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Railfan Technology > What Do I Need for Scanner Receiving Distant Signals


Date: 02/07/20 19:50
What Do I Need for Scanner Receiving Distant Signals
Author: rrman6

Here's my situation.  
The UPRR Golden State Line (ex-Rock Island) in Southwest Kansas with has a crew-change station at Pratt, Ks (35 air miles from me).  This location is near a 45˚ angle southeast of me.  The closest location for receiving the train locos is 30 miles west of Pratt and 23 straight south of me at Greensburg, Ks.  As said, this is the closest proximity for the trains.  When and if I do receive the locos they are distant and hardly understandable. The dispatcher speaking with them is somewhat better, but not the best.  In driving with a mobile scanner between Pratt and Greensburg on a paralleling highway the railroads communicatons are much stronger with my ability to hear.  Naturally being closer to the area I understand the radio signals are possibly transmitted with base directional antennas and the loco radios I assume would be omnidirectional.  What I don't know is that there may be repeater antennas to assist the radio signals along the trackage route.

My radio is an older Bearcat portable TwinTurbo Sportcat.  My antenna is an older Radio Shack omnidirectional with the vertical 16" approx. element and the 3 radial elements located at about 30˚ from horizontal.  This antenna is located atop a 30' steel Rohn tower.  The terrain in all these areas is basically flat so I don't feel anything blocks the signals.  

What might be suggested for better receiving at my home location?  
Would a directional antenna better assist, if there is such available?
I would think the UP antenna's are more directional with the trackage and with possibly some likewise repeaters involved.

Carl



Date: 02/07/20 22:28
Re: What Do I Need for Scanner Receiving Distant Signals
Author: TCnR

Sounds like you have a good antenna set up, it might be worth noting how much feed cable you have and what it's loss would be. That would add loss before the receiver which knocks off the range right away. There may be a way to reduce the cable length or to change to another cable type ( I'm don't have info on cable types and losses, should be available on the www ). One simple change would be to replace the quarter wave whip with a 5/8 wave antenna, sometimes you can find them with the same mount. For any outside antenna be aware of the lightning dangers, there is info on line, there are also local building code and Insurance issues to be aware of.

Looking around the www I was not able to find a spec for that receiver called sensitivity, which could be 0.2 microvolts or lower on a good receiver. Better sensitivity would add to your range.

A well chosen base receiver could help, that would simply be a console type housing of some sort with a built in power supply. If you stay with a hand held style there are HAM radios that could be used, but the rules on these have been becoming more restrictive, there may be something new prohibiting that without a Licence of some sort. Yeasu or Kenwood and a few other manufacturers have been popular in the recent past.

There are directional antenna on the market and those could improve your reception, try searching for the phrase 'Yagi-Uda' which should lead to volumes of info about that type of directional antenna. I've seen them sold on Amazon for this frequency range, also check out HAM Outlet or many other online and actual stores for RF equipment. Any gain antenna may overwhelm a poor receiver causing a number of issues,  the antenna design may need a specific impedance but receivers don't have to be that typically 50 ohm input impedance, that often detunes the antenna or causes problems with the receiver becoming more sensitive to intermods or nearby high powered transmitters, etc.

Another option would be using stacked dipoles, which adds to the range but also adds cables, combining and matching questions as well. I've seen those sold online and also good functional descriptions. The key would be keeping inside the 160/161 MHz band.

Whatever you do, a useful reference is to find your local Weather Broadcast and somehow determine how well you receive it, perhaps by distance or number of different broadcast channels or similar. After you make a change go over to the same Weather broadcast and note that reception has improved or become worse. Tough to do without an actual numerical measurement but it's often a very obvious improvement or worsening.

Quite a while ago I re-cut a Radio Shack FM Band directional antenna to the RR band and obtained a huge improvement in reception, partly because I had it aimed at a high mountain pass. It was very useful but eventually became swamped by local paging services, public services and a nearby Hospital etc.



Date: 02/08/20 06:39
Re: What Do I Need for Scanner Receiving Distant Signals
Author: WW

I'll add to what has been posted already.  First, dump the scanner.  Second, I would recommend buying a good quality commercial mobile radio with an AC power supply,  A number of good analog models are out there, but I would opt for going NXDN digital to have when (at some point) the railroads convert to digital.  My choice for NXDN mobiles would be either the Kenwood NX-700 or the Icom IC-F5061D.  An advantage to either is that they have sufficient channel storage capability (500+ channels) to hold every analog and digital AAR assigned channel.  Both models are commonly available on the used market.  Both radios have excellent sensitivity and selectivity--the latter a feature that most scanners and many amateur radios lack.  To really hear weak distant signals, you need both sensitivity and selectivity.  Both radios require software programming, but once correctly programmed with all AAR channels (with all transmit capability disabled),  plus proper controls to add and delete channels from the scan list,  to initiate or stop scanning, to adjust squelch, and capability to select a single channel when desired, the radio programming should not have to be touched again.

As to the antenna, yes, make sure that you have cable that will minimize signal loss--LMR400 is a very good choice.  Also, make sure that the antenna itself is tuned to around 161 mHz.  In flat country, receiving VHF signals 35 miles away is a pretty long reach.  You will need every advantage that you can get.  If you look, the railroads usually space their remote bases (not repeaters) along their lines in flat country about 10 miles to 25 miles at the maximum apart.  Understand, too, that, in flat country, railroad remote bases are actually "dummied down" in their transmit range so that they do not interfere with remote bases a few miles away along the line.  To illustrate what I mean, when I lived in SE Wyoming, with the best mobile radio and antenna I could barely hear remote bases 20 miles from my location.  By contrast, I could clearly hear the UP's Cheyenne Mountain repeater (a mountaintop repeater) near Colorado Springs, Colorado, 170 air miles from my location.



Edited 1 time(s). Last edit at 02/08/20 06:41 by WW.



Date: 02/08/20 10:46
Re: What Do I Need for Scanner Receiving Distant Signals
Author: 251F

As has been pointed out above, if you have the space for a 5/8 wave antenna, tuned for around 160.800mhz (about the center of the AAR frequency slots) and a good, low loss coaxial cable paired with a good NXDN capable radio will go a long way in improving your RR radio monitoring.

If you're handy with a soldering iron and can attach your own connectors, RF Parts has a decent price/foot of LMR400 low loss cable.
https://www.rfparts.com/lmr400uf.html

For over a decade, I've had a Comet GP-6NC 5/8 wave on the roof.  It is around 10' tall (when assembled), something to keep in mind.  If you live near a Ham Radio Outlet, they generally keep these in stock.
https://www.hamradio.com/detail.cfm?pid=H0-006893

And, as has also been pointed out, don't forget the lightning arrestor.  It does not necessarily take a direct lightning strike to your antenna to cause fatal damage to your radio.

As portables go, I've used an Icom IC-F3161D for nearly a decade.  No complaints except the audio is a bit anemic (tiny speaker) if you use in a moving car.  However, an adapter is available to allow connection of an external speaker which takes care of the problem.  My Icom F3161 is shown with a Laird EXH-160-MXI antenna.  I also have an IC-F5061D in the car.

d.

(disclosure: no, I don't work for any of the afore mentioned companies, yes, I am a ham)




Date: 02/08/20 13:43
Re: What Do I Need for Scanner Receiving Distant Signals
Author: WW

My setups are similar to 251F's.  Icom IC-F3161DT portable, IC-5061DT mobile (both have DTMF keypads because I also used these radios in my employment).  I also used Kenwood NX700 mobile and NX200 portables--again partly due to work I did.  All are very good radios.  In my opinion, the Laird EXH-160 portable antenna is one of the very best portable antennas for railfanning.  Not surprisingly, railroads use tons of them for their portable radios.  By the way, the "MXI" at the end of the Laird model designates the connector on the antenna.  The MXI fits the Icom radio--other radios use different connectors.  As to audio, Icom has essentially replaced the IC-F3161 with the IC-F3261, though the 3161 is still widely available.  The 3261 improves on the 3161 by having louder audio and is rated as waterproof.  A big caveat--the 3261 requires a different programming cable and speaker mike than the 3161.

To expand on the question of the OP on repeaters:  In flat country, railroads most generally use remote bases.  These are usually located trackside, with directional antennas pointed up and down the track.  The remote bases are usually connected to Dispatch centers by fiber, microwave, or IP.  Older remote bases might use code lines, but that is becoming pretty uncommon now.  In hilly or mountanous country, moutaintop repeaters are often used, sometimes as the primary radio communication link, sometimes in combination with remote bases.  They may use UHF or microwave links to interconnect, or may use fiber or IP to connect with Dispatch centers.  In the OP's area, I would be surprised if anything other than remote bases are beling utilized. 



Edited 3 time(s). Last edit at 02/08/20 13:56 by WW.



Date: 02/08/20 14:07
Re: What Do I Need for Scanner Receiving Distant Signals
Author: rrman6

My primary cable is RG50, flexible (stranded copper conductor w/ foam, then braided copper shield) that I used with CB base radio 50 years ago.  Have had the scanner on it for 10 years or more.  This cable length is 30' (antenna to ground), then buried 8" beneath ground for another 15'.  It then enters the house at sub-floor level another 12' to the mid-width center wall where it goes up this wall 4' to an Amphenol male mounted in a wall receptacle cover.  From this point it runs for 3' to the radio through an RG58 flexible coax, solid copper conductor.  All Amphenol connections from antenna to radio are soldered to these silver plated connectors, so although the cable is years old, I hope it to be satisfactory.

I would be interested in learning more concerning good lightning arrestors.  I've never known any of my past antenna's to have been subject of a direct lightning strike, although I've experienced a couple close ones during my 50+ years with this location.  My tower was originally 50' with my Antenna Specialist 3-directional CB base antenna.  After CB outgrew its popularity and as I aged, I no longer wanted to climb and work the taller tower.  About 15 years ago I removed the top 15'.  The only natural growth near this tower is a large catalpa tree with its trunk about 25' away.  No limbs or foliage is near the tower or antenna and the tree trunk is 120˚ left of signal line of sight (Greensburg) or 75˚ (Pratt).  The tower is stationary so am hoping the tree has no affect, however, the city of Lewis, Ks I'm in has 3 to 4 city blocks of normal large tree growth in the signal lines of sight and I have one tall maple tree in my front yard that might affect the Greensburg area.

You fellas have provided me with good information and if there is more to come, it is welcomed.  



Date: 02/08/20 14:56
Re: What Do I Need for Scanner Receiving Distant Signals
Author: rrman6

WW Wrote:
-------------------------------------------------------
> My setups are similar to 251F's.  Icom IC-F3161DT
> portable, IC-5061DT mobile (both have DTMF keypads
> because I also used these radios in my
> employment).  I also used Kenwood NX700 mobile
> and NX200 portables--again partly due to work I
> did.  All are very good radios.  In my opinion,
> the Laird EXH-160 portable antenna is one of the
> very best portable antennas for railfanning.  Not
> surprisingly, railroads use tons of them for their
> portable radios.  By the way, the "MXI" at the
> end of the Laird model designates the connector on
> the antenna.  The MXI fits the Icom radio--other
> radios use different connectors.  As to audio,
> Icom has essentially replaced the IC-F3161 with
> the IC-F3261, though the 3161 is still widely
> available.  The 3261 improves on the 3161 by
> having louder audio and is rated as waterproof. 
> A big caveat--the 3261 requires a different
> programming cable and speaker mike than the 3161.
>
> To expand on the question of the OP on
> repeaters:  In flat country, railroads most
> generally use remote bases.  These are usually
> located trackside, with directional antennas
> pointed up and down the track.  The remote bases
> are usually connected to Dispatch centers by
> fiber, microwave, or IP.  Older remote bases
> might use code lines, but that is becoming pretty
> uncommon now.  In hilly or mountanous country,
> moutaintop repeaters are often used, sometimes as
> the primary radio communication link, sometimes in
> combination with remote bases.  They may use UHF
> or microwave links to interconnect, or may use
> fiber or IP to connect with Dispatch centers.  In
> the OP's area, I would be surprised if anything
> other than remote bases are beling utilized. 

I'd more than likely agree with you on the remote bases.  The Pratt UPRR has a 3-legged free standing tower about 150' southwest of their station.  If I recall correctly,  there are 4 aluminum antennas mounted on the west side, one above the other.  The middle two appear as shorter aluminum elements midway mounted to their horizontal bar mount forming a "T".  The top and bottom of these 4 antennas with longer vertical elements are attached to their two mounts consisting of two horizontal bars w/ one vertical mount coming from the tower.  There may be a shielded rectangular shaped antenna.  This tower may be viewed from 212 Hancock St. on Google Maps.

As westward from Pratt, I don't recall other towers unless they are sitting off railroad property.  I'll have to observe and learn more of what exists in the Greensburg area and eastward. Often times with various communication companies, the rural grain elevators with the top of their headhouse, serve a a mounting and tower, but I don't recall the BNSF or the UPRR in this area using such.



Edited 1 time(s). Last edit at 02/08/20 14:57 by rrman6.



Date: 02/08/20 15:02
Re: What Do I Need for Scanner Receiving Distant Signals
Author: 251F

rrman6 Wrote:
-------------------------------------------------------
> My primary cable is RG50, flexible (stranded
> copper conductor w/ foam, then braided copper
> shield) that I used with CB base radio 50 years
> ago.

If your coax cable is really 50 years old, you may want to consider replacing it.  The "foam" center core tends to shrink and harden with age which has an adverse effect on the signal.

>
> I would be interested in learning more concerning
> good lightning arrestors. 

I'm sure WW can give you even more suggestions, but one of the more cost effective and still possess a replacable gas surge cartridge is Alpha Delta Communication "Transi-Tap" TT3G50.  I just happened to have a spare handly so I could post a picture.  The neat thing about this arrestor is the gas surge cartridge has a "fail safe" failure mode.  That is, if it suffers a catastrophic failure, it shorts.  That's why grounding the arrestor body is so important.  If it ever happens, you can easily unscrew the cartridge and replace it.  Replacement cartridge is around $15.

https://alphadeltaradio.com/pdf/TT3G50_instruction_sheets-6.pdf

Hope this helps.

d.




Date: 02/08/20 15:21
Re: What Do I Need for Scanner Receiving Distant Signals
Author: TCnR

I'm seeing the vertical part of the antennas as the elements, the horizontal part is just a mounting method. The two looped antennas in the middle are identifiable as dipoles that are often used as transmitter antennas. the upper and lower antennas look like 5/8 or maybe just 1/2 wave antennas. All four are simply Omni-directional patterns, often used so that MoW and Supervisors can hear and respond to the Dispatcher. the two plus two pattern could simply be a redundant antenna, or could be a second frequency. My guess is the looped antennas are for Transmit and the two sticks are for receiving, but just a guess. Mobile Land communication is usually vertically polarized.

Most RR antenna installations also have PTC and ATSC antennas on the tower or near the shelter, they often look like large plastic cans that have been sqished at one end, basically a weather proof cover over the antenna.

https://www.google.com/maps/@37.6520415,-98.7405154,3a,60y,239.15h,119.84t/data=!3m6!1e1!3m4!1sqrK8mUfUL_4k_aZRGtMMEg!2e0!7i13312!8i6656



Edited 1 time(s). Last edit at 02/08/20 15:23 by TCnR.



Date: 02/08/20 15:35
Re: What Do I Need for Scanner Receiving Distant Signals
Author: rrman6

251F, this of the suppressor is appreciated much.  
As for this RG50 cable, I have no difficulty receiving Public Service communications from Dodge City (nearly 50 miles), Pratt and Greensburg as well as others within 50 miles northeast.  These are UHF 400>  Mhz signals.  Also receive some various High Band VHF of 15-20 mile radius schools and businesses.  Would this receiving would be such if the cable were at fault as you mention?



Date: 02/08/20 17:50
Re: What Do I Need for Scanner Receiving Distant Signals
Author: rrman6

TCnR Wrote:
-------------------------------------------------------
> I'm seeing the vertical part of the antennas as
> the elements, the horizontal part is just a
> mounting method. The two looped antennas in the
> middle are identifiable as dipoles that are often
> used as transmitter antennas. the upper and lower
> antennas look like 5/8 or maybe just 1/2 wave
> antennas. All four are simply Omni-directional
> patterns, often used so that MoW and Supervisors
> can hear and respond to the Dispatcher. the two
> plus two pattern could simply be a redundant
> antenna, or could be a second frequency. My guess
> is the looped antennas are for Transmit and the
> two sticks are for receiving, but just a guess.
> Mobile Land communication is usually vertically
> polarized.
>
> Most RR antenna installations also have PTC and
> ATSC antennas on the tower or near the shelter,
> they often look like large plastic cans that have
> been sqished at one end, basically a weather proof
> cover over the antenna.
>
> https://www.google.com/maps/@37.6520415,-98.740515
> 4,3a,60y,239.15h,119.84t/data=!3m6!1e1!3m4!1sqrK8m
> UfUL_4k_aZRGtMMEg!2e0!7i13312!8i6656

16 miles west of Pratt is the first siding known as Wellsford siding.  At the east and west switches of this siding are shorter 40' triangular towers with the "can" antennas pointing east towarrd Pratt.  Further west from Wellsford siding is the next siding known as Joy siding, west of Greensburg 5 miles or 35 miles from Pratt.  Here near the top of a tapered metal poles are the simillar "can" antennas near both switches, but "cans" pointing westward.  The pole at the east switch location in addition to the "can" is an antenna element/lightning rod  on top of the pole.  Below the "can" about mid-height on the Joy poles and the Wellsford towers are the two short element antennas like the two middle ones at Pratt, but these appear aimed 90˚ to the track.  Could these be the PTC antennas and the "cans" for train-to-dispatcher/base communications?  Also this trackage is CTC controlled by the dispatcher and I don't know how this is handled by radio.



Date: 02/08/20 18:12
Re: What Do I Need for Scanner Receiving Distant Signals
Author: TCnR

From what I've seen the two middle antennas are for the road channel, I believe the antenna is a ' folded dipole ' but I don't have any references for that.

The cans are probably ATCS, which is like a Command and Telemetry radio signal that replaces the old copper wire code line. The antennas are pointed along the RoW to relay the data to the next trackside installation. When the UPrr  installed the system in Northern California that's the antenna that was used. ATCS can be monitored, pretty big part of the hobby actually. There's a discussion group on Groups.io for it, decoding it requires registration with the group for a number of reasons.

https://groups.io/g/ATCSMonitor

I haven't studied PTS so I can't identify the antennas for it. I believe it's trackside or at the actual g/y/r signal, not sure though. It sure sounds like part of ATCS with some GPS mixed in.



Date: 02/08/20 20:35
Re: What Do I Need for Scanner Receiving Distant Signals
Author: WW

Concerning remote bases along the railroads:  depending on how far they want to reach, a remote base mounted in a signal enclosure with a mobile antenna (such as a Larsen NMO150) mounted on short staff on top of the enclosure may be enough.  I've seen those out on the plains, where the remote bases are separated by 10 miles or so.  Towers can go up in height from there, up to 60' or so, usually.  Railroads don't like to go higher than about 60' with an antenna because taller antennas then fall under FAA regulations for lighting, etc.

On the subject of cabling, I agree with replacing it periodically.  The cable may look fine, but it is often deteriorating inside.  It can also absorb moisture through cable connections.  I've pulled cable connectors apart on  coax and literally had accumulated moisture pour out of the cable. even with the connection sealed with Mastik.

As to grounding for lightning protection, yes--that may still not completely protect the radio, but it may prevent the strike from starting a fire.  It's very important that the antenna grounding be connected (bonded) to the same grounding system that is grounding the power supply for the radio.  If it isn't, then a strike may create a potential between the grounds and fry all kinds of stuff up.  A lot of radio installers miss that one--even some electricians.  With external antennas, even if located in attic, a direct lightning strike--or even one nearby--can cause damage even when proper grounding, surge protection, and lightning arrestors are used.    A lightning strike may be  50,000 volts of current trying to get to electronics designed to run on 12 volts.  Radios that I worked around a lot were in a somewhat lightning-prone area--almost annually we would be replacing antenna cable, a radio, and/or lightning protection someplace in the system (and it wasn't that big of a system)--even with good lightning protection.

Here is a good map of lightning density:  https://www.vaisala.com/sites/default/files/styles/product_main/public/images/PROD-NLDN-2008-2017-flash-density-map-sqm-1280x960.jpg?itok=gDtP-C4y

Where the radios I worked with were located, lightning density was around 3-6 flashes per sq. mile per year.  The OP's Pratt, KS area is about double that.  Need good lightning protection there?  You bet.



Date: 02/08/20 22:08
Re: What Do I Need for Scanner Receiving Distant Signals
Author: 251F

rrman6 Wrote:
-------------------------------------------------------

> As for this RG50 cable, I have no difficulty
> receiving Public Service communications from Dodge
> City (nearly 50 miles), Pratt and Greensburg as
> well as others within 50 miles northeast.  These
> are UHF 400>  Mhz signals.  Also receive some
> various High Band VHF of 15-20 mile radius schools
> and businesses.  Would this receiving would be
> such if the cable were at fault as you mention?

I believe you mean RG-58 cable. 

If your cable has been outside and exposed to the elements, particularly the sun, it will degrade the outer insulation eventually causing very small cracks to form allowing water to enter.  This begins the process of deterioration of the inner "foam" jacket around the center conductor.  Given the age of your cable, the portion that is outside will probably have degraded significantly over the years.  By degrading, it generally translates to more signal loss per foot then when initially installed.

Receiving weak radio signals is all about millivolts (mv=1/1000th [thousandth] of a volt) and microvolts (µv=1/1000000th [millionth] of a volt).  Receiving any radio signal is a fickled thing at best, influenced by many factors including the transmission effective radiated power, antenna (yours and theirs), terrain, weather, solar activity, other transmitters near you that might be desensing your receiver and the list goes on and on.  Because you are receiving some signals and not others, even though some may be closer to you, is not necessarily an accurate gauge as to the health of your coax cable.  The only real way to check that is either measure the VSWR (you would need a transmitter and dummy load) or a cable tester (not a mulitmeter).  All coax cable has some loss.  If you are fighting water ingress causing the inner foam insulation to deteriorate, you will see the loss per foot number increase.

Checking around several websites, a general rule of thumb is, again depending on the cable, 20 years of service outdoors being average.  Newer cable can be found that is UV resistant and would last much longer when exposed to the sun and extremes of temperature.  But given the age of your coax, you stated about 50 years, it's probably a safe bet the outer insulation for the portion of cable exposed to the elements has been comprimised in some manner.

d.



Date: 02/09/20 14:19
Re: What Do I Need for Scanner Receiving Distant Signals
Author: rrman6

251F Wrote:
-------------------------------------------------------
> I believe you mean RG-58 cable. 
> d.

I stand corrected.  Thanks much! 
The primary coax cable from antenna to the last 3' leading to the receiver is RG-8/U  Foam and the last 3' is the RG-58.  
Yes, I agree with you fellas also...it's probably time to replace the RG-8/U with the LMR400 as suggested, as this RG-8/U it is rather stiff and sun affected.  I can't see breaks on the outer cover on what little I examined at ground level, but no doubt with its age and exposure, the minute cracks and aging effect with the inner foam are likely.



Date: 02/10/20 09:56
Re: What Do I Need for Scanner Receiving Distant Signals
Author: Arved

Back when I was younger, before cable TV was popular, it was common for everyone to have a yagi antenna on their roof to pull in TV signals. Since you are looking to get a signal from a specific location, just like we used to do with TV, it makes sense me to that a yagi might be better than an omni-directional antenna for your circumstances. It desn't have to be complicated to build. You shouldn't have a problem finding plans for one - you can adapt plans for 2 meter amature radio to use for RR frequencies.

If you do need omni-directional reception, consider building a J-pole (link). Better than most whips, but not as good as a yagi. Around here, I see the railroads using yagis on signal/relay boxes, although I think the are getting replaced with satalite dishes.

251F Wrote:

> That's why grounding the
> arrestor body is so important.  

It's also a requirement of the National Electric Code. Should you suffer damage due to having an antenna system that doesn't meet code, your insurance claim may be denied. At least if you follow code, and have damage from a lightening strike, you've done due diligence. Getting 100% protection against a lightening strike can be expensive if not impractical, and code minimums do not guarantee immunity from lightening strikes.

ARRL resources on Lightening Protection (link)

Lightning Protection Institute Overview (link).

Better safe than sorry!
 

Arved Grass
Fleming Island, FL
Arved Grass



Date: 02/13/20 12:13
Re: What Do I Need for Scanner Receiving Distant Signals
Author: Rick2582

By all means, use LMR400 or better cable and get a yagi antenna for good reception.  You may need a rotor to swing the yagi to hear traffic from desired locations, espcially if the yagi is high gain.
On a 30 foot tower, you should hear amazing things with this setup.  And i agree, in your area, a lightning arrestor is a necessity.
Good DX (distance) !!



Date: 03/06/20 20:03
Re: What Do I Need for Scanner Receiving Distant Signals
Author: MattW

Something else you could look at is something called an LNA, a filtered LNA is best. It stands for Low Noise Amplifier. I don't use one for voice frequencies as I'm also a ham radio operator, and use a single radio for my railroad listening as well as ham operations, and don't have a way of switching it out when I'm transmitting (on the ham bands only of course). But I do use one for ATCS monitoring and it makes a massive difference in the range of stations I can see. There are several providers, the only one I've used is Uputronics. For ATCS I had to get a custom filtered one, the wideband may work since analog signals aren't as picky as digital, but filtered is definitely better. A quick perusal of their site shows they only have a 162MHz filtered unit which may cover the railroad bands, but a filter more centered would definitely better.



Date: 03/08/20 12:10
Re: What Do I Need for Scanner Receiving Distant Signals
Author: TCnR

Agree with the idea of an LNA near the antenna to compensate for the cable loss. It dawned on me that a large cable loss would suggest an LNA or pre-amp at the antenna, but it's kinda complicated to make it work correctly, not saying it's beyond anybody who's stayed with this post this far. What I've seen on my set ups is that too much gain in the Pre-amp could cause additional problems when the spectrum gets to the actual receiver, problems like broadband noise and intermods from specific Urban sources for example. Being out in the country it may work out ok, but sources like FAA Beacons and Cell Towers can be an issue even out there.

In my line of work I would see the Pre-Amp gain be close to the cable loss, the actual calculations would be beyond what I would try to explain. The most obvious issue is called second stage noise contribution, which in this case is the cable loss, which demonstrates how the noise figure and gain of the Pre-Amp / LNA at the antenna would mask the cable loss. But the down side is the additional broadband noise and spurious caused by the full gain bandwidth of the Pre-Amp / LNA, especially if the receiver has some sort of AGC. Most designs would have filters in the system, but the out of band reflections of the filter would have to be accounted for ( ie: absorbed ). Most designs would also have a more sophisticated Receiver design, an additional downconversion stage for example. There's also what all that additional hardware does to the antenna matching, which often shows up as spurs and intermods that appear out of nowhere, or even generated within the Pre-Amp / LNA itself. That's kinda where the idea of a small amount of gain, offsetting a small amount of loss in the cable comes from. More gain isn't necessarily more range due to other limitations. It would be fun to try it out though.



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