2m Band Antenna Opinion

[MetalCarnage]

Posted originally in Eastern Canada but did really get a variety of opinions, just got one so i decided i would post here and try to get a little more input.

I have a BCD796D installed in my Grand Prix and have been using a Maldol EX-104 Antenna which at the 2m band is rated as a unity gain antenna.

My main problem is i am listening to a P25 system (140's) and am getting zones of weakness that lead to periods of transmissions getting completely cut out as the scanner motorboats/hits big error #'s.

So i was looking at a little bit bigger antenna with a gain of 2.9 dBi in the 2m band. The one opinion i got is that going from unity gain to 2.9dBi would make no difference on how strong i pull in signals (aka my P25 wont improve since right now i am only getting 2 out fo 7 bars at times). I have heard other ppl say with my scanner they could pull in the same towers from 80-90kms away with great strength, where i only get 2-3 bars once i get 40kms away. So in my mind anything above unity gain should make at least a bit of difference.

If anyone could chime in on whether the single opinion is accurate or if there is a chance an antenna with higher gain would make my digital a little better, that would be great. Thanks in advance.

 

[MetalCarnage]

Wirelessly posted (LGE-LG260 POLARIS-LG260/2.0(GUI) MMP/2.0)

Anyone?

 

[jim202]

Bottom line is any antenna gain will improve the received signal level. The real question is this
3 db gain going to be enough to satisfy your receiver to hear the system good enough.

I think your expecting more than you should from a long distance. The real signal strength
that arrives at your antenna from a distance of 40 kms away as you state, will depend on
a number of factors. Most of them will be dependent on the terrain. Just how flat or
hilly will be a big factor. What the foliage is between you and the transmitter will
play a big part in how well or how poorly your chances are of pulling in the signal. Then
there is the question of just how far up in the sky the transmitting antenna is and how
much gain it has.

You can't change the laws of physics, Path loss is loss no matter how you try to play
with the numbers. You can improve the received signal by lower losses. About the only
place you can effect this is in your coax cable and antenna gain. Use better coax that
has lower losses and a high antenna gain that compensates for a fraction of the path loss.

What ever someone else tries to tell you would probably fall into the old wife's tales list.

Jim

 

[poppafred]

Antenna Problem?

You did not mention which band you were trying to listen to at the time. I will "assume" you are working on trying to receive 800 MHz.

The problem is going to be that any gain you might get on 2m is going to be wasted on a scanner. The 2m antenna is designed to resonate on 144 MHz and is not going to be as sensitive to signals in the 400 or 800 MHz range as an antenna designed specifically for a scanner. It is like trying to get a "C" note out of a "G" string on a guitar. It is possible but you have to shorten the string physically by fretting it. The "C" is in there but the string really likes the "G" better.

Believe it or not, the best antenna I have found so far to use on my Pro-197 for listening to 800 MHz signals is the rubber ducky off my Pro-97 portable. I can hear the local 800 MHz P25 tower as well on it as I can on a 2m antenna up at 39 feet. The antenna at the top is a Cushcraft ARX2B with a 5db gain on 2m. The coax from the antenna to the radio room is hardline. I have to put a barrel connector & a 25' run of RG8X to get to the scanner in the living room. The signal loss from the RG8X coax run and non-resonance is amazing. I can sit in my recliner and switch around antennas and watch the resulting signal strength. I picked a tower with a decent signal and swapped over to a 2m base load Larsen mag mount I use for weather reporting during lightning storms. I had 2-3 bars. On a dualband 2m/440 1/4 wave, the signal dropped to 1 bar. With the ducky, I have 4, sometimes 5 bars and the tower was at 99%. Go figure.

Mobile ops are a totally different animal. "Motorboating" or signal flutter is going to be hard to get rid of on an antenna meant for a particular service (in your case, 2m). The ratio between "DB" and "S" units is 6:1, if my memory has not completely failed me. So, 3 db will give you about half an "S" unit more. You might want to consider finding a broadband preamp to boost the incoming RF or look for a resonant antenna.

On that last option, you can buy a mag mount cell phone antenna pretty cheap. I have a small mag mount cell antenna with an adapter from their standard thread-on FME connector to BNC. I does a surprising job on P25 signals within 25 miles (40 kilometers). Radio Shack sells one for $14.99 that resonates very well in the 800 MHz band. Even offers a 2 db gain in that spectrum. You can see it at: Wilson Electronics Dual-Band Magnet Mount Antenna - RadioShack.com if you are interested. Mine is 24 years old and wearing out but I will replace it with this one some day. As a matter of fact, I may get one next month just to have a spare. And I can hear 144 MHz & 450 MHz on it fairly well so I am not really missing very much.

Once again, it is mainly a matter of resonance.

 

[MetalCarnage]

You did not mention which band you were trying to listen to at the time. I will "assume" you are working on trying to receive 800 MHz.

The problem is going to be that any gain you might get on 2m is going to be wasted on a scanner. The 2m antenna is designed to resonate on 144 MHz and is not going to be as sensitive to signals in the 400 or 800 MHz range as an antenna designed specifically for a scanner. It is like trying to get a "C" note out of a "G" string on a guitar. It is possible but you have to shorten the string physically by fretting it. The "C" is in there but the string really likes the "G" better.

Believe it or not, the best antenna I have found so far to use on my Pro-197 for listening to 800 MHz signals is the rubber ducky off my Pro-97 portable. I can hear the local 800 MHz P25 tower as well on it as I can on a 2m antenna up at 39 feet. The antenna at the top is a Cushcraft ARX2B with a 5db gain on 2m. The coax from the antenna to the radio room is hardline. I have to put a barrel connector & a 25' run of RG8X to get to the scanner in the living room. The signal loss from the RG8X coax run and non-resonance is amazing. I can sit in my recliner and switch around antennas and watch the resulting signal strength. I picked a tower with a decent signal and swapped over to a 2m base load Larsen mag mount I use for weather reporting during lightning storms. I had 2-3 bars. On a dualband 2m/440 1/4 wave, the signal dropped to 1 bar. With the ducky, I have 4, sometimes 5 bars and the tower was at 99%. Go figure.

Mobile ops are a totally different animal. "Motorboating" or signal flutter is going to be hard to get rid of on an antenna meant for a particular service (in your case, 2m). The ratio between "DB" and "S" units is 6:1, if my memory has not completely failed me. So, 3 db will give you about half an "S" unit more. You might want to consider finding a broadband preamp to boost the incoming RF or look for a resonant antenna.

On that last option, you can buy a mag mount cell phone antenna pretty cheap. I have a small mag mount cell antenna with an adapter from their standard thread-on FME connector to BNC. I does a surprising job on P25 signals within 25 miles (40 kilometers). Radio Shack sells one for $14.99 that resonates very well in the 800 MHz band. Even offers a 2 db gain in that spectrum. You can see it at: Wilson Electronics Dual-Band Magnet Mount Antenna - RadioShack.com if you are interested. Mine is 24 years old and wearing out but I will replace it with this one some day. As a matter of fact, I may get one next month just to have a spare. And I can hear 144 MHz & 450 MHz on it fairly well so I am not really missing very much.

Once again, it is mainly a matter of resonance.

Hey Poppafred, as stated in my first posting i am trying to listen to the 140mhz or 2m band range

 

[MetalCarnage]

Bottom line is any antenna gain will improve the received signal level. The real question is this
3 db gain going to be enough to satisfy your receiver to hear the system good enough.

I think your expecting more than you should from a long distance. The real signal strength
that arrives at your antenna from a distance of 40 kms away as you state, will depend on
a number of factors. Most of them will be dependent on the terrain. Just how flat or
hilly will be a big factor. What the foliage is between you and the transmitter will
play a big part in how well or how poorly your chances are of pulling in the signal. Then
there is the question of just how far up in the sky the transmitting antenna is and how
much gain it has.

You can't change the laws of physics, Path loss is loss no matter how you try to play
with the numbers. You can improve the received signal by lower losses. About the only
place you can effect this is in your coax cable and antenna gain. Use better coax that
has lower losses and a high antenna gain that compensates for a fraction of the path loss.

What ever someone else tries to tell you would probably fall into the old wife's tales list.

Jim

I didnt think i was expecting too much from a long distance when someone else on here said they could get the same towers as myself mobile in his car from over 80kms away when i can only get them to be max 45-50kms.....so maybe he was just BS'ing?

 

[smason]

Where on the car is your antenna mounted?
In my experience on 2m a 1/4 wave whip on the roof routinely beats a 5/8 wave on the trunk.

 

[mike_gain]

2.9dbi is less than 1 db over unity. Compare antennas using dbd.

 

[MetalCarnage]

Where on the car is your antenna mounted?
In my experience on 2m a 1/4 wave whip on the roof routinely beats a 5/8 wave on the trunk.

It is mounted on the trunk, and unfortunatly will not be making any appearance on the roof, too much of hastle to deal with a mag mount. Need to stick with the discreet Trunk Lip NMO mounts.

dbi, dbd, all the same....like saying use feet instead of meters, whatever way you read it, still results in the same thing....who the hell uses feet...lmao

I guess i will just bite the bullet and get an antenna with a little gain and hope for the best

 

[N3LLO]

On a side note, it should be realized that height, terrain and obstructions at those distances can make much more difference than a couple dB of gain on the antenna. The person making the claim could've been on a hilltop with line-of-sight to the transmitter, whereas you may be in a deep hole, surrounded by mountains. Those are two drastically different reception scenarios.

 

[mike_gain]

I understand the feet/meters thing. The point I was making is that if someone sees a gain figure of 2.9dbi , they may think it's way,way better than unity.

 

[mrweather]

If you've already got the NMO mount get a Larsen NMO150 base coil and whip. Don't trim the whip and voila, a 5/8 wave antenna for 140 MHz.

It will have more theoretical gain than the Maldol (since it's only an end-fed 1/2 wave) and will be more durable.

My 2 cents.

 

[MetalCarnage]

On a side note, it should be realized that height, terrain and obstructions at those distances can make much more difference than a couple dB of gain on the antenna. The person making the claim could've been on a hilltop with line-of-sight to the transmitter, whereas you may be in a deep hole, surrounded by mountains. Those are two drastically different reception scenarios.

True enough....although, as far as mountains go....i live in southern ontario.....i think the biggest "Mountain" around here is probably a manmade pile of dirt, lol, pretty much flat everywhere where i live.

Mr. Weather...i will give that a go i guess and see what happens...

 

[W2NJS]

P25 Monitoring

My personal experience with this subject indicates that the transmitting antenna setups for digital systems are similar in their setups to cell phone installations. That means that the area of transmit coverage is well defined so that the signal stays, as much as possible, in its service area. This is NOT the case with conventional analog systems where you can monitor the 154 mHz FD signal DFQ from three counties away. I run a Motorola mobile as a fixed station 800 mHz trunked monitor and I first tried an inside antenna because I'm only a short distance from the county "cutoff" line. The inside antenna gave me nothing but hash, noise, burps, and packet loss until I switched to my 900 mHz 10db gain roof antenna which solved the problem. I also have an idea that the P25 systems run at relatively low power, so between antenna downtilts and low power you have a good recipe for lousy signal reception EXCEPT when you're driving in the signal's actual intended service area. A 5db gain mobile antenna on an NMO mount is also highly recommended; it seems to be the industry standard on every public service vehicle I see.