is because all simple transceivers have it... because is really simple I guess. But useless as it seems ))). So to keep things just as simple as they are I am trying to get the best out of it and still keeping it simple. Fingers crossed it works haha. 73 my friend.
@@dxexplorer you know sometimes simple solutions have limits. that's why they invented 2 or 3 inductor version.
@4L1LAT yes of course. That is for sure. But you know... when someone spent so much time in the past to come up with some extremely simple schematic for something that works really nice... it would be nice to keep that simplicity. Feels good to make something out of nearly nothing 😁. The fun part is how far we can push those limitations. The joy of QRP and homebrew stuff at the end 😅.
Very nice
So happy with the filtering now. It was a mess with the Pixie style one.
можно снизить индуктивность до 855nH и поднять емкость до150pF и добиться подавления второй более 50dbm при практически отсутствии потерь на рабочей частоте, но полоса подавления на таком фильтре получается узкой, порядка 150khz при -50dbm))
Ohhh for a fixed frequency transceiver or transmitter it wouldn't be bad at all. 😁😁😁 I have to try it.
@@dxexplorer даа, но это уже скорее спортивный интерес, гнаться за таким подавлением в таком маломощном передатчике особо смысла нет, уже при 40dbm подавления, ваши гармоники услышит разве что приемник лежащий рядом на столе)))))
I was really curious to do a test on websdr to see if it can be heard in 14MHz. I also think that it can be heard near the receiver, being so close, but already at a distance, the signal disappears completely, being so weak. I am now waiting for some tests with TinySA because I am very curious.
@@dxexplorerпоигрался я с этим режекторным фильтром, попробовал с колечком amidon Т37-6(желтенькое, осталось от конструктора trusdx) 16 витков провода 0.5мм и с конденсатором 160pf, а дальше подстраивая растяжением сжатием витков подстраиваем под частоту подавления, в моем случае вышло под -70dbm подавления на частоте 14060, но настроика чувствительна, без приборов такое точно настроить сложно,да и витки потом желательно чем то зафиксировать)))
@piterstein9625 Ohhhh wow. Excellent results. Yes indeed is a little harder to adjust it with ought measurement equipment. But it seems that even with the 1uH inductor made on T37-6 and the 130pF in parallel does a good job. I keep testing it and if I place the transmitter 20 centimeters away from the transceiver the signal is gone completely on 20m. So it must be a good sign I guess. Not sure about the third harmonic, but I will test that one too later on today on another receiver. Thank you for doing the test. I really appreciate this. 73, YO6DXE.
Its not as si.ple as sticking a low pass filter on the end of a transmitter. It needs to match the output impedance of the final transistor. This could be quite low. If its a tube it could be quite high. Either way we need to calculate to match into a 50R load.
The filter is simulated as 50 Ohm in and 50 Ohm out... I think the only way to adjust the output of the transmitter / transceiver is by adjusting the value of the output capacitor. I have no clue I am not that wise (ha). But this is what I've seen in the past that the more experienced than me that used to do. The Pixie and these simple things I make are pretty much the same it seems. Or maybe an impedance matching transformer ? Thanks Nigel.
@dxexplorer just use a filter calculator and adjust the source impedance that way. It's the only way you can transfer the full energy available out to the load or antenna in our case. Otherwise, you will lose energy in the transformation irrespective of spectral purity. Most filters published on the interweb assume 50 in and 50 out. It's simply not the case as an add-on. Unless the final output has a designed impedance of 50R.
It's like putting a 32R speaker on the output of an audio amp designed to drive 4R speakers. It works but nowhere near as good as it could.
@multilecful yes indeed you are right. Technically the designs were published as having 50 Ohms out... so in theory I should be ok. But it doesn't hurt at all to calculate and see 😁. And here we are I must ad one more beer for you to the list 😅😅😅.
Hi. Nice video. If I get chance I will build your filter and test it. 73 Paul
Morning from Transylvania. Ohhh that would be great. Thanks so much Paul. On the nanoVNA it seems fine... not sure if in the transmitter does a good job too 😁. 73, YO6DXE.