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Railfan Technology > Do I need a new antenna?


Date: 03/27/24 06:11
Do I need a new antenna?
Author: march_hare

I have a Bearcat BC125AT handheld scanner, which rides around on the front seat of my truck. A lot of my railfanning is "targets of opportunity"--if I hear a train nearby and the conditions are favorable, I'll divert from my daily running around and grab a few photos. 

Most of the time, I just set up to scan the entire railroad band, and don't bother programming individual frequencies. 

Lately, I've noticed a sharp decrease in radio intercepts. I'm wondering if my rooftop magnetic antenna (Railcom) is to blame. I run the antenna cord out through the rear door opening on my pickup truck. Consequently, the cord gets squished between the door gasket and the metal door frame whenever I close the door. I'm careful to avoid catching the cord in the latch mechanism, but over the past 4-5 years, the cord has acquired a series of permanent bends where it goes through the door. 

This cord is a coaxial cable, so I'm thinking the shielding layer may have been compromised?  If so, can the cord be replaced, or should I just buy a new antenna?

And is there any way to shield the cord from kinking like this over time?

Thanks for any advice for this (obviously) low-tech user. 



Date: 03/27/24 06:17
Re: Do I need a new antenna?
Author: engineerinvirginia

march_hare Wrote:
-------------------------------------------------------
> I have a Bearcat BC125AT handheld scanner, which
> rides around on the front seat of my truck. A lot
> of my railfanning is "targets of opportunity"--if
> I hear a train nearby and the conditions are
> favorable, I'll divert from my daily running
> around and grab a few photos. 
>
> Most of the time, I just set up to scan the entire
> railroad band, and don't bother programming
> individual frequencies. 
>
> Lately, I've noticed a sharp decrease in radio
> intercepts. I'm wondering if my rooftop magnetic
> antenna (Railcom) is to blame. I run the antenna
> cord out through the rear door opening on my
> pickup truck. Consequently, the cord gets squished
> between the door gasket and the metal door frame
> whenever I close the door. I'm careful to avoid
> catching the cord in the latch mechanism, but over
> the past 4-5 years, the cord has acquired a series
> of permanent bends where it goes through the
> door. 
>
> This cord is a coaxial cable, so I'm thinking the
> shielding layer may have been compromised?  If
> so, can the cord be replaced, or should I just buy
> a new antenna?
>
> And is there any way to shield the cord from
> kinking like this over time?
>
> Thanks for any advice for this (obviously)
> low-tech user. 

I'd say the cable is compromised....if it can be replaced separately, have at it. Otherwise you might have to get the whole thing...



Date: 03/27/24 08:02
Re: Do I need a new antenna?
Author: WW

The cable shielding is critical for the antenna to perform correctly and can be easily compromised by hard bending or crushing.  Also, you might check where the cable is physically connected to the BNC connector.  Constant connnecting and disconnecting of the connector from the radio can physically compromise the shiedling connection to the BNC connector.   In the radio world, most cable connectors are designed to be connected to a radio and pretty much just left connected.  That is why for serious railfanning, though I recognize that it's not practical for a lot of railfans, I recommend using a professionally installed permanenlly mounted vehicle antenna connected to a permanenly mounted mobile radio in a vehicle.  In my case, I have used that setup for years in the vehicles that I use for railfanning.  I essentially use my portable radios only for the times that I am away from my vehicle.



Date: 03/27/24 10:32
Re: Do I need a new antenna?
Author: TCnR

Consider dialing in to the local Weather Broadcast, to have a constant RF signal, then wiggle the existing cable or antenna checking for better or worse reception. That would tell you if the cable or connector is a problem.

Another idea is to exchange the existing antenna with the original rubber antenna, or an aftermarket version, to compare the cable / antenna performance to a simple antenna while monitoring the constant Weather Broadcast. The outside antenna should improve reception in range and stability, but it's something to check.

In general the outside antenna should work better than an antenna on the radio inside the cab. Sometimes there is too much cable loss or damaged cable that screws things up. Sometimes the general location has plenty of adequate transmitters that an outside antenna is simply not worthwhile. That would be somewhere always close to the tracks or with plenty of well placed Dispatcher transmitters, or perhaps an existing relay system.

The well known 'rubber duckie' style antenna is not very expensive, typically $20 or so, maybe $30 if you shop around. I usually have a spare or a different style antenna that can be used as a back up when I have concerns. Make sure you check the integrity of the connector center pins when you swap things around.

+ just checked some prices, add about 10 bucks,



Edited 1 time(s). Last edit at 03/27/24 18:28 by TCnR.



Date: 03/29/24 09:50
Re: Do I need a new antenna?
Author: sf1010

Consider something like this:

https://www.scannermaster.com/Through_The_Glass_Mobile_Antenna_with_BNC_p/15-540721.htm?utm_source=google&utm_medium=cse

I have no personal experience, but they seem to work for some people.  You might be able to take off the little antenna they supply and run cable to your mag mount on the roof.  An antenna in the middle of a metal roof benefits from the roof as a ground plane.

Another possibility is really thin coax.  It is less likely to get beat up by the door.  It has more loss than the fatter stuff, but that probably doesn't matter in your actual use.  You could always get just a foot or so of the thin stuff, and put lower loss cable on both ends.  I've had good luck buying cables from ABR Industries.

https://abrind.com/

Quick delivery, high quality.  I have no financial interest in any company.  

Another source is Pasternack.  I've not dealt with them, but they too have a good reputation.

https://www.pasternack.com/

Lots of other places will also make cables.  Part of the specification of most cables is minimum bend radius -- that may be the most important parameter for your application.

 



Date: 03/30/24 10:02
Re: Do I need a new antenna?
Author: WW

My personal experience is that a "through the glass" antenna has better reception than a rubber ducky antenna inside the vehicle, but not by much.  There is a lot of signal loss because of the glass, and the antenna does not have a good ground plane.    My favorite installation is a permanent roof-mount antenna.  Though it does not have the gain of some antennas, my favorite antenna is the Sti-co Flexi-whip.  The antenna is super-flexible and not likely to hang up in car washes, garage doors, etc.  The antenna shaft itself is very thin and painted black, such that it is barely noticeable from any significant distance from the vehicle.  I've been using these antennas for over a decade with zero problems or failures.  You do have to hunt around to find places that sell them.  They are generally best found from regular two-way commercial radio dealers--that is where I've gotten mine over the years. They are not cheap, but are worth the extra money, in my opinion. 



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