building a 5/8 or Full wave ground plane for Railroad

[walterb]

My goal for this exercise is to have an antenna thats works good and is easy to duplicate. The 3/4" copper pipe just happens to fit inside 1/2" PVC fittings (ok, a force fit) and thats less hardware to deal with. Like others mentioned, it helps the antenna cover a wider bandwidth and the entire antenna should have about 20MHz BW or more.
prcguy

I see. Very good. I priced 1/4 rigid copper pipe this weekend. OUCH! It cost more than the 1/2 inch stuff. I assume because its rare.

 

[PHOENIX_SCANNER]

Question - Murs antenna for RR?

How about this sucker for great RR reception? They include instructions for tuning to a specific frequency by adjusting lengths.

http://www.antennawarehouse.com/VHF-UHF/AWH-150.htm

 

[walterb]

How about this sucker for great RR reception? They include instructions for tuning to a specific frequency by adjusting lengths.

http://www.antennawarehouse.com/VHF-UHF/AWH-150.htm

Looks pretty good, and the price is right, but for now I'm going to build what prcguy comes up with. At some point if I keep this up, I'm going to have this antenna farm of various antennas all tuned to about 161mhz listening for rail traffic..

 

[prcguy]

I only had about 2 hrs to play with the 4 bay dipole array project this weekend but I did get the phasing harness made and checked two elements and half the phasing harness for VSWR. The 2:1 limits are currently at 140 and 161MHz and I'll trim the dipoles a bit to raise the center frequency for general VHF scanner use and a better match on RR freqs. I need to get this finished and on to its new owner so I can scale the dimensions for VHF air band. It should cover the 118 to 136MHz range just fine for scanning and I have never encountered an omni air band antenna that would come close in gain. More to follow....
prcguy

Looks pretty good, and the price is right, but for now I'm going to build what prcguy comes up with. At some point if I keep this up, I'm going to have this antenna farm of various antennas all tuned to about 161mhz listening for rail traffic..

 

[walterb]

I only had about 2 hrs to play with the 4 bay dipole array project this weekend but I did get the phasing harness made and checked two elements and half the phasing harness for VSWR. The 2:1 limits are currently at 140 and 161MHz and I'll trim the dipoles a bit to raise the center frequency for general VHF scanner use and a better match on RR freqs. I need to get this finished and on to its new owner so I can scale the dimensions for VHF air band. It should cover the 118 to 136MHz range just fine for scanning and I have never encountered an omni air band antenna that would come close in gain. More to follow....
prcguy

VERY cool! Is the distance from the dipole to the mast important? Since you brought this design up a few weeks ago, I've noticed some similar to this at our local Fire and Police station, however they span out in 4 directions. I assume this is so they have a broad coverage area?

thanks

 

[prcguy]

Yea, that is one of the important dimensions. You can place the 4 dipoles around the mast with 90deg spacing and it will give you around 6dBD gain omni, place them all on the same side and get around 9dBD gain with a 120deg or wider pattern. I used gaffers tape to stick the dipoles to a mast just for testing. The final version will use two hose clamps per dipole to hold them to the mast.
prcguy

VERY cool! Is the distance from the dipole to the mast important? Since you brought this design up a few weeks ago, I've noticed some similar to this at our local Fire and Police station, however they span out in 4 directions. I assume this is so they have a broad coverage area?

thanks