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FM filter for SDS100 RTL-SDR

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Dec 19, 2002
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301
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ON CAN/Hope AR USA
#1
Is anybody using one of these? I’ve read very good reviews on them and figured I would give it a shot for my SDs100. I should have it by Friday.
Mike



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vagrant

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#2
Yes, I am using the RTL-SDR AM band filter as well. I forget the dB numbers, but both filters do what they say and are well worth the price. I believe I purchased a second set after observing the results. Yes, thinking about it further I have two sets in use and I believe I have spare set for handheld/portable gear.
 
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Messages
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#3
Yes, I am using the RTL-SDR AM band filter as well. I forget the dB numbers, but both filters do what they say and are well worth the price. I believe I purchased a second set after observing the results. Yes, thinking about it further I have two sets in use and I believe I have spare set for handheld/portable gear.
For typical scanner use (118-1000mhz) should I also get the AM filter?
Mike


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ka3jjz

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Bowie, Md.
#4
That depends entirely on your local RF environment. Take a look around MW stations in your area and see which ones blow in like a hurricane. Take your antenna off completely and run your scan. These will be your potential problem children.

AM band (better name: MW band) filters are very useful if you are getting a lot of bleed thru where MW stations show up in the HF band (2-30 Mhz) and higher as distorted spurs. The typical RTL stick (without any up-conversion or other tricks like direct sampling) doesn't cover any lower than 25 Mhz. But if you are hearing MW stations where they don't belong - and the typical stick really doesn't have a lot of front end filtering to begin with - then it's worth considering.

Be aware of their pitfalls, however. One easy gotcha is to make sure the filter actually cuts off the MW frequency (or frequencies) that are giving you trouble. Find the filter's response curve, or look at the specs (if they have it). If you are having issues with a station on 800 Khz, for example, and the filter's response doesn't start until 1000 Khz, it won't solve your problem. Now you know why I said to look for MW stations that blow in like a hurricane....Mike
 
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Messages
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Location
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#5
That depends entirely on your local RF environment. Take a look around MW stations in your area and see which ones blow in like a hurricane. These will be your potential problem children.

AM band (better name: MW band) filters are very useful if you are getting a lot of bleed thru where MW stations show up in the HF band (2-30 Mhz) and higher as distorted spurs. The typical RTL stick (without any up-conversion or other tricks like direct sampling) doesn't cover any lower than 25 Mhz. But if you are hearing MW stations where they don't belong - and the typical stick really doesn't have a lot of front end filtering to begin with - then it's worth considering.

Be aware of their pitfalls, however. One easy gotcha is to make sure the filter actually cuts off the MW frequency (or frequencies) that are giving you trouble. Find the filter's response curve, or look at the specs (if they have it). If you are having issues with a station on 800 Khz, for example, and the filter's response doesn't start until 1000 Khz, it won't solve your problem. Now you know why I said to look for MW stations that blow in like a hurricane....Mike
Thank you! I will look into the RTL-STL filter and see if it might be beneficial.

The FM filter will be a good addition to the Slim Jim dual band antenna and the SDS100 scanner. I will research MW harmonics and see if they affect any of the bands I monitor. If so I’ll grab an AM filter as well.

On a side note I wonder how the hardware FM filter will affect the software filters on the SDS100? I may need to post in the Uniden forum later.

Again thank you for the information!
Mike


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ka3jjz

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#6
By the way, the exact same logic can be used for your local FM broadcast stations. And the caveat about watching the frequency coverage is the same as well - just adjust the example I gave for a FM station and the logic still holds true

Mike
 

vagrant

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#9
I have two MW stations and one FM station close by. Filtering out that band really helps at my location. Your RF environment may be the same, better, or worse. For the price these filters work very well. I have paid five times that much for a MW (AM) High Pass Filter that is comparable in performance. I believe the insertion loss is low as well. I will probably purchase more because I have too many receivers. ;)
 

ratboy

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Nov 3, 2004
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803
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Toledo,Ohio
#10
I got one of these;
filter.jpg
and tried it on my SDS200, and wow, it just knocked the whole VHF/UHF and up spectrum down from 7 db to about 11-12.
I hoped it would help, as there is a local FM station that causes hash on some radios, and knocking down HF might help too. It was so bad, I verified how much it affected signal strength by plugging it into a Spectrum Analyzer and then my antenna (Just a whip about 18" long) and the only place it had a 1 db loss was in the very low Aircraft band around 115 MHZ. By 138 MHZ it was down about 8db. At 800 MHZ, it was down 12db. Now I need to find my Par filter I misplaced when I moved, and see what that can do. I know it works as advertised. I think I'm going to open up the HPN-30118 and see if something wasn't soldered inside.
 
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Messages
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Location
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#11
I got one of these;
View attachment 71300
and tried it on my SDS200, and wow, it just knocked the whole VHF/UHF and up spectrum down from 7 db to about 11-12.
I hoped it would help, as there is a local FM station that causes hash on some radios, and knocking down HF might help too. It was so bad, I verified how much it affected signal strength by plugging it into a Spectrum Analyzer and then my antenna (Just a whip about 18" long) and the only place it had a 1 db loss was in the very low Aircraft band around 115 MHZ. By 138 MHZ it was down about 8db. At 800 MHZ, it was down 12db. Now I need to find my Par filter I misplaced when I moved, and see what that can do. I know it works as advertised. I think I'm going to open up the HPN-30118 and see if something wasn't soldered inside.
I was looking at that exact filter! Someone I know said they had one and it attenuated everything. The RTL-SDR filter (so I am told) does not hamper reception out of the FM band. I’ve heard amazing things about Parr filters! I think I might order one of those for my car scanner setup!!
Mike


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ratboy

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Messages
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Toledo,Ohio
#12
The Par/Parr filter worked wonders on a couple of my old scanners. My old Uniden BC9000XLT had major intermod and a general hash without it, and it made it barely tolerable for anything but 800 amalog to pretty decent. The radio had no capture so a lot of the time when skip was happening on VHF and UHF, it just sounded like a mess of grinding signals. All in all, a disappointing scanner. My Pro-2004 (Still working!), and 2005 (Still working) had no worries about being replaced.
 
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Messages
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Location
Stockholm, Sweden
#15
My HPN-30118 filter suddenly went bad after 10 years of use and it depended mostly on how the female BNC connector where pushed to one side. Opened it up and the middle pin had broken loose from the solder to the components. It might be some bad cold solder joints in this filters that needs to be taken care of. The persons soldering the filters might not spent enough time on the solder job, maybe they are paid per filter. My filter measures as good as the one DG8SAQ mesured and are the best of the filters I got.

/DD
 

kruser

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St. Louis County, MO
#16
My HPN-30118 filter suddenly went bad after 10 years of use and it depended mostly on how the female BNC connector where pushed to one side. Opened it up and the middle pin had broken loose from the solder to the components. It might be some bad cold solder joints in this filters that needs to be taken care of. The persons soldering the filters might not spent enough time on the solder job, maybe they are paid per filter. My filter measures as good as the one DG8SAQ mesured and are the best of the filters I got.

/DD
I had one of two HPN-30118 filters fail. It was also a bad solder joint at the female connector inside the little case.
The center pin on the female BNC used was not machined well and had a lot of play. I figured this play eventually broke the solder after who knows how many times I'd inserted and removed the filters.
Once I found that, I replaced the female jacks on both of my filters with quality bnc jacks and they work just fine to this day. Still not quite as well as my PAR FM trap but good enough for most purposes.
 

vagrant

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Joined
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Messages
751
Location
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#18
I have two of the HPN-30118 filters and no problem here. I gave them a good wiggle during testing and no issue. I believe the first one I ordered was in 2012; the second was in 2015. I believe they are made in the Czech Republic. One of them is used on the scanner in the vehicle. I like them for handhelds as they do not add much to the profile.
- From 87 - 108 MHz the drop range was around 25 to 45 dB. (Averaging both)
- From 38 MHz and down it really started to plummet to 70+ dB and more.
- There was about 1 dB of loss elsewhere, so it is a fair compromise for me.

The RTL-SDR FM filtered 46 - 59 dB through 88 - 108 MHz. The loss was around .5 dB elsewhere after 138 MHz. A definite improvement over the HPN-30118. Still, I took a hit on VHF air low though. It went from -15 to -1 dB climbing from 118 - 138 Mhz. At home the RTL-SDR filters are static in placement and an inexpensive solution.
 
Joined
Dec 19, 2002
Messages
301
Location
ON CAN/Hope AR USA
#19
I have two of the HPN-30118 filters and no problem here. I gave them a good wiggle during testing and no issue. I believe the first one I ordered was in 2012; the second was in 2015. I believe they are made in the Czech Republic. One of them is used on the scanner in the vehicle. I like them for handhelds as they do not add much to the profile.
- From 87 - 108 MHz the drop range was around 25 to 45 dB. (Averaging both)
- From 38 MHz and down it really started to plummet to 70+ dB and more.
- There was about 1 dB of loss elsewhere, so it is a fair compromise for me.

The RTL-SDR FM filtered 46 - 59 dB through 88 - 108 MHz. The loss was around .5 dB elsewhere after 138 MHz. A definite improvement over the HPN-30118. Still, I took a hit on VHF air low though. It went from -15 to -1 dB climbing from 118 - 138 Mhz. At home the RTL-SDR filters are static in placement and an inexpensive solution.
I think I’ll get one of these for my car!!
Mike


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kruser

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#20
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