Receiver for high RF environment

[mmori]

Happy Belated Thanksgiving!

I need some help with interference issues while streaming marine radio near an antenna farm. The scanners are picking up strong interference from NOAA weather radio, a ham radio repeater, and possibly a pager transmitter. It seems like intermod is causing trouble.

Right now, I'm using an old Icom IC-M57 marine radio (don't worry, it's in a locked cabinet to avoid accidental transmissions). It's better than a scanner but still has some scratchy noise in the audio. The noise doesn't break the squelch, and it doesn't happen when the radio is receiving a transmission.

The setup is in a room with a furnace and Ethernet gear, using a Tram discone antenna. Since ham and NOAA frequencies are close, I'm not sure if switching to a marine antenna or using a bandpass filter would help. I've also put a 20-pack of ferrite chokes on all the cables I could find.

I'm thinking the noise might be inside the radio, so I'm looking to replace it. The challenge is, new marine radios don't have a 1/8" audio out, and they often need GPS and MMSI. I've checked Icom and Standard Horizon, we're willing to pay for quality.

I'd love to hear if anyone has dealt with a similar issue and what they recommend. I'm open to new or used products—communication receivers, marine or ham radios (preferably with removable microphones), or SDRs. Any suggestions would be helpful.

Thanks!

 

[n1ofj]

Does it sit parked on one channel only?

 

[mmori]

No, it scans a few channels. The noise doesn't break squelch or stop scanning. I forgot to add that the radio is in the same cabinet as the PC, audio is a 1/8" mono cable to a mono-stereo converter and into a USB sound card.

 

[vagrant]

1. An antenna tuned for marine frequencies will be more favorable to that...as well as less favorable to other frequencies you want to avoid.
2. The unwanted RF least resistance is through the discone antenna and your coax vs. into the radio directly, especially if it is in a metal box.
3. Dale Parfitt makes some nice filters you can put inline on your coax that tame NOAA and paging typically around 152 MHz. Still, you should reach out to him and let him know what you want to receive and what you do not. He may have a solution he can tune that will pass what you want. Still, it may not be enough and you may have to add additional filters to reject RFI. PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts

Keep the radio you have and let the filters do the work. You would need the filters with a different radio.
* If you are only monitoring one frequency, a filter tuned to allow mainly that freq would be wise as your first step. As frequencies move further away from that tuned frequency, above and below, they are progressively attenuated/rejected.

I use over 10 of those Par filters due to RFI problems ranging from NOAA, to paging as well as AM and FM broadcast and other nearby strong signals for different systems I use. Hell, I even use additional filters inline with those on some of my stuff, but some are inline on transceivers as well.

 

[prcguy]

1. An antenna tuned for marine frequencies will be more favorable to that...as well as less favorable to other frequencies you want to avoid.
2. The unwanted RF least resistance is through the discone antenna and your coax vs. into the radio directly, especially if it is in a metal box.
3. Dale Parfitt makes some nice filters you can put inline on your coax that tame NOAA and paging typically around 152 MHz. Still, you should reach out to him and let him know what you want to receive and what you do not. He may have a solution he can tune that will pass what you want. Still, it may not be enough and you may have to add additional filters to reject RFI. PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts

Keep the radio you have and let the filters do the work. You would need the filters with a different radio.
* If you are only monitoring one frequency, a filter tuned to allow mainly that freq would be wise as your first step. As frequencies move further away from that tuned frequency, above and below, they are progressively attenuated/rejected.

DCI makes broad band pass filters and they have one for the marine band passing roughly 156.000 to 162.600MHz. I picked one up off eBay cheap and it works very well. I can key up a 50w 2m radio right next to my marine antenna and the marine radio doesn’t know the 2m radio exists.

 

[mmori]

Thanks for the advice! I've contacted the filter manufacturers. I still suspect that there may be an issue with the radio due to old age. If you were setting up a radio to stream marine radio what would you recommend?

 

[Ubbe]

The scanners are picking up strong interference from NOAA weather radio, a ham radio repeater, and possibly a pager transmitter. It seems like intermod is causing trouble.

Right now, I'm using an old Icom IC-M57 marine radio (don't worry, it's in a locked cabinet to avoid accidental transmissions). It's better than a scanner but still has some scratchy noise in the audio.

What scanners is it? Some scanners have better receivers than others. For marine a Pro2006 would work, usually less than $100 in purchase and less than a PAR filter, as that has a very solid receiver that equals a good 2-way radios. Icom can be both a hit or miss when it comes to RF performance.

/Ubbe

 

[prcguy]

Thanks for the advice! I've contacted the filter manufacturers. I still suspect that there may be an issue with the radio due to old age. If you were setting up a radio to stream marine radio what would you recommend?

Do you need all marine channels or just one? If I was setting up for this I would start with the 21ft Shakespeare 476 antenna sitting in my back yard and use either the DCI filter I mentioned earlier for all channel or for just one channel you can use a single 1/4 wave cavity filter which I have a bunch of. Then you could use a cheap SDR receiver or an actual marine radio as the front end filtering will protect from unwanted strong signals.

 

[devicelab]

Dale's VHFSYM162HT saved my primary discone antenna at home due to the NOAA transmission site being LOS on a mountain top. His filter will notch out the Wx quite effectively. It doesn't 'delete' the signal but it does reduce the strength significantly.

 

[prcguy]

Dale's VHFSYM162HT saved my primary discone antenna at home due to the NOAA transmission site being LOS on a mountain top. His filter will notch out the Wx quite effectively. It doesn't 'delete' the signal but it does reduce the strength significantly.

A single 6" notch cavity will have less notch depth, about 20dB max but it will have less than .5dB insertion loss at +/- 750KHz either side of center and about .2dB loss everywhere else giving much more useable reception range. A 20dB reduction of your interfering signal will usually fix most problems. Used VHF cavity notch filters run about $75 and I've got them for much less.

 

[vagrant]

I suggested a solution from Dale as he would dial it in making it ready to deploy upon receipt. DCI is also a good solution and I use their stuff as well. Overall, many do not have the equipment, experience, nor want to configure a filter. I think it fun myself, but there are depths to the hobby. I also use Dale’s stuff in my vehicle where a typical cavity would be problematic. Dale will also leave a filter unsealed/tunable if you ask him when ordering which I do, but most don’t need that.

While I could use a cavity myself for a stationary APRS system, the OP has not advised yet if their need is for a single frequency. Still, a good thread for whomever stumbles in later as options are good.