Seeking Feedback on Rail Band Reception Improvement Options

MDScanFan

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I am seeking suggestions to improve my rail band setup. Overall I am pleased with reception but it would be nice to clean up some of the lower level signals. I am limited to attic mounted antennas and a ~75’ min cable run. Right now I am running:
  • Tram 1410 attic mounted - estimate 1.4 dBi gain for the tram at 160 MHz based on my cad model
  • Commscope RG6 at 75’ - around 2 dB insertion loss per supplier datasheet.
  • Kenwood TM-281 - recent edition to my setup. Significant improvement vs my scanners. Thanks to RR forum for the suggestion.
Options I see:
  1. Smaller collinear antenna, such as Laird FM1560 or DPD Traintenna. Laird lists the antenna as 2.1 dBi. Does not seem worth it vs the discone.
  2. A taller collinear. Laird offers a ~ 5 dBi version but at 107” it would only fit in my attic at a slight angle. I need to do the math but it would likely be 25 degrees from vertical. Such an angle would account for around 1 dB polarization mismatch loss along some portions alongside the horizon.
  3. Better coax, such as LMR400. That would give me 1.3 dB loss. Not a significant improvement vs my current coax. And running new thick coax is a pain and undesirable.
  4. Add a preamp at the discone. Potential to buy back the 2dB or coax loss. However, with the discone I would likely need to add both an fm filter and a pager band filter before the preamp - maybe adds 1-1.5 dB rolled up loss before the preamp. Even with a narrow band antenna I may still need both of these.
I am leaning toward 2 or maybe 4 for the best dB band for the buck. Please let me know what you think. I would like to stay under $150 for this improvement attempt. Thanks.
 

AK9R

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Commscope RG6 at 75’ - around 2 dB insertion loss per supplier datasheet.
Does that include losses due to the impedance mis-match between antenna and coax and between coax and radio? RG6 is 75 ohm coax. Your antenna and radio were designed for a 50 ohm transmission line.

If it were me, I'd go with an antenna with a narrower bandwidth tuned for the specific frequency range of interest and 50 ohm low-loss coax.

I would not consider a pre-amp until I optimized every other aspect of the antenna and feedline system.
 

prcguy

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Can you put an antenna outside? The antenna and height are the major contributors to distant reception, so go big, go high. Feedline loss can eat up some of your signal so keep that in check and upgrade if needed.
 

MDScanFan

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After my initial post I measured my attic and I have enough space to fit the 5 dBi Laird. I placed the order and should get it next week. The narrow band and higher gain should help compared to my current discone.

I did not account for the 75 Ohm coax in my numbers above. I figure it may account for 0.5 -0.8 dB of loss max. If I trim my cable to the roughly the right length then I should be able to get the mismatch to cancel at the rail band and negate that impedance mismatch loss. I have not done this yet.

A recurring theme in my threads are (reasonable) suggestions from others to try lower loss 50 Ohm coax. In the near future I may bite the bullet on this and get at least one low loss run of 50 Ohm coax up there. I can then use that to test its impact on the separate setups I am crafting (marine, rail, air, broadband, etc.).

Does that include losses due to the impedance mis-match between antenna and coax and between coax and radio? RG6 is 75 ohm coax. Your antenna and radio were designed for a 50 ohm transmission line.

If it were me, I'd go with an antenna with a narrower bandwidth tuned for the specific frequency range of interest and 50 ohm low-loss coax.

I would not consider a pre-amp until I optimized every other aspect of the antenna and feedline system.
 

MDScanFan

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If I mount it outside, then it would have to go into a tree. And I am not sure I could get it that much higher than the peak of my roof. Plus, the cable run would also increase. Right now it is a 75 foot run to the attic. I estimate 125 to get it to the base of the tree and then an added foot of cable for every foot of height. So it may double may coax run to get it into the tree. One benefit is it is easier to run a thicker coax to a tree than it is to get it into the attic.

I will give this some more thought after I have try the new antenna.

Can you put an antenna outside? The antenna and height are the major contributors to distant reception, so go big, go high. Feedline loss can eat up some of your signal so keep that in check and upgrade if needed.
 

MDScanFan

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Once I get my new antenna next week I plan to try it with and without a preamp in line. If I go the preamp route then I don’t think the type of coax makes much of a difference - the preamp can make up the losses.

In another thread about the marine band I talked about a super strong 155 MHz and some strong pager band signals in my area. I expect those to plague the preamp. I am investigating some notch filters from PAR to help. Are there any bandpass filters specific to the rail band?
 

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Are there any bandpass filters specific to the rail band?
The two preselector filters most serious railroad monitors use are the industry standard ones made by PolyPhaser and Sti-Co. There's usually one available on eBay. Once in a while one of the Sinclair models pops up. Any of the three are solid, and all have about the same insertion loss. Also don't make the obvious mistake a lot of railfans make of putting the preamp before the filter. What's the point in amplifying all the interference? This is the basics of the setup in my personal mobile:

Untitled.png
 
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MDScanFan

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Those are new ones to me. I will look into their specs. Thanks.

The two preselector filters most serious railroad monitors use are the industry standard ones made by PolyPhaser and Sti-Co. There's usually one available on eBay. Once in a while one of the Sinclair models pops up. Any of the three are solid, and all have about the same insertion loss. Also don't make the obvious mistake a lot of railfans make of putting the preamp before the filter. What's the point in amplifying all the interference? This is the basics of the setup in my personal mobile:

View attachment 89552
 

RRR

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We have preselector (Sti-co) filters in our vehicles (Railroad) and they work. Only bad thing is, their range is wide enough to readily allow NOAA weather freqs in. Otherwise, they work great.
 

RadioDitch

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We have bandpass filters in our vehicles (Railroad) and they work. Only bad thing is, their range is wide enough to readily allow NOAA weather freqs in. Otherwise, they work great.
I've never had an issue with the PolyPhaser or Sti-Co filters allowing NOAA to cause interference, though it will allow it to pass so it can be monitored. But interference or bleed over has never been an issue for me personally.
 

RRR

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Yep, be within a few miles of a transmitter, and they sure can, and do. I hear this this nearly everyday.
 

RadioDitch

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Yep, be within a few miles of a transmitter, and they sure can, and do. I hear this this nearly everyday.
Don't doubt it with your installs, however I'm just relating my experience has been the opposite, even if I was nearly directly under it.
 

RRR

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It's usually certain frequencies that do it.

And there are RR comms just above the standard AAR plan that are being used as well
 

JoshuaHufford

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Can you mount the antenna on your roof? Just getting it out of the attic will make some improvement.

If you can stand to be in your attic for a while this time of year can you take your radio up to your antenna with a short coax jumper to see how reception is? That will give you an idea if better coax will be a worthwhile improvement.
 

MDScanFan

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Mounting on the roof is not an option unfortunately. I previously tried a short jumper tests in my attic with my marine yagi. I believe I saw some improvement but it was somewhat hard to tell.

I expect to get my Laird omni later this week. I plan to temporarily mount it to a tree for some easier (less hot) initial configuration testing. It is TBD how high I can get it but maybe 15-20’ above the ground. This is lower than the peak of the roof. I plan to try the following

- Short run of coax
- Fed with ~100’ of RG6
- Fed with ~100’ of DX400
- With FM filter & preamp

Finding a consistent signal will be one of the challenges. I plan to use a dispatch channel that has a lot of traffic and maybe some weaker NOAA signals.

Can you mount the antenna on your roof? Just getting it out of the attic will make some improvement.

If you can stand to be in your attic for a while this time of year can you take your radio up to your antenna with a short coax jumper to see how reception is? That will give you an idea if better coax will be a worthwhile improvement.
 

radio3353

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...I plan to temporarily mount it to a tree for some easier (less hot) initial configuration testing. It is TBD how high I can get it but maybe 15-20’ above the ground. ..
Will the antenna be clear of the tree? Leaves have an attenuating effect on radio signals. Don't forget lightning protection.
 

MDScanFan

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The antenna will not be in the clear. It will be mounted around 15-20’ off a large lower branch on a very tall tree. It is for a temporary installation to run some tests and it is the best I can do aside from inside my attic. Ultimately this antenna will likely make its way into the attic in the end.

Will the antenna be clear of the tree? Leaves have an attenuating effect on radio signals. Don't forget lightning protection.
 
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