New member with an antenna/cable question

[stealth71]

Hello all, Chris in Montana. Great to be able to make use of all the knowledge and experience here on the forum. So a few questions.

I have two scanners. The first is only for aviation as I use it to feed air traffic control on the web. For an air band only scanner, what would you recommend for both the antenna and the antenna cable? I need an antenna that really pulls in the signal because I'm about 8 miles from the airport and have trees and buildings in the way. Right now I'm using a home made J-Pole. Its OK, but I'd like to do better.

The second scanner is basically for public safety, 150 to 160Mhz roughly, some 450 to 460Mhz as well. What would be a good antenna for this radio and these frequency ranges, as well as other frequencies if needed, and what would be a good antenna cable here as well? I have a box of Orinoco LMR-400 sitting here that I haven't used yet.

Is using two separate antennas the way to go in this instance, or would I just be better off to use one antenna to feed both scanners. My thinking is, if I were to use one antenna, I would then have to buy splitters/amplifiers and all the necessary adapters, so in this case, it might just be cheaper to use two antennas, and that might possibly yield better results anyway by using antennas made for the bands I'm scanning.

Any thoughts? At this point, what I'm really after is suggestions for the antennas to use, as well as what cable to use.

 

[Tubehead999]

New member as well here....I use a discone for scanning to 1200MHZ, several, matter of fact, and have a separate antenna for all my scanners/receivers/transceivers....which is also a very good way to perform comparisons....The discone, relatively inexpensive, would work for your public service needs, as well as your airband interests..... But, have you ever thought about a simple VHF/UHF TV antenna and cut the VHF elements to create your own 'airband yagi'? Very directional, point it at the airport; up to 10db of gain, if tuned correctly; used, they are dirt cheap. Yardsale fodder.... All the values for length of driven element, etc, are available on the web and if you are not satisfied, either with the results or the look, then you haven't lost much.....You can feed it with 70 ohm at the antenna end, real cheap, or my preference RG-58U. Then , either fabricate an inexpensive matching network[if you really want to be pro about it] or tie it to a preselector/active antenna. I am not an expert on the subject, but , tremendous amount of info on this site and others on accomplishing this task. I made a neat dual band antenna 144/440 out of one in the past....worked well. You can take the fabrication as far as you want with a few simple tools and some patience. I would recommend saving that LMR400 for use above 400MHZ and sparingly at that! I use it for my transceivers, with N connectors and all that happy stuff. That cable is expensive! So are N connectors... I use the middle of the road low-loss for my scanners, RG-58U , 4 db loss at 150MHZ, RG-8U, 7 db loss at 150MHZ per 100 feet, and terminate into decent UHF connectors. Again, I have a dedicated antenna for each radio.

Best of luck to you in your endeavors....

 

[stealth71]

I had not thought of cutting my own airband, but that might be a good weekend project some day. I can hear the planes fine, but as for tower and ground, its pretty scratchy. However, I want to see what's going to happen when I swap out the existing RG8 for LMR-400 later this week to see if that helps.

 

[prcguy]

A typical log periodic VHF TV antenna only has 4 or 5dB gain at best and if you change the element dimensions for VHF air band it will have less. There are not many high gain antennas for VHF air band on the market but I will eventually offer plans to construct a 6dBD gain omni or 9dBD gain offset vertical dipole array when I get some time. In the mean time antenna height and low loss coax are your best friends with height being the most important. If you live in an area free of high power paging transmitters or other RF interference you could try a preamp at the antenna to improve the noise figure of your system and make up for feedline loss.
prcguy

New member as well here....I use a discone for scanning to 1200MHZ, several, matter of fact, and have a separate antenna for all my scanners/receivers/transceivers....which is also a very good way to perform comparisons....The discone, relatively inexpensive, would work for your public service needs, as well as your airband interests..... But, have you ever thought about a simple VHF/UHF TV antenna and cut the VHF elements to create your own 'airband yagi'? Very directional, point it at the airport; up to 10db of gain, if tuned correctly; used, they are dirt cheap. Yardsale fodder.... All the values for length of driven element, etc, are available on the web and if you are not satisfied, either with the results or the look, then you haven't lost much.....You can feed it with 70 ohm at the antenna end, real cheap, or my preference RG-58U. Then , either fabricate an inexpensive matching network[if you really want to be pro about it] or tie it to a preselector/active antenna. I am not an expert on the subject, but , tremendous amount of info on this site and others on accomplishing this task. I made a neat dual band antenna 144/440 out of one in the past....worked well. You can take the fabrication as far as you want with a few simple tools and some patience. I would recommend saving that LMR400 for use above 400MHZ and sparingly at that! I use it for my transceivers, with N connectors and all that happy stuff. That cable is expensive! So are N connectors... I use the middle of the road low-loss for my scanners, RG-58U , 4 db loss at 150MHZ, RG-8U, 7 db loss at 150MHZ per 100 feet, and terminate into decent UHF connectors. Again, I have a dedicated antenna for each radio.

Best of luck to you in your endeavors....

 

[Tubehead999]

Sounds like you have a really nice RF block between your site and the airport. You receive the planes fine..but base comms are intermittent....J pole is vertically polarized. And gain is not much...My assumption is that gain is par after all the feedline losses.......a simple vertical would do as well I imagine. You are only 8 miles away......I think that a gain antenna would probably resolve most of your issues. Or more height on your par antenna.

Personnally,I would strap a VOM to your feedline to check resistance before I went to all the trouble to replace coax...most works fine for what you are doing, LMR-400 has a loss of 4.5 db at 150MHZ per 100 feet...RG-8U is around 7db...I don't know how long your cable run is...but it takes 3 db to "double" power. Even the 72-75 ohm stuff will work for what you are doing..if your coax was an issue..ALL signals would have issues, not just the airport base transmissions.

Why don't you try a simple vertical, a piece of stiff wire, cut for1/4 wave at 120MHZ , before swapping out everything? Or. you could actually take a broomstick, some stiff wire, use the Yagi build specs and build yourself a simple Yagi for that region of VHF and see if there is any difference. It is always easier and more time consuming to swap parts than to actually define the issue and generate a resolution for same! Quite frankly, if you take a piece of wire, cut it to 1/4 wave at 120 MHZ and replace the J pole with it, you may be surprised at the results. Just my thoughts on it.....No reflection on anyone, except myself, as I relate this anecdote ; "How can you tell a technician has had a flat tire?" Answer...because you see his or her car on the side of the road with all four tires off of it.....And trust me, I have had all four tires off my car several times in my life............

Best....

 

[stealth71]

But there is something enticing about that UPS truck delivering a shiny new Antenex high gain antenna, LOL!!! I don't know, I think I have a feedline issue, but I won't know for sure until I try the new cable when it arrives.

 

[prcguy]

Please check your facts before posting, LMR400 has about 1.5dB loss for 100ft at 150MHz and typical foam dielectric RG-8 has about 2dB loss + or minus depending on mfr. A J-pole is much better than a simple 1/4 wavelength piece of wire and a little better than a 1/4 ground plane unless the J-pole is broken.
prcguy

Sounds like you have a really nice RF block between your site and the airport. You receive the planes fine..but base comms are intermittent....J pole is vertically polarized. And gain is not much...My assumption is that gain is par after all the feedline losses.......a simple vertical would do as well I imagine. You are only 8 miles away......I think that a gain antenna would probably resolve most of your issues. Or more height on your par antenna.

Personnally,I would strap a VOM to your feedline to check resistance before I went to all the trouble to replace coax...most works fine for what you are doing, LMR-400 has a loss of 4.5 db at 150MHZ per 100 feet...RG-8U is around 7db...I don't know how long your cable run is...but it takes 3 db to "double" power. Even the 72-75 ohm stuff will work for what you are doing..if your coax was an issue..ALL signals would have issues, not just the airport base transmissions.

Why don't you try a simple vertical, a piece of stiff wire, cut for1/4 wave at 120MHZ , before swapping out everything? Or. you could actually take a broomstick, some stiff wire, use the Yagi build specs and build yourself a simple Yagi for that region of VHF and see if there is any difference. It is always easier and more time consuming to swap parts than to actually define the issue and generate a resolution for same! Quite frankly, if you take a piece of wire, cut it to 1/4 wave at 120 MHZ and replace the J pole with it, you may be surprised at the results. Just my thoughts on it.....No reflection on anyone, except myself, as I relate this anecdote ; "How can you tell a technician has had a flat tire?" Answer...because you see his or her car on the side of the road with all four tires off of it.....And trust me, I have had all four tires off my car several times in my life............

Best....

 

[stealth71]

Please check your facts before posting, LMR400 has about 1.5dB loss for 100ft at 150MHz and typical foam dielectric RG-8 has about 2dB loss + or minus depending on mfr. A J-pole is much better than a simple 1/4 wavelength piece of wire and a little better than a 1/4 ground plane unless the J-pole is broken.
prcguy

Thought that seemed a little high as well, but I didn't have time to look it up after I read that post. One of the reasons I went with LMR-400 is because of the low Db loss.