Jim 96XI-1 Adjustable Notch Filter--1st Impression

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emscapt9816

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Hello all. Well, I just got home and found my UPS box from Scanner Master waiting for me. I wanted to take a moment to share my first impression with my new notch filter. First, the cons. There are no mounting tabs on the case in order to mount it to a rack with screws, it only comes with 4 adhesive pads on the back. Second, and most annoying, the front of the filter, which in the website photo shows what looks like a rotary indicator, is actually a STICKER! A STICKER! Here I am thinking I would actually be able to see where I was tuning this thing. However, the pros, IMHO, outway the cons. First, it is a solid piece, made from die cast aluminum. Second, it is variable. Using my PRO-500 with the Win500 Monitor/Control, I was able to tune the filter to eliminate overload interference from a local FM station blasting away my VHF-Hi reception. Third, and most importantly, IT WORKS! I am receiving better on ALL bands, not just the VHF-Hi. I welcome comments and questions. I hope my little review is informative.
 

0077

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filter

Could you tell me how you adjust the filter? What is the setting you use?
And where would I find it?

many thanks...
 

emscapt9816

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Could you tell me how you adjust the filter? What is the setting you use?
And where would I find it?

many thanks...
I purchased the filter from Scanner Master http://www.scannermaster.com/Jim_96XI_1_Adjustable_Notch_Filter_p/36-531260.htm . The filter is adjusted using a tuning knob on the bottom. I can't tell you what setting I used, because it's a sticker on the front. :( I adjusted the filter by monitoring the PSR-500 through the Monitor/Control window in Don Starr's Win500 program. I selected an inactive VHF-Hi frequency on the radio (5 bars on the S-meter) and slowly turned the knob until the the S-meter dropped to zero, while monitoring the numerical signal meter box in the Win500 window, dropping from the 600's in strength, to between 200-300's in strength. Once set, I am now receiving VHF-Hi frequencies previously missed.
 
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Hello all. Well, I just got home and found my UPS box from Scanner Master waiting for me. I wanted to take a moment to share my first impression with my new notch filter. First, the cons. There are no mounting tabs on the case in order to mount it to a rack with screws, it only comes with 4 adhesive pads on the back. Second, and most annoying, the front of the filter, which in the website photo shows what looks like a rotary indicator, is actually a STICKER! A STICKER! Here I am thinking I would actually be able to see where I was tuning this thing. However, the pros, IMHO, outway the cons. First, it is a solid piece, made from die cast aluminum. Second, it is variable. Using my PRO-500 with the Win500 Monitor/Control, I was able to tune the filter to eliminate overload interference from a local FM station blasting away my VHF-Hi reception. Third, and most importantly, IT WORKS! I am receiving better on ALL bands, not just the VHF-Hi. I welcome comments and questions. I hope my little review is informative.
Sticker, really? I don't know about all that noise. If I'm going to pay 80 bucks for a hunk of cast aluminum with a sticker on the front it better work damn good. I'm assuming that the adjust on the bottom of the unit at least corresponds with the frequency range of the sticker. I WAS going to purchase this filter for my handhold's/bases, however now I think I will go with something of quality.

lol...sticker
 

emscapt9816

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"Sticker" Shock

Sticker, really? I don't know about all that noise. If I'm going to pay 80 bucks for a hunk of cast aluminum with a sticker on the front it better work damn good. I'm assuming that the adjust on the bottom of the unit at least corresponds with the frequency range of the sticker. I WAS going to purchase this filter for my handhold's/bases, however now I think I will go with something of quality.

lol...sticker
The knob does kinda correspond with the sticker, but like I said, it WORKS. I've had it 24 hours now. I can't believe the stuff I was missing. (Well, I can.) I bought it specifically because it's adjustable. Aside from the sticker, I'm quite happy with it. The manufacturer could have deleted the sticker altogether, the knob will still work.
 

hoser147

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Glad its working for you Eric, It kinda burns ya when the pic implies its one way and you get it and its different. I didnt know anyone used 2 sided tape anymore thought it was velco now days. The Sticker Shock was good......... Hoser
 

thewenk

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I think the adjustable notch filter is a great item and obviously worked very well in this case.

A much cheaper ($14 + shipping) item, is the Winegard FM 7500 FM trap which attenuates the entire FM band.

I had looked at the adjustable filter previously, but decided to go with the cheaper item first. The Winegard filter has solved 99% of my interference problems. It may not solve severe problems, but it is something to consider, and a lot cheaper.
http://www.solidsignal.com/prod_display.asp?PROD=FT7500

Dave
 

emscapt9816

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i was initially looking for an FM trap. Radio Shack used to sell one years ago. If I remember correctly, the attenuation was about -15 dB. The attenuator on the scanner is -20 dB. The notch filter attenuates a minimum of -30 dB, and like I said, it eliminated the interference from a very close transmitter putting out something like 3000 watts (it serves all of Long Island). I initially was going to purchase a Par VHF-FM filter. Dale was very helpful answering my questions, and his filters have received rave reviews. It was the adjustability of the Jim filter that sold me.
 

K2QI

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Sorry to drag up an old thread, but was hoping the OP could help. Just got this filter with hopes of solving my airband interference problems, and yet this filter doesn't seem to do anything.

Turning the knob back and forth on an unused VHF hi frequency with 5 bars does nothing; the signal meter still stays pegged and the numerical signal box stays in the 600's. In fact, order to get anything with this box, I still have to use an AOR bandpass inline with the antenna. I'm sorely disappointed.
 

tilleyhat

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...and yet this filter doesn't seem to do anything.
Turning the knob back and forth on an unused VHF hi frequency with 5 bars does nothing...
- I bought this filter for 29$+shipping in internet. It works well. What i do to check to see if the filter works well: I tune the highgest FM's station close to 108mhz (in my case 107.3 fm music station) in the scanner, i hear clearly the music playing, then i turn slowly the knob until it completely cuts out the music. I make a pen marking right toward the white line on the knob. this is my 88-108 cut-off point.
 

Mike_G_D

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tunable notch filter

amstel78,

I know from reading multiple threads of yours that you are very frustrated and I don't blame you. You have obviously spent some considerable time and money trying to solve your problem (apparent overload on the civil aircraft band). Unfortunately, this may not be an easy fix in your case simply because of where you live. It could be that you are getting hammered by multiple sources and if so, one narrowband notch may not be sufficient. If the interferers are reasonably close in frequency (say both are FM broadcasters) then a broader band notch filter may be the solution. There are FM trap filters designed to notch out the whole FM broadcast band and these may be a good choice IF that is the problem.

But, I think, if I were you, before I'd go any further and spend any more money I would try and do a little more investigating. We really need to find the REAL source of your problem. I would first try and use a cheap FM radio and see if I could locate exactly which station is causing the problem or which stations plural, if applicable.

Firstly, a tunable notch filter should be adjusted very slowly. A quick sweep of the dial may easily miss the mark and you may not even notice it. If you have a rough idea what station it is and where on the FM dial it is then you should start by tuning the dial on the notch filter to that general area (I know the frequency indications are very rough on the filter but we're just getting in the ballpark). Then, very slowly, while listening to and interfered with frequency, tune the dial on the notch filter around and listen carefully - it will likely be a very sharp change at some very specific point on the dial which, if you move past will sound like a quick spurt of change followed by the interference again. A good narrowband notch filter will have a deep notch at the tuned in frequency with steep skirts to the sides so as to focus the notch effectively while passing surrounding frequencies. This is why you may have missed it if you tuned it too quickly. Again - if we can locate the exact culprit first then we know where to focus our efforts.

If it turns out you have multiple culprits then you may have to play around to find the worst of the bunch and settle for that or get a broadband trap if the frequencies of the interferers are not too far apart.

It is also possible that you are so close to the interferer(s) source that no filter will attenuate enough to help you - in that case your only option would be to change location, at least when monitoring the aircraft band. It is also possible that the scanner could be getting leakage through its internal circuitry - after the antenna port. If you are getting an extremely strong interferer signal this is possible - again, about your only option here is a change in location (unless you want to build an RF shield around your scanner).

I still think you should first stop, take a deep breath, and then focus your efforts into finding exactly what the interferer is and where, in frequency, it is (or they are, if multiples). If you want, I will be happy to guide you further via PM. But, again, this is where I would start.

-Mike
 

Mike_G_D

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notch filter

tilleyhat,

I forgot to mention that the scanner that amstel78 is using cannot tune the FM broadcast band so your method, while valid for scanners that have that band, could not work in this case. This is why I suggested using a cheap FM radio to find the interferer.

-MIke
 

Mike_G_D

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notch filter

amstel78,

...and of course, I JUST now saw your post in the NY forum - didn't think to look there first...sorry!

Anyway, since that TV station (WABC) is at least one of the culprits then you made the right choice at least in terms of the notch tuning capability (an FM band specific unit would obviously not work here). Since we know that the frequency is around 180MHz then I would start by tuning the notch filter to the top end of its range (apparently about 190MHz) and slowly adjust back down in the manner I described above. It may be possible that this filter is not effective at this frequency as it is close to its top end of its range. If so, you may have to order a specifically tuned single frequency notch filter for this problem. Again, PM me if you want to and I'll give what advice I can.

-Mike
 

K2QI

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Mike, thanks for your reply.

I think my problem lies with the fact that I live extremely close to hi-wattage transmitters. So powerful in fact that the notch filter cannot attenuate the signal.

For example, let's say I tune to 118.5000. With no filter and an RH77CA antenna, the signal meter is pegged on my 500 and I cannot squelch out the channel unless I turn the scanners built-in attenuator on.

With the notch filter in place, just as a test, I would rotate the knob slowly to where I think 118.5 is. I'd look at the signal meter on my scanner and on the readout displayed in WIN500 while turning the knob. The signal meter may drop one bar, and the readout may drop from 780 to 690. It fluctuates so much that it's hard to get a certain measurement. With the notch filter, in principle I was expecting to attenuate that 118.5 completely. In this case it doesn't happen as was in the OP's example.

Now, I'm left to think that a) there's something wrong with the filter, or b) whatever's blasting 118.5 is so strong that even the filter can't attenuate the source. So, I tried using a different antenna. I switched to the stock duckie that came with the 500. Repeating my test, I was able to attenuate that frequency all-together to the point that the signal meter drops to 0.

So now, where does that leave me? I was expecting to have this notch filter attenuate offending frequencies while using a hot antenna, and it doesn't. In fact, I have to use my AOR bandpass filter in conjunction with the notch filter to get any decent airband reception.

I think I've elliminated birdies from those frequencies as well because I've tested the scanner without an antenna and antenuate off, and I don't get a signal reading.

All I want to know is, is there something wrong with this notch filter? I paid $75 bucks for this thing from Scanner Master, and from what I've experienced, doesn't do what I need it to do.

EDIT: I take it back.. just tried with the stock duckie and a frequency of 108.0000. I can still hear FM bleed-through, and the notch filter alone isn't getting rid of it. I'm rotating it slowly back and forth throughout the whole range, and nothing. Sometimes the signal strength dips a little and then jumps right back up again.
 
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Mike_G_D

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Notch filter

amstel78,

I think you don't completely understand how to use the notch filter. You should not try and adjust the filter to the frequency you are listening to; you are trying to notch out the INTERFERER and NOT the actual desired signal! So, the idea is to tune the filter to the frequency OF THE INTERFERER while listening to your desired frequency (since you can't tune the FM broadcast band or the TV broadcast bands on your 500). So in this case, let's say you are listening to 118.5MHz. You hear the nasty undesired interference. Then, let's say the problem really is WABC TV at around 180MHz. Then you would slowly tune the notch filter's dial around the approximate area that 180MHz is located (from the previous posts, I know that the sticker is pretty rough but it should give you a ballpark point to start at - it should be near the top end of the notch filter's range since it is spec'ed to go to 190MHz). Tune very slowly and note when the noise on your desired frequency (118.5MHz) "dips" as you say. When you note the change, then, even more slowly, carefully adjust the filter a little back and forth so as to "zero in" to the exact frequency. At some point it will have the best effect, hopefully good enough. But, as you say, if you are so close it might not be enough. Anyway, from your last post, I think you really are confused as to how a notch filter works so you need to rethink it and retry.

-Mike
 
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K2QI

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amstel78,

I think you don't completely understand how to use the notch filter. You should not try and adjust the filter to the frequency you are listening to; you are trying to notch out the INTERFERER and NOT the actual desired signal! So, the idea is to tune the filter to the frequency OF THE INTERFERER while listening to your desired frequency (since you can't tune the FM broadcast band or the TV broadcast bands on your 500). So in this case, let's say you are listening to 118.5MHz. You hear the nasty undesired interference. Then, let's say the problem really is WABC TV at around 180MHz. Then you would slowly tune the notch filter's dial around the approximate area that 180MHz is located (from the previous posts, I know that the sticker is pretty rough but it should give you a ballpark point to start at - it should be near the top end of the notch filter's range since it is spec'ed to go to 190MHz). Tune very slowly and note when the noise on your desired frequency (118.5MHz) "dips" as you say. When you note the change, then, even more slowly, carefully adjust the filter a little back and forth so as to "zero in" to the exact frequency. At some point it will have the best effect, hopefully good enough. But, as you say, if you are so close it might not be enough. Anyway, from your last post, I think you really are confused as to how a notch filter works so you need to rethink it and retry.

-Mike
Hi Mike,

No, I understand the way the notch filter works. However, my test described above was supposed to show that the notch filter didn't even attenuate a specific frequency I chose. If it can't do that, then how am I supposed to know it's doing its job wth frequencies bleeding over?

At 108.000 for example, I was getting a lot of FM radio intermod. I would very slowly sweep the dial through it's range, and it couldn't attenuate the offending frequency when I used an RH77CA antenna. This is why I'm thinking that either the filter doesn't work as advertised, or RF interference is so strong that it's swamping the notch filter by itself, requiring the added use of a bandpass filter.
 

Mike_G_D

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notch filter

amstel78,

I think I can explain - at least some of the apparent "strangeness" you are seeing.

When you tried to "notch out" the interference at 118.5MHz you expected that tuning the filter to 118.5MHz would reduce the level there. As you say, you understand that you should tune the filter to the interferer's frequency but you thought that you could test it by tuning it to any frequency wherein you receive interference and see the level drop. Unfortunately, it will not work that way. The noise/interference you here at 118.5MHz or 108MHz is not really there - it is on some other frequency or number of frequencies. It is "bleeding over" - that is, in this case, appearing on these other frequencies (118.5MHz and 108MHz, to use your examples) because of weaknesses in the receiver's frequency conversion networks when faced with certain high level out-of-band signals. So by tuning the notch filter to your "desired" frequencies (118.5MHz and 108MHz) you will hardly at all affect the apparent level of noise/interference because it isn't really there anyway (but the scanner is being "tricked by brute force" into making it appear there). The only way you can really test the notch filter is to actually try and notch out a real signal that is really on the frequency you want to test it at. I suggest, if you want to try this, to try your local weather frequency at 162.XXX MHz and tune the filter there while you are listening to it and see how much it drops the signal. Any other desired signal, such as a pager signal at 152.XXXMHz or taxi base station or some LMR strong signal that you know belongs on some frequency within the notch filter's tune range (80MHz to 190MHz) would also be a good candidate for testing; I mention the weather frequency because it is continuous and therefor easy to test. If the filter will not work on real known on-channel signals within its specified range then it may, indeed, be defective. If it does work, and despite all your best efforts, cannot reduce or eliminate your problem then it may be that:

1) You have more than two interferers that are causing the problem ("intermod" as described by most scanner users, is usually caused by the interaction of two interferers which internally mix to cause the the result to match the receiver's internal IF; when this happens, you hear a mixture of those two signals being heard all across the band between the two interferer frequencies - if you can notch out one then you should be able to solve the problem. Unfortunately, if there are multiple interferer "pairs" causing such problems then you would need multiple "notches" to cover them all).

2) You have a severe overload situation wherein the interferer is swamping the receiver by either the fundamental or a harmonic of the fundamental simply overwhelming some point in the receiver's frequency conversion chain. Depending on how the signal is really getting into the receiver and how strong it is, it may not be easily dealt with.

3) The interferer's frequency (or frequencies) is/are located outside the range of the notch filter's "notchable" bandwidth.

4) The notch filter is just not attenuating the interferer enough due to your proximity, etc., as we've already discussed.

Or some combination of the above.

There are other avenues of typical receiver interference such as images, 1/2IF, and basic adjacent channel interference. But all those are specific to a desired frequency (only affecting a certain specific frequency) - it sounds like you are getting a "splatter" type interference which covers a large range of frequencies so I think it more likely you are suffering from the possibilities I noted above or some combination thereof (the last two are actually sub-categories of the first two, in a sense).

I honestly wish you luck! And I honestly sympathize! But I would test the notch filter first by trying it on a well known constant (NOAA weather broadcasts) or almost constant (pager, taxi base) signal within the filter's range and see what it does - if it has little or no effect on those then it may indeed be defective.

-Mike
 
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K2QI

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Hi Mike - thanks again for the detailed reply. I will try what you've suggested and see if I can tune out the NOAA station near by. If it can't do that, then I'll send the unit in for replacement/refund. I'll keep you posted.
 

Mike_G_D

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notch filter saga continues

amstel78,

One other thing I think you should try - try sending a PM to the originator of this thread, emscapt9816, and see if you can physically meet with him (I see he is also in New York) - since he has the same setup you do (same scanner and filter) he might be able to help you in testing it and comparing your separate experiences. I think that might help you out a lot. If I were in your situation, having someone locally with the same setup to communicate with would be somewhat desirable! See if you can PM him directly and maybe he can help you out?!

-Mike
 
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