Any idea how much attenuation in the MW filter, or a picture of return loss, etc? The protection circuit has a lot more to the description...curious about some of the MW filter specifics.
Thanks for offering these! I had already ordered the protection board, thinking I'll have to do something for MW attenuation when I upgrade to a larger loop antenna, too.
I have one of the Noolec MW filters, and I might get one of these to try.
I've posted this before, however there does seem to be two schools of thought.
I'm using the MW filter in line with an LNA. I have to use the MW filter before amplification, otherwise I end up with MW reflections up into the 160mtr band (if I have the MW filter after amplification.)
I'm using an LNA due to limited space for a larger antenna and local noise in an urban area.
I'd be interested to see some results in these situations? (ill order one anyway)
This is an embed external element. It can be deleted using the delete key or the backspace key. To view the full element, press the preview button below.
There is never any "one size fits all" solution when it comes to filtering. If you're serious about 630 m, where you don't want any attenuation of weak signals, you should never be looking at a full MW bandstop filtering solution. You're never going to spare a frequency segment that close to 530 kHz.
You're probably best served by high-Q series LC trap(s) on the problem frequencies. That's something you'll most likely have to build yourself. But it's about the simplest thing there is.
You only need sufficient attenuation to take the strongest broadcast stations down by just enough to prevent ADC overloads from occurring. I generally try to keep all signals across the 0-30MHz spectrum below -30dB.
If you have an existing band stop filter, with too much attenuation, you can connect a 1K ohm variable resistor between the input and output of the filter, and then adjust the value until you have enough attenuation to prevent overload occurring at night, but still allow some signals to pass through at a usable level.
Even on a receive site where I had strong signals from local medium wave transmitters, I've not had to introduce more than 20dB of band reject filtering to fix the problem. In most cases, a simple 10dB slope frequency / amplitude equaliser provides a good compromise.
This and other techniques have been discussed in many previous threads, so it's worth searching for those.
I dont think anyone here in NZ uses the 630mtr band, however typical MW broadcasts are insanely powerful, and find the Kiwi filter attenuates rather than just cuts them out, meaning you can still DX MW without overloading your SDR when using an LNA, which is my case.
I know the majority of Kiwi owners are only interested in HF, but there are many of us who do a lot of MW DX. The network of public Kiwis are highly useful for trying to track down a weak MW station, especially one that doesn't have an online stream. Using my own Kiwi and comparing to another Kiwi, you can often hear the 1:1 echo of a station between the two SDRs. So its unfortunate to see once really good Kiwis in desirable areas suddenly go "deaf"...or so you think until you zoom the waterfall out and see VLF and HF are as alive as can be and it's only the AM band that is deaf 😖...
So instead of implementing an MW BCB filter, I'd encourage trying a few dB of attenuation or try constructing notch filters for those specific problem frequencies.
A couple more once good Kiwis, including one out in California I often used, just tossed MW filters on them within the past month or so.
Net on thursdays @ 8:30 pm and I use my kiwi with the am filter for recieve. presently I do not transmit as I cannot load the extended double zepp for 80m 0n 160 or 630m a new 390m doublet is about to go up and I'll be present on those bands on TX
This is an embed external element. It can be deleted using the delete key or the backspace key. To view the full element, press the preview button below.
Comments
Any idea how much attenuation in the MW filter, or a picture of return loss, etc? The protection circuit has a lot more to the description...curious about some of the MW filter specifics.
Thanks for offering these! I had already ordered the protection board, thinking I'll have to do something for MW attenuation when I upgrade to a larger loop antenna, too.
-Nate
N8BTR
I didn't design these. Ask sales@kiwisdr.nz
Heres the MW filter response thanks to ZL2J the designer
I have ordered two of the band stop filters to try. Hopefully they will not attenuate the 630 band as much as the nooelec filters.
73
Steve KD2OM
I have one of the Noolec MW filters, and I might get one of these to try.
I've posted this before, however there does seem to be two schools of thought.
I'm using the MW filter in line with an LNA. I have to use the MW filter before amplification, otherwise I end up with MW reflections up into the 160mtr band (if I have the MW filter after amplification.)
I'm using an LNA due to limited space for a larger antenna and local noise in an urban area.
I'd be interested to see some results in these situations? (ill order one anyway)
New product accessories in our store: SDR protection circuit, MW filter
https://forum.kiwisdr.com/index.php?p=/discussion/comment/20454#Comment_20454My filter arrived today, and I must say it is better than the Noolec MW filter. I put it before the LNA, as this works the best.
The MW stations are still there, unlike the Noolec filter would kill everything from the VLF up to 1.8mhz bascially.
I'm glad that you like the filter it should give 120dB of third order intermod suppression to AM band signals ZL2J
I tested both filters with a network analyzer. Here is a simple comparison of the Kiwi filter to the Nooelec filter,
160 to 10 meters both usable.
MWBC the Kiwi filter has > 10 dB more rejection than the Nooelec.
630 meter band the Kiwi filter is unusable due to higher rejection. The Nooelec has some rejection but is usable.
2200 meter band, both have similar rejection, about 10 dB, so somewhat usable.
There is never any "one size fits all" solution when it comes to filtering. If you're serious about 630 m, where you don't want any attenuation of weak signals, you should never be looking at a full MW bandstop filtering solution. You're never going to spare a frequency segment that close to 530 kHz.
You're probably best served by high-Q series LC trap(s) on the problem frequencies. That's something you'll most likely have to build yourself. But it's about the simplest thing there is.
You only need sufficient attenuation to take the strongest broadcast stations down by just enough to prevent ADC overloads from occurring. I generally try to keep all signals across the 0-30MHz spectrum below -30dB.
If you have an existing band stop filter, with too much attenuation, you can connect a 1K ohm variable resistor between the input and output of the filter, and then adjust the value until you have enough attenuation to prevent overload occurring at night, but still allow some signals to pass through at a usable level.
Even on a receive site where I had strong signals from local medium wave transmitters, I've not had to introduce more than 20dB of band reject filtering to fix the problem. In most cases, a simple 10dB slope frequency / amplitude equaliser provides a good compromise.
This and other techniques have been discussed in many previous threads, so it's worth searching for those.
Regards,
Martin
I dont think anyone here in NZ uses the 630mtr band, however typical MW broadcasts are insanely powerful, and find the Kiwi filter attenuates rather than just cuts them out, meaning you can still DX MW without overloading your SDR when using an LNA, which is my case.
I know the majority of Kiwi owners are only interested in HF, but there are many of us who do a lot of MW DX. The network of public Kiwis are highly useful for trying to track down a weak MW station, especially one that doesn't have an online stream. Using my own Kiwi and comparing to another Kiwi, you can often hear the 1:1 echo of a station between the two SDRs. So its unfortunate to see once really good Kiwis in desirable areas suddenly go "deaf"...or so you think until you zoom the waterfall out and see VLF and HF are as alive as can be and it's only the AM band that is deaf 😖...
So instead of implementing an MW BCB filter, I'd encourage trying a few dB of attenuation or try constructing notch filters for those specific problem frequencies.
A couple more once good Kiwis, including one out in California I often used, just tossed MW filters on them within the past month or so.
SMG I do use the 630m band here in NZ
Net on thursdays @ 8:30 pm and I use my kiwi with the am filter for recieve. presently I do not transmit as I cannot load the extended double zepp for 80m 0n 160 or 630m a new 390m doublet is about to go up and I'll be present on those bands on TX
73 ZL2J
New product accessories in our store: SDR protection circuit, MW filter
https://forum.kiwisdr.com/index.php?p=/discussion/comment/20629#Comment_20629Oh good to know! Still a lot to learn! :-)