WS 1080 And FM Trap

[scannerjunkie]

I have a friend who is getting the ws1080 for christmas and i cant remember where i read about using an fm trap to help eliminate simulcast distortion. He had the uniden 436hp and sold it due to this issue. i brought my pro 668 to his house and noticed some distortion but he said that my 668 worked better there than the 436hp did. questions i have are 1 do these fm traps really work? 2 where can i get a good deal on one and 3 will it do any harm to the scanner? i want to make sure this is worth buying for him as a christmas gift. any info would be great. thanks. god bless and merry christmas to all.

 

[ridgescan]

If your interest is in airband then yes, the trap works very well. In my case airband was totally deaf NOTHING heard till I got the trap. Now I get stuff.
http://forums.radioreference.com/splitters-filters-multicouplers/233023-fm-trap-airband.html

 

[SCPD]

If your interest is in airband then yes, the trap works very well. In my case airband was totally deaf NOTHING heard till I got the trap. Now I get stuff.
http://forums.radioreference.com/splitters-filters-multicouplers/233023-fm-trap-airband.html

These filters actually will likely attenuate a bit of the air band as well as FM broadcast stations.

However .. most likely your scanner will benefit from getting rid of those FM stations and you will get more transmissions.

Would I recommend buying one .. absolutely YES, cause getting rid of those signals will likely benefit your scanner over all .. particularly on VHF.

But just know that you may get around 3 dB of attenuation in some of the air band .. but really that is like half a bar on your scanner.

Helping simulcast distortion ... doubtful. I don't see it.

Happy Scanning .. :wink::wink:

 

[Mikejo]

I hope this is a good place to ask this question, I would like to build my own "FM trap". I'm wondering if an "R/C-network" high pass filter would work? The type I'm talking about is just a capacitor and resistor combination to attenuate the FM broadcast range.

I'm not sure whether this type of high pass filter will work with radio signals, the other type would be involving inductors and resistors which I am not willing to build at this point.

If the resister/capacitor RC network would do the job, could somebody with experience in this area let me know ?

 

[dlwtrunked]

These filters actually will likely attenuate a bit of the air band as well as FM broadcast stations.

However .. most likely your scanner will benefit from getting rid of those FM stations and you will get more transmissions.

Would I recommend buying one .. absolutely YES, cause getting rid of those signals will likely benefit your scanner over all .. particularly on VHF.

But just know that you may get around 3 dB of attenuation in some of the air band .. but really that is like half a bar on your scanner.

Helping simulcast distortion ... doubtful. I don't see it.

Happy Scanning .. :wink::wink:

Good ones do not have impact on part of the air band that count (generally one only cares about above 118 MHz unless one is withing range of a VOR with voice and sometimes listens to the rare voice there). I use the very good Digikey ZBSF-95-N+ ones in series as I have an FM broadcaster 0.8 miles away. The loss at 119 MHz is about 1 dB (insignifcant); yet they attenuate 88-108 MHz by more than 50 dB. Yes, those filters are not cheap ($100 each) and one normally probably only needs one or could use cheaper ones. (One should try a cheaper one before spending for an expensive one to see if a filter helps and also if a more expensive one might be justified.)

 

[dlwtrunked]

I hope this is a good place to ask this question, I would like to build my own "FM trap". I'm wondering if an "R/C-network" high pass filter would work? The type I'm talking about is just a capacitor and resistor combination to attenuate the FM broadcast range.

I'm not sure whether this type of high pass filter will work with radio signals, the other type would be involving inductors and resistors which I am not willing to build at this point.

If the resister/capacitor RC network would do the job, could somebody with experience in this area let me know ?

I ran through some values and it is not practical which is certainly why no body does that.

 

[Mikejo]

Thanks dlwrunked, I guess an LC network is what I'll have to build.

 

[iMONITOR]

1 do these fm traps really work? 2 where can i get a good deal on one and 3 will it do any harm to the scanner?

1: While FM traps do help to eliminate interference in some circumstances, they will do nothing to eliminate simulcast distortion.

2: Best deals I see are typically on Ebay.

3: It will not harm the scanner in anyway.

 

[devicelab]

These filters actually will likely attenuate a bit of the air band as well as FM broadcast stations.

The airband model from GPIO doesn't...

https://www.ebay.com/itm/FM-Notch-F...ication-Excellent-Rejection-75dB/282762944145

I have his non-airband model and it works really well -- better than the RTL SDR version. I just wish I had a tiny metal case to fit it in... Might try to find an old metal fountain pen body...

 

[Mikejo]

Since I may have to build my own LC network high pass filter, what I am wondering is, are the " choke" type in inductors (you know, the ones that look like resistors but are green), OK to use instead of air Core inductors?

 

[Mikejo]

The FM Trap I'm considering building:

"http://lna4all.blogspot.com/2015/10/diy-fm-trap-or-88-108-mhz-band-stop.html"

Shows air core inductors, what I am wondering is, can one use the "Choke" style inductors as a substitute? (They look like resistors, and are a light green color with bands like resistors)

I have a store near me that has these and I would like to use them if at all feasible.

I will wind my own if I have to, but if anyone with expertise (dwltrunked perhaps?) could let me know, I would greatly appreciate it.

Thanx in advance!

 

[devicelab]

The FM Trap I'm considering building: LNA for all: DIY "FM TRAP" or 88-108 MHz Band STOP filter

Just FYI that filter will cut off the lower portion of the airband. It'll start around 125 Mhz. You'll lose one or two s-units of signal below 125 Mhz.

 

[Mikejo]

Just FYI that filter will cut off the lower portion of the airband. It'll start around 125 Mhz. You'll lose one or two s-units of signal below 125 Mhz.

I'm not worried about that, I'm actually interested in the 160 MHz range, I have a PSR-800 and the front end for VHF is crap.

I just need to know if those choke type inductors will work the same as air core inductors for this FM Trap design.

 

[Ubbe]

You'll need a spectrum analyser to be able to tune the filter properly and it would still attenuate 10dB at 119MHz in the airband. It's a total waste of time trying to build one yourself. Buy that RTL-SDR FM filter, it only attenuates 1dB in the airband and are affordable and in a well screened box.

/Ubbe

 

[Mikejo]

Yup! I was thinking the same thing, looks like it's going to be more trouble than it's worth. I'll probably just buy one. Thanks for the replies!

 

[buddrousa]

If your friend sold a 436 because of simulcast then the 1080 will not last long with him either.

 

[dlwtrunked]

You'll need a spectrum analyser to be able to tune the filter properly and it would still attenuate 10dB at 119MHz in the airband. It's a total waste of time trying to build one yourself. Buy that RTL-SDR FM filter, it only attenuates 1dB in the airband and are affordable and in a well screened box.

/Ubbe

In the plots I just looked at, the RTL-SDR one has a loss at 118 MHz looks more like 6 not 1 dB. The Mini-Circuits one is 1 dB or so at 118 MHz but 5 times the cost of the RTL-SDR. that being said, I have both, the Mini-Circuits one is too big for an HT and I do agree that buying a cheap one and seeing if that is good enough before spending for an expensive better one.

 

[k7ng]

You'll need a spectrum analyser to be able to tune the filter properly and it would still attenuate 10dB at 119MHz in the airband. It's a total waste of time trying to build one yourself. Buy that RTL-SDR FM filter, it only attenuates 1dB in the airband and are affordable and in a well screened box.

/Ubbe

Oh, maybe not a total waste of time. I made a pretty good one for myself.

To whomever cares: I found the FM bandstop filter helps reception about anywhere in the VHF range if the signal environment is strong.
I found some FM 'traps' that are adjustable and are intended to 'notch' a single station whereas a bandstop filter is supposed to take the whole band out. I do listen to airband and I don't think I ever could tell if there was any adverse effect on the signals there.

Regardless of what you're receiving on, the FM bandstop is not a bad investment.