Antenna for 162Mhz RX only

[K5MOB]

I am looking take a 102" whip and cut it down to 72.9" for use as a full wave receive only antenna at 162Mhz.

The antenna will be placed on a tower at 320' AGL.

If the antenna is RX only does it require a ground plane?

I know the antenna will no longer be 50ohms will impedance miss match negatively impact RX?

AT

 

[ko6jw_2]

If a quarter wave is good, a half wave is better and a 5/8 wave is even better, then it stands to reason that a full wave is going to work even better. Actually, it doesn't. A full wave will be difficult to match and it will have an X shaped radiation pattern which may not put the pattern where you want it. A 5/8 wave will probably be optimum. After that you need to stack elements as a collinear vertical to get more gain.

You don't mention what the antenna will be used for other than receiving. You also need to consider the type of coax you will run down the tower. That tall a tower would call for heliax. Otherwise, you will negate the antenna gain and height with loss of signal in the coax.

 

[K5MOB]

Hardline is Andrew LDF4 with LMR400-UF whips to antenna and the AIS receiver.



When you say radiation pattern, are you talking about RX pattern? I am sorry if its a goofy question, I have not played with two way sense the collage CB days.. I have been in microwave for some time and we bounce everything of a parabolic dish.. I can not find my copy of my ARRL Antenna book to brush up on monopole theory.

by stacking the elements in a collinear vertical are you suggesting not using a solid monopole.

If I remember correct, collinear vertical is set up connecting the center pin of the first element to the outside of the second then the center of the second to the outside of the third one would continue off setting and stacking the elements to achieve the desired gain. Each element would be 5/8 wave.

That would take a lot of time to build and case. it would be more practical to just buy a 5/8 pre made antenna..

If that is the case, Who makes the best 5/8 gain antennas?

AT

 

[WA0CBW]

Just a thought but an antenna at that elevation will take a beating from the weather. I would suggest a commercial antenna that is designed to withstand the elements.
BB

 

[K5MOB]

Just a thought but an antenna at that elevation will take a beating from the weather. I would suggest a commercial antenna that is designed to withstand the elements.
BB

I kinda came to that conclusion in the last post.. Sigh..

The reason for the thought of making something was a 21 ft Shakespeare does not fair well at 300 ft on a 48" stand off it will flex enough for the top section to contact the tower.

I currently have the 21' shakespeare 10db at 200 ft and have made a fiberglass support that attaches where the upper and lower sections of the shakespeare meet and have the other end of the fiberglass support attached to one of my torque arms. The guy who owns this AIS receiver would like to be higher but on the commercial 4' 3db AIS antennas at the top we get no better range than the 21' shakespeare at 200 ft.

So I am in a hard spot. Today I have been searching for a 6 element loop antenna for 162mhz as I can attach it with three two point mounts. Otherwise I will have to make a new mount for the 21' that does not require mounting to the torque arm.

I would image the 21' shakespeare and the 4' AIS are both a collinear design so the whip idea I had would have given me even less gain. I guess that idea got out of the gate a little bit premature!

AT

 

[mmckenna]

At 327 feet above ground level, you may run into some issues.

327 feet of 1/2 inch heliax is going to result in a bit over half your signal being lost. Not a deal breaker, but something to consider.

At that height, you might pick up more than one WX transmitter on some frequencies. If you are looking to listen for a specific station you might want to consider a directional antenna.

At 327 feet, any issues with that antenna are going to be an issue to fix. Even if you are an experienced tower climber yourself, climbing that far isn't what I'd call fun. Specific base antennas are used for a good reason. A modified CB mobile whip will work, but long term durability might be an issue. Unlikely the whip itself is going to fail, but the mounting might be an issue. I'd hope you were considering a custom designed mount, and not an off the shelf mobile mounting bracket. Most of those use UHF connectors and may be very difficult to properly seal.

A full wave antenna might sound like a good idea, but there are issues. I'd look at something like a co-linear base antenna if you really want an omni-directional pattern. Using the tighter beam width focused out towards the horizon will probably work much better than a funky pattern of a full wave whip. Also, a purpose built base antenna will last a lot longer.

Should be pretty interesting what you hear at that height.

 

[mmckenna]

If the antenna is RX only does it require a ground plane?

Unless you are using a ground independent design, the ground plane helps. Even with a half wave antenna, which doesn't technically require a ground plane, adding one increases gain by 2.5dB or so.

 

[K5MOB]

At 327 feet above ground level, you may run into some issues.

327 feet of 1/2 inch heliax is going to result in a bit over half your signal being lost. Not a deal breaker, but something to consider.

Maybe that is the issue we are having when we move to the top.. I have a 1" line going up to the top that is no longer in use. I will try to move to it.

At that height, you might pick up more than one WX transmitter on some frequencies. If you are looking to listen for a specific station you might want to consider a directional antenna.

We are only looking to pick up AIS 87B (161.975 MHz) and 88B (162.025 MHz)

At 327 feet, any issues with that antenna are going to be an issue to fix. Even if you are an experienced tower climber yourself, climbing that far isn't what I'd call fun. Specific base antennas are used for a good reason. A modified CB mobile whip will work, but long term durability might be an issue. Unlikely the whip itself is going to fail, but the mounting might be an issue. I'd hope you were considering a custom designed mount, and not an off the shelf mobile mounting bracket. Most of those use UHF connectors and may be very difficult to properly seal.

We own 27 towers that span 4 parishes, I have climbers that trip 1k feet per day. We are a Microwave Based ISP for the Oil Field and rual communities.. 2-Way is not our normal market Infact the only 2-way stuff I have is the AIS on my 320' I have a Fire Dept repeater on one of my 250' towers and a pager transmitter on one of my 140' towers. The Fire Dept and Pager companies take care of most of the stuff with their equipment we just climb for them. We seal coax connections up in salt environments on the daily basis.

A full wave antenna might sound like a good idea, but there are issues. I'd look at something like a co-linear base antenna if you really want an omni-directional pattern. Using the tighter beam width focused out towards the horizon will probably work much better than a funky pattern of a full wave whip. Also, a purpose built base antenna will last a lot longer.

My other post has not been approved yet, it covers what you stated here.

Should be pretty interesting what you hear at that height.

This is indeed true.. I have a local HAM guy that wants to put a SDR on this tower just to see what he can pick up... He is looking to stream the Police, Fire, EMS traffic over the internet. As we are in the process to upgrading to smart jack radios, I have a bit more cleaning up to do on this site and will then have additional hardline that will be not in use. Once I have every thing changed out I will let the HAM guy install the SDR.

AT

 

[prcguy]

Put the 21ft Shakespeare up and use an insulated top clamp to keep the antenna from whipping around. The top clamps are a thick fiberglass pole that mounts rigid to the tower and also clamps to the upper part of the antenna.

The high gain and extra height will help offset the cable loss but reducing the loss will further improve things. BTW your 21ft Shakespeare has about 5dB gain, not 10. The advertising people stretch the specs to make more sales.
prcguy

 

[mmckenna]

OK, AIS, that makes more sense than what I was assuming.

At 327 feet, you should get some great coverage.
Since all your targets will be sitting at the horizon, or lower, you should really consider your antenna pattern carefully. Something with a bit of down tilt might be more productive.

The losses in 1/2" heliax should be fine if you are using a good receiver and an antenna with some gain. If feedline losses were still a concern, a tower top amplifier might be a good option.

I work at a site that's at about 800 feet above sea level and looking out over the Pacific Ocean. I don't have any AIS gear to try out, but I do have an ADS-B receiver here. Even at 1.09gHz, I regularly pick up aircraft 300+ miles out. Of course they are at 38,000 feet, but still, pretty good coverage. I've got a remote controlled receiver that covers 40kHz to 3.5gHz at one of our tower sites, and the coverage is pretty good.

Should be really interesting to see not only how well the AIS system works, but how well the SDR works. It's a lot of fun when you have access to these sites and can set up your own projects.

 

[prcguy]

A break point for considering down tilt is a 10dBd omni (about 7deg vertical beam width) and more than 1,000ft above average terrain. This was quoted to me by Engineers from both Decibel Products and Telewave.

Since the OPs best antenna is estimated about 5dBD gain and about 327ft high, down tilt is not necessary.
prcguy

OK, AIS, that makes more sense than what I was assuming.

At 327 feet, you should get some great coverage.
Since all your targets will be sitting at the horizon, or lower, you should really consider your antenna pattern carefully. Something with a bit of down tilt might be more productive.

The losses in 1/2" heliax should be fine if you are using a good receiver and an antenna with some gain. If feedline losses were still a concern, a tower top amplifier might be a good option.

I work at a site that's at about 800 feet above sea level and looking out over the Pacific Ocean. I don't have any AIS gear to try out, but I do have an ADS-B receiver here. Even at 1.09gHz, I regularly pick up aircraft 300+ miles out. Of course they are at 38,000 feet, but still, pretty good coverage. I've got a remote controlled receiver that covers 40kHz to 3.5gHz at one of our tower sites, and the coverage is pretty good.

Should be really interesting to see not only how well the AIS system works, but how well the SDR works. It's a lot of fun when you have access to these sites and can set up your own projects.

 

[mmckenna]

A break point for considering down tilt is a 10dBd omni (about 7deg vertical beam width) and more than 1,000ft above average terrain. This was quoted to me by Engineers from both Decibel Products and Telewave.

Since the OPs best antenna is estimated about 5dBD gain and about 327ft high, down tilt is not necessary.
prcguy

Makes sense. I've got 9dB 800MHz antennas at about 900 feet on a hill. They've got 3˚ down tilt and it seemed to make a difference in some of our buildings compared to a pair of antennas with no downtilt.

 

[K5MOB]

Well just thought I would give a update to this post..

We attempted a few things.

We used a single use 4db AIS tower mounted antenna - This sucked about 5 to 8 mile range.

We used the 21 foot unit and it worked good until we mounted the stabilizer clamps to it. The range would reduce from 18 miles to 10.

We ended up getting a Tram 1490 and mounting it to unistrut at the bottom i took a pice of sch 80 1.25" PVC electrical conduit and slid over the antenna. This buts up nicely to the metal mount that holds the ground plane rods. I cut the PVC off at 9ft this is 1 ft longer than the antenna. I place a bit of armaflex pipe insulation about 6 inches from the end of the antenna to keep it center in the PVC and put spray foam in the end of the pipe. I trimmed off the excess foam and capped the PVC. Now this gives me a place to attached a second unistrut above the end of the antenna to stabilize the antenna in high wind.

This setup at 150 feet will receive from 20 to 22 miles, and at 300 feet will receive from 32 36 miles.

In the process of all this I got my Ham Ticket I am now KG5MKT and awaiting my vanity call of K5MOB. We moved the local Ham 2 Meter Repeater to this 320 ft. I also got a GMRS ticket WQXL267 I am going to be installing a GMRS repeater on this tower also.

73
KG5MKT

 

[toastycookies]

Well just thought I would give a update to this post..

We attempted a few things.

We used a single use 4db AIS tower mounted antenna - This sucked about 5 to 8 mile range.

We used the 21 foot unit and it worked good until we mounted the stabilizer clamps to it. The range would reduce from 18 miles to 10.

We ended up getting a Tram 1490 and mounting it to unistrut at the bottom i took a pice of sch 80 1.25" PVC electrical conduit and slid over the antenna. This buts up nicely to the metal mount that holds the ground plane rods. I cut the PVC off at 9ft this is 1 ft longer than the antenna. I place a bit of armaflex pipe insulation about 6 inches from the end of the antenna to keep it center in the PVC and put spray foam in the end of the pipe. I trimmed off the excess foam and capped the PVC. Now this gives me a place to attached a second unistrut above the end of the antenna to stabilize the antenna in high wind.

This setup at 150 feet will receive from 20 to 22 miles, and at 300 feet will receive from 32 36 miles.

In the process of all this I got my Ham Ticket I am now KG5MKT and awaiting my vanity call of K5MOB. We moved the local Ham 2 Meter Repeater to this 320 ft. I also got a GMRS ticket WQXL267 I am going to be installing a GMRS repeater on this tower also.

73
KG5MKT

And so it begins.

 

[mancow]

Imagine the WX transmitter intermod at that elevation and gain !

 

[N3JI]

I believe the grey conduit is less than ideal because it has some kind of material in it not transparent to RF. To be fair, I haven't checked into it myself, but I have built some home-brew antennas, and everything I've read is to stay away from using grey as radomes... Just FYI -- if yours is working to your satisfaction, leave it be. Maybe something to consider for next climb or replacement.

Here is a quote and a source. Not sure of the validity, but it is something to consider: "NOTE: IN THIS PROTOTYPE, GRAY PVC WAS USED. IT IS HIGHLY RECOMMENDED THAT YOU USE WHITE PVC. GRAY HAS MUCH MORE ATTENUATION TO RF THAN WHITE!"

Source: http://www.hamuniverse.com/vertbazooka.html

 

[NDRADIONUT]

In fact the low pressure thin wall white stuff is the best to use...

 

[phillmobile]

Use a folded dipole then you can use then antenna for other things at the same time and have a wide flat response.
Folded dipoles always win in my opinion.

 

[K5MOB]

And so it begins.

Yep, I am all in the KoolAid.

I have picked up quite a tool box in the past few weeks. I have a Kenwood TKM-707 Marine SSB I modded it for the HAM band I also picked up a R-5000. I picked up 2 Baofeng BF-F9V2+ HTs and 2 BTECH UV-5001 mobile units.

The wife is studying to get her ticket also!

I got my vanity a few days ago.

Now I just need to go test for my general to play on the HF rig..

73
K5MOB