Notch Filter Recommendation

megascanner

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I have a HPN-30118 Combined Notch Filter, which I use with a roof antenna for reception on the BCD536HP scanner. But I recently purchased the SDS100 handheld unit and wanted to occasionally hookup the external antenna. What's the best notch filter for hooking up two scanner radios. Even if I keep it hooked to just the base model 536HP, is the HPN-30118 still the best option in terms of performance and filtering? I would never use both radios at the same time but it's easier to have an extra cord rather than unplugging the base unit al the time.
 

jonwienke

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You're confusing two different things. You want a multicoupler if you want to connect two or more receivers to a single antenna. Put the filter between the antenna and multicoupler, and then you're sending less garbage signal to the multicoupler. Multicouplers have multiple outputs (anywhere between 2 and 16) for connecting multiple receivers. Stridsberg makes a nice range of units, you might want to consider the 4-port model so you can connect both scanners and maybe a SDR dongle or whatever, too.

Regarding filter performance, the best filter depends on what frequencies you are trying to receive, and which frequency(ies) are potentially interfering. Without knowing that, it's impossible to give useful recommendations.
 

Ubbe

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The HPN filter are a good one that doesn't attenuate VHF air frequencies that some other filters do.

If you never intend to use both scanners at the same time, then put a T bnc connector at the 536 and and a second coax from that to the SDS100. Keep the 536 turned off and it will not interfere with the SDS100 reception.

The problem with that solution are that when you use the 536 and it still has that extra coax connected to it, the coax will work as a notch filter for certain frequencies depending of the lenght of the coax when there's no load at the end of it. You will need to terminate the coax with a 50 ohm load to prevent that.


/Ubbe
 

jonwienke

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That arrangement drops the signal a minimum of 3dB.
 

iMONITOR

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I just received a PAR VHFBP filter yesterday from Universal Radio. I'm going to play around with it on my dedicated VHF Aircraft scanner (BCT15X). It does more than the typical FM-Notch filter.

1598071876835.png
The Par VHFBP is a special bandpass filter designed for the VHF aero band listener. It passes the VHF civil aeronautical band 116 to 134 MHz and blocks other frequencies. Unlike other aerocom bandpass filters, the VHF-BP not only provides protection from VHF pagers, NOAA, 2 meter amateur signals etc., but also offers excellent attenuation of the FM broadcast band - the primary offender of aerocom signals. BNC female input and BNC male output.

WNIC FM 103.3 out of Dearborn, Michigan hits my home pretty strong. Pager signals are plentiful around me as well.
 

Ubbe

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That arrangement drops the signal a minimum of 3dB.
When you turn off the 536 it goes high ohm and doesn't load the coax. When it's powered on different switch diodes will conduct and switch in different band filters that loads the signal with different impedancies, not so when powered off. When using only the 536 it will have that 50 ohm load and lower the signal, but it is a $20 dollar solution, compared to $200 that will give a couple of dB in gain.

/Ubbe
 

jonwienke

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When you turn off the 536 it goes high ohm and doesn't load the coax. When it's powered on different switch diodes will conduct and switch in different band filters that loads the signal with different impedancies, not so when powered off.
The 536 only presents a nice 50-ohm antenna load in the band segment it's currently listening to. When off, its Smith chart looks like this:

Smith_536Off.png

When on, it looks like this:
Smith_536On.png

And it changes constantly as the scanner checks different frequencies in different band segments.

A T is a quick and cheap and dirty way to share an antenna, but you're going to have signal loss from splitting the signal and the impedance mismatch at the T, and signal reflections coming from the opposite downstream side of the T are going to affect reception whenever the scanners happen to be scanning different bands. Its only virtue is that it's cheap.
 

Ubbe

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The 536 only presents a nice 50-ohm antenna load in the band segment it's currently listening to. And it changes constantly as the scanner checks different frequencies in different band segments.

....signal reflections coming from the opposite downstream side of the T are going to affect reception whenever the scanners happen to be scanning different bands. Its only virtue is that it's cheap.
Yes, exactly as I explained. So the OP can decide if 3dB higher on the 536's signal meter will be worth the $180. Or he can reach to the back of the 536 and disconnected the coax and move it to the SDS100 and don't loose any 3dB in signal strenght or $180 from his bank account, as he doesn't intend to run the two scanners at the same time.

Maybe a $20 coax cable switch will be more suitable to not suffer from any loss.
Or a $7 one.

/Ubbe
 

megascanner

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Thanks for all the ideas. Really appreciate it. Most of the listening I do is 451.000-480.000 and occasionally air/fire around 153.000-156.000.
 
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krokus

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I just received a PAR VHFBP filter yesterday from Universal Radio. I'm going to play around with it on my dedicated VHF Aircraft scanner (BCT15X). It does more than the typical FM-Notch filter.

View attachment 90275
The Par VHFBP is a special bandpass filter designed for the VHF aero band listener. It passes the VHF civil aeronautical band 116 to 134 MHz and blocks other frequencies. Unlike other aerocom bandpass filters, the VHF-BP not only provides protection from VHF pagers, NOAA, 2 meter amateur signals etc., but also offers excellent attenuation of the FM broadcast band - the primary offender of aerocom signals. BNC female input and BNC male output.

WNIC FM 103.3 out of Dearborn, Michigan hits my home pretty strong. Pager signals are plentiful around me as well.
Did it work out of the box? Do/did you need to adjust any of the trimmers?
 

iMONITOR

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Did it work out of the box? Do/did you need to adjust any of the trimmers?

The adjusters have a little dab of goup to keep them from being moved but it would be very easy to remove it and adjust them. I didn't touch them. Like usual I don't have any good test gear to perform any real meaningful results. However my VHF air traffic appears to have increased substantially and comes in with less noise. Being AM some noise is normal but it seems to have been reduced. I'm going to produce a log and see how it looks. I used to keep the squelch between 3-4 to block noise, now I can keep it at 1 and it only breaks if there is actually a VHF aircraft talking. I'm satisfied.
 
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