bcd325p2 computer interference on railroad

[briskattivo]

Just for clarity, I made a youtube video with audio from the local ATC, you can tell that the audio quality is all over the board. But compared to what I was hearing before (which was virtually nothing) it's pretty good! Here it is:

https://www.youtube.com/watch?v=v-CbL4vCV-c&feature=youtu.be

I ordered more duplicate parts last night, so I will have an update hopefully in a similar format when I receive those. Particularly on the railband which was the original objective of this thread. Sorry for the divergence!

P.S. the FM dipole and balun are cheaper on the parts-express page if you don't mind waiting a bit longer. Very tempting to just go bananas on amazon though.

P.P.S. Oh I should have also added I linked to this to see if there were any familiar interference noises that I might not have caught by myself.

 

[briskattivo]

Bear with me. If the formula is 5,626/x=y*0.82=z then "why" is the number to split just y. Where does this z number come into play? If I'm not mistaken if the mean frequency for rail is 160 and the result of 5616/160 is 35.1 which times .82 equals 28.782, then shouldn't each side be 14.391 inches? Another couple trims would probably answer this, but just wondering.

 

[Voyager]

Quarter wave formula is 234/frequency. The result is in feet. Multiply times 12 for inches.
@160 MHz it is 17.55"

 

[RFI-EMI-GUY]

Bear with me. If the formula is 5,626/x=y*0.82=z then "why" is the number to split just y. Where does this z number come into play? If I'm not mistaken if the mean frequency for rail is 160 and the result of 5616/160 is 35.1 which times .82 equals 28.782, then shouldn't each side be 14.391 inches? Another couple trims would probably answer this, but just wondering.

Each side (arm) of a center fed dipole is 1/4 wave. So it is center fed 1/2 wave dipole.

 

[briskattivo]

I'm still a bit confused. So does each arm have two sides (front and back) or do both sides of an arm together count as 1/4? I feel like I just need to pay attention to the original instructions. I found this link which kind of explained it to me, but still a bit fuzzy on the boundary between 1/4 and 1/2 dipole ???

 

[briskattivo]

I got some more dipoles and transformers in the mail today. After experimenting, I guess my conclusion is this dipole works pretty great as an antenna unaltered. Tried a few different lengths/trims, and nothing really worked as well as the unaltered FM dipole. I guess I would have to have one of those antenna analyzers to really know what's up. I have been comparing my scanner's airband reception with the LiveATC broadcast, and it is very close, which is great since it was nearly silent before. Still some frequencies that just don't want to talk though. Railroad is about the same. Trimming doesn't make much of a difference. Couple dispatchers pretty clear though. So sorry for my noviceness on this post, you have all been tremendously informative! It makes me want to start studying for my HAM license so that I can have as solid a base of knowledge.

I don't know what else to say. Any more technological schemes left to recommend? Anything I can do with a budget in the confines of my room are good.

 

[RFI-EMI-GUY]

I'm still a bit confused. So does each arm have two sides (front and back) or do both sides of an arm together count as 1/4? I feel like I just need to pay attention to the original instructions. I found this link which kind of explained it to me, but still a bit fuzzy on the boundary between 1/4 and 1/2 dipole ???

A 1/4 wave dipole is like the little whip extending from the roof of a police car. It is unbalanced, the counterpoise is the metal roof. It has -2.15 dBd gain

What you are making is a "center fed 1/2 wave dipole. It has two 1/4 wave legs. So when you make it 1/2 wavelength your measurement is centered on the "T" where the feed is located. It needs no counterpoise as it is inherent in the design. it has 0 dBd theoretical gain , the second "d" in dBd means dipole. But it isn't so much the gain you are enjoying but the lack of common mode noise coupled on the feedline.

 

[briskattivo]

A 1/4 wave dipole is like the little whip extending from the roof of a police car. It is unbalanced, the counterpoise is the metal roof. It has -2.15 dBd gain

What you are making is a "center fed 1/2 wave dipole. It has two 1/4 wave legs. So when you make it 1/2 wavelength your measurement is centered on the "T" where the feed is located. It needs no counterpoise as it is inherent in the design. it has 0 dBd theoretical gain , the second "d" in dBd means dipole. But it isn't so much the gain you are enjoying but the lack of common mode noise coupled on the feedline.

Yes, thank you! That is the info I was looking for. Is the reason the length works because the wavelengths have a middle phase that the 1/2 wave antenna captures? Or would this work with 1/4 (total) or 5/8?

I discovered something this morning. I have this Nitecore D4 battery charger that usually sits on my desk. And I noticed that when I entered some batteries in there this morning all the airband channels were fluxuating between staticy and non-staticy, so I unplugged it and everything is clear. I think this may be a source of emi from day one of this problem. Still happens no matter what outlet in my room I use, which is annoying but not too much of an inconvenience and worth being able to hear things. Radio interference is so weird! I have noticed as well that if I just move something an inch it can be the difference of whether I hear a frequency at all. And it varies from day to day.

I'm still interested in creating a homebrew antenna/dipole for railroad monitoring use. How important is this antenna analyzer thing and is it really necessary? I have tried the 17.5 length per arm thing and nothing happened. Still considering the Railblade Traintenna. If I can make one for $5 though, that would be better of course! At the moment I can pick up some staticy dispatch communications but no actual train transmissions.

My technique so far has juts been find the length with formula, mark length on dipole with sharpie and tape measure, and cut with scissors. Is this sufficient or do I need to do something else?

Thanks so much!

 

[cmdrwill]

Here is two simple ground VHF antenna:

Build Your Own Antenna – 1/4 Wave VHF Ground Plane Antenna

BUILD A GROUND PLANE ANTENNA FOR 2 METERS AND MORE - SIMPLE AND EASY!

Use a quality connector, prefer N type.

 

[briskattivo]

Yes, thank you! That is the info I was looking for. Is the reason the length works because the wavelengths have a middle phase that the 1/2 wave antenna captures? Or would this work with 1/4 (total) or 5/8?

I discovered something this morning. I have this Nitecore D4 battery charger that usually sits on my desk. And I noticed that when I entered some batteries in there this morning all the airband channels were fluxuating between staticy and non-staticy, so I unplugged it and everything is clear. I think this may be a source of emi from day one of this problem. Still happens no matter what outlet in my room I use, which is annoying but not too much of an inconvenience and worth being able to hear things. Radio interference is so weird! I have noticed as well that if I just move something an inch it can be the difference of whether I hear a frequency at all. And it varies from day to day.

Bonus round: moved toroid core from power supply to charger and that problem is gone now.

Here is two simple ground VHF antenna:

Build Your Own Antenna – 1/4 Wave VHF Ground Plane Antenna

BUILD A GROUND PLANE ANTENNA FOR 2 METERS AND MORE - SIMPLE AND EASY!

Use a quality connector, prefer N type.

cmdrwill, thank you for the links, I will look into these!

 

[RFI-EMI-GUY]

Yes, thank you! That is the info I was looking for. Is the reason the length works because the wavelengths have a middle phase that the 1/2 wave antenna captures? Or would this work with 1/4 (total) or 5/8?

I discovered something this morning. I have this Nitecore D4 battery charger that usually sits on my desk. And I noticed that when I entered some batteries in there this morning all the airband channels were fluxuating between staticy and non-staticy, so I unplugged it and everything is clear. I think this may be a source of emi from day one of this problem. Still happens no matter what outlet in my room I use, which is annoying but not too much of an inconvenience and worth being able to hear things. Radio interference is so weird! I have noticed as well that if I just move something an inch it can be the difference of whether I hear a frequency at all. And it varies from day to day.

I'm still interested in creating a homebrew antenna/dipole for railroad monitoring use. How important is this antenna analyzer thing and is it really necessary? I have tried the 17.5 length per arm thing and nothing happened. Still considering the Railblade Traintenna. If I can make one for $5 though, that would be better of course! At the moment I can pick up some staticy dispatch communications but no actual train transmissions.

My technique so far has juts been find the length with formula, mark length on dipole with sharpie and tape measure, and cut with scissors. Is this sufficient or do I need to do something else?

Thanks so much!

The problems with the formulas is that they are theoretical. You do have to correct for velocity factor which results in shortening the antenna. There is software like NEC that allow you to simulate the antenna and determine such things as the impedance and the radiation pattern. You will find, that yes an antenna might have different modes and at different frequencies act as 5/8 wave and have a different radiation pattern. But NEC is a bit advanced to play with.

An antenna analyzer helps you to determine the resonant tuning frequency. So if you design a 1/2 wave center fed dipole antenna and you make it a bit long, you will find it resonates lower in frequency than desired. As you shorten it the return loss (dip on the analyzer) value will dip to -10, -15 dB or so. If you have a transmitter, you can do same thing with an SWR meter or bidirectional wattmeter. The SWR will improve when resonant.

You might want to look at some of the ARRL's publications on antenna design.

 

[RFI-EMI-GUY]

(snip)

My technique so far has juts been find the length with formula, mark length on dipole with sharpie and tape measure, and cut with scissors. Is this sufficient or do I need to do something else?

Thanks so much!

Yes just make sure you solder the ends of the twinlead back together after you cut!

 

[briskattivo]

The problems with the formulas is that they are theoretical. You do have to correct for velocity factor which results in shortening the antenna. There is software like NEC that allow you to simulate the antenna and determine such things as the impedance and the radiation pattern. You will find, that yes an antenna might have different modes and at different frequencies act as 5/8 wave and have a different radiation pattern. But NEC is a bit advanced to play with.

An antenna analyzer helps you to determine the resonant tuning frequency. So if you design a 1/2 wave center fed dipole antenna and you make it a bit long, you will find it resonates lower in frequency than desired. As you shorten it the return loss (dip on the analyzer) value will dip to -10, -15 dB or so. If you have a transmitter, you can do same thing with an SWR meter or bidirectional wattmeter. The SWR will improve when resonant.

You might want to look at some of the ARRL's publications on antenna design.

Okay, sounds reasonable enough. I did see some options for low budget antenna analyzers on Google. There are a lot of terms I don't understand within radio/electronics. Should I just go on and get my ham license to learn this stuff? As I recall from your numbers before, the velocity factor makes quite a difference in measurements, but I think the reason why I haven't discovered much difference either way will be in reply to your other post.

Yes just make sure you solder the ends of the twinlead back together after you cut!

This. I did not know this. I do remember you mentioning shorting bars or something, but I didn't know what you meant. That explains why every antenna I trimmed pretty much crapped out. I haven't soldered anything in years. This seems pretty low risk though and not as critical as circuit board soldering.

I'm trying to think if I could just do something like connect some line puncturing alligator clips and clip on the ends or if I should solder some extra wire I cut off while cable stripping the dipole (<-- how?). Any thoughts? My airband reception is very good (although I just learned when the washer or dryer is on it gets staticy)

I have a feeling that if I analyze, trim to half wavelength, and then solder the end, trim again to velocity formula if need be and then resolder I can make this happen. Or maybe even skip analyzer and just try by the numbers while soldering. I've been listening to the airband with an unsoldered dipole for the past week in ignorance and even that worked better than my original setup with the diamond, so I think things could only get better! Maybe the analyzer isn't even necessary?

Here's me, doesn't even own a soldering iron, thinking about heading to the store to pick one up. This project is like pandora's box. Not complaining of course

 

[RFI-EMI-GUY]

Get a 25 to 50W soldering iron, cleaning sponge, some solder and solder wick. You will never regret it.

And yes, if the ends of those dipoles were left disconnected you will be happier with the results of them being soldered.

As far as receiving antennas, you can get away with some error because unlike a transmitter the receiver can tolerate a mismatch without damage. However, most antennas are a resonant circuit which means that the closer they are tuned to the receiver frequency and impedance, the better they will work. That said, the bandwidth is often great enough to ignore some error. So try making these antennas without an analyser and see if they meet your current requirements.

 

[briskattivo]

Get a 25 to 50W soldering iron, cleaning sponge, some solder and solder wick. You will never regret it.

And yes, if the ends of those dipoles were left disconnected you will be happier with the results of them being soldered.

As far as receiving antennas, you can get away with some error because unlike a transmitter the receiver can tolerate a mismatch without damage. However, most antennas are a resonant circuit which means that the closer they are tuned to the receiver frequency and impedance, the better they will work. That said, the bandwidth is often great enough to ignore some error. So try making these antennas without an analyser and see if they meet your current requirements.

Sounds like a soldering iron and accessories is a good investment. I haven't quite made it to the store yet, so I did something I used to do when I was younger and trimmed the bulk of plastic around the leads and then melted the coating off with a lighter. Probably not good to breathe in but works. I twisted the wires together and covered them with electrical tape. Took down the airband dipole.

And today I heard very clear transmissions from BNSF and UP dispatch (railroad.) The length is approximately 16 inches on each arm. Not sure if soldering would improve this. I was still disappointed that all I could really hear is the dispatch and what seemed like nothing for actual transmissions coming from the trains, although this is the best I've gotten on my own radio. I get the impression that railroad transmissions are less on the weekends and anything other than day shift. Couldn't compare Railroadradio since it was down, but I tried to record some of the transmissions from the dispatchers on the railband. I kept tinkering with it and had to restart a few times. After 5:00 I heard nothing so couldn't record and gave up.

Probably should try the solder trick. I think the lighter and scissors is the best way to access the actual wire unless there is a safer method though.

I do have a question. Is there some method I can use so that I don't have to completely take down the airband antenna and put up the railband antenna just so that there is no interference? They both work okay so far, but only when they're not anywhere near each other. And taking one down to put another one up is the only solution I've come up with.

 

[RFI-EMI-GUY]

(snip)
1) Probably should try the solder trick. I think the lighter and scissors is the best way to access the actual wire unless there is a safer method though.

2) I do have a question. Is there some method I can use so that I don't have to completely take down the airband antenna and put up the railband antenna just so that there is no interference? They both work okay so far, but only when they're not anywhere near each other. And taking one down to put another one up is the only solution I've come up with.

1) Get some wire strippers and wire cutters! Melting only forces insulation into the strands and makes a mess when soldering.

2) You could cut the antenna long for air band and then install slide switches (quantity 4) one each to short the air band length and then closer in, two more to short the rail band length. This way you could open the inner switches and short the outer and listen to air band, then short the inner switches and listen to rail band. If you are clever, the inner switches (double pole double throw) could be configured to isolate the extension when listening to rail band.

As far as hearing trains vs dispatch. Dispatch likely has a tower 200 -300 feet AGL while antennas on the trains are 20-25 feet at best.

 

[briskattivo]

1) Get some wire strippers and wire cutters! Melting only forces insulation into the strands and makes a mess when soldering.

2) You could cut the antenna long for air band and then install slide switches (quantity 4) one each to short the air band length and then closer in, two more to short the rail band length. This way you could open the inner switches and short the outer and listen to air band, then short the inner switches and listen to rail band. If you are clever, the inner switches (double pole double throw) could be configured to isolate the extension when listening to rail band.

As far as hearing trains vs dispatch. Dispatch likely has a tower 200 -300 feet AGL while antennas on the trains are 20-25 feet at best.

Setup instructions seem pretty legit. I think I could actually do this. I will have to do some research on how exactly, but that should be okay; I think I get the general idea. It may be a little bit before I share an update.

I don't suppose there are any worms eye view solutions to the train vs dispatch problem aside from installing a pylon on my roof is there? Maybe the antenna cmdrwill suggested?

 

[cmdrwill]

You did mount the center fed folded dipole vertically.....

 

[briskattivo]

You did mount the center fed folded dipole vertically.....

cmdrwill? Did you mean "did you mount the center fed folded dipole vertically?" I thought maybe you were suggesting I try reorienting the antenna, so I strung up a big T above my desk/monitoring-area. Points deducted since I felt like I was going eat particle board if I legitimately tried to string it up there.How I have had it has kind of been like a sideways T setup. It is not folded (unless it is somehow) but I had asked if that would help. I have as of yet not tried it. I've included some pictures of my setup. Let me know if anything seems weird about it. I just put it together based on suggestions.

 

[RFI-EMI-GUY]

I assume these pictures are rotated 90 degrees, and the antenna is next ti a windowsill? If so that is hiw it should be fir verticke polarity.