Multiple Filters

[737mech]

I have three filters PAR FM / PAR 162/ and LTE filter. (I then go in to an EDA 8 way drop amp +4db) I just got the LTE today. After installing I'm happy to report things got better for me. (Your results may vary) I live near Las Vegas and there is a lot of RF in the area. Never thought LTE would be so noisy for my scanner setup. (DPD Log Periodic on the roof/100 ft belden 9913/ PAR VHF SYM 162/ PAR FM/ LTE/ EDA 8 way/ scanners) For $10 bucks worth a try. Not sure if it hurts my mil air band yet. Will find out monday when Nellis AFB starts flying. Just wanted to share the info. I hope somebody else tries the LTE in a city environment inline with the scanner and reports good or bad findings. I would suspect the thing that is happening here is the filters are lowering the noise floor for me and the scanners perform better?

 

[MDScanFan]

What are you listening to that got better after adding the LTE filter to the FM and 162 filters? I currently use the same PAR filters in line for some VHF listening.

 

[737mech]

I listen to VHF air/ UHF air/ 400 ham/ 400 DMR/ 800 P25 / 850 EDACS. The better was in the VHF 154-174 areas and the VHF Aircraft band. For example before I was having trouble hearing KLAS Ground or Ramp control and I don't live too far from it. Lake Meade Park Rangers have a repeater on Mt Wilson at 170.05 that got better. I heard 156.8 marine band also, rare for me. The real test will be this week when the military goes back up. Surprised the LTE didn't kill off my 800 systems? They are very strong here.

 

[MDScanFan]

Interesting. Do you think the signals were impacting the active splitter or the scanners? Did you try if after the splitter for a test case?

I may have to give one of those a try on my discone to see if it makes a difference.

 

[737mech]

The best advise from many here (Prcguy) was to filter before any preamp. I stick to that. Trying anything that cheap won't hurt. Lets face it the networks and cell towers are popping up everywhere. Who knew they might be blasting out our scanners?

 

[spanky15805]

Have you taken into account the 5G band covers the range of 617 - 698 MHz. It's a paired band, so 617 - 652 MHz is for towers to transmit to mobile devices (downlink), while 663 - 698 MHz is for mobile devices to transmit to towers (uplink) from phonescoop. With 5G going up on every other light pole, things are going to get real ugly, rf wise in the next couple of years. Really need to stick an analyzer on there to "see" what's out there. Dosen't help when the chicken banders are dead keying a kilowatt either...

 

[vagrant]

Which LTE filter are you using?

For kicks I just tested using a Channel Master LTE filter with an SDR and an ST2 antenna. I noticed negligible difference on some VHF and UHF ATIS frequencies. I swept the Channel Master and it does filter correctly. I connected the Channel master before and after the other PAR filters I have inline. No big difference with or without it to the different ATIS signal strength and audio quality.

I then dialed up the SDR to the middle of an 800 MHz cellular frequency inside a nice fat cellular signal. The best results with the filter was with placement right at the SDR, as the 91.4 cm patch cable was picking up the 34.1 cm (870 MHz) signal.
-75 dBm - No LTE filter (My normal setup)
-100 dBm - LTE filter inline before drop amp
-106.6 dBm - 91.4 cm patch cable connected to SDR (No antenna or filter connected)
-120.6 dBm - LTE filter connected at SDR with patch cable to drop amp, antenna, etc.
-122.8 dBm - LTE filter connected at SDR with patch cable only...which isn't an option really without a proper antenna connected.

My results do not negate those of 737mech. My RF environment, equipment and setup are not the same. I have two nearby cellular towers. One is about 600 feet away. Another is 125 feet away and the antennas are about 110 feet AGL. My antenna is 30 feet AGL. My results are what I figured they would be.

 

[MDScanFan]

I guess what I was trying to get at is whether or not the issue is overload of the active splitter or the scanners. Have you tried a test case where you disconnect the active splitter and run directly to a single scanner. If the issue stems from the EDA then a more robust LNA (ex 103+) followed by a passive splitter may be worth a try.

I did a quick search and could not many specs for the electro line amps. The price is right though.

The best advise from many here (Prcguy) was to filter before any preamp. I stick to that. Trying anything that cheap won't hurt. Lets face it the networks and cell towers are popping up everywhere. Who knew they might be blasting out our scanners?

 

[737mech]

Thanks I’ll give that a try.

 

[ChrisABQ]

FWIW, I got 2 LTE filters, one for my roof mounted scanner antenna and the other for HDTV. Filters work great. I live in an urban area with 3 cell towers within 600 feet or so, one is about 150 feet away. HDTV interference cleared up nicely. Rooftop antenna is used for VHF and UHF, mostly listen to remote areas in NM. It really cleaned up the radio garbage. Filters 600 mhz and up to include the new 5G band. Been chasing radio ghosts for years. For $25, they have been extremely worthwhile. 700/800 is not a problem as back of set antennas work great on local P25 towers.

 

[737mech]

Posting a follow up I'm really happy I added the LTE filter (Amazon) to my setup. I noticed improvement airband VHF and today the mil 220-400 UHF was great!

 

[Ubbe]

Posting a follow up I'm really happy I added the LTE filter (Amazon) to my setup. I noticed improvement airband VHF and today the mil 220-400 UHF was great!

That's often the case when using TV amplifiers that they sometimes aren't up to the task in high RF signal enviroments. The only specs for your drop amp are 3dB noise figure and no data for IP3 or compression point that tells how much signal strenght it can take before it overloads and degrade in sensitivity.

It migh be that you can get rid of some or all of the filters if you use an amplifier that can handle the high signal strenghts in your location. You have already spent the money for all those filters but a low noise amp at 0,5dB and ip3 of +45dBm could probably improve overall reception. A P103+ based amplifer are $30 and a 1-8 splitter $10. If you put that amplifer at the antenna you will also ignore any coax and connector losses and could probably have some or all filters after the preamp to improve reception even further, if you are looking at doing weak signal monitoring.

/Ubbe