thanks for that info chief21. experience is the best teacher!
VHF Base station antenna
- Thread starter Rawkee1
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I.m torn as to what the highest db gain antenna is best for me at about 158-161mhz. now I'm thinking of an amplifier at the base of the antenna while I'm up there. Where can I buy a good amp for my application?
prcguy
Member
The highest gain you can get in a given size is a dipole array and a 4-bay gives right around 6dBd omni gain in about 21ft of antenna including mount. There is no other antenna design that will equal or exceed that unless you go a lot bigger.
Many antenna mfrs make up gain numbers and some will try and get you to believe their 12ft fiberglass thing has 11dB gain or some other nonsense. Bottom line is its all nonsense and lies. You can also get a 4-bay dipole array that actually covers 150 to 17MHz continuous without tuning and some models cover the 136 to 174MHz range with no tuning. You want big gain and big band width? Dipole array is it.
Placing an amplifier at the base of the antenna can be beneficial but you really have to consider a low loss tight skirt band pass filter ahead of the preamp. If you live out in the boonies with no TV, FM or other transmitters in your town you might get away without a filter. In Auburn near Worcester, I doubt you will have good success without a filter.
Many antenna mfrs make up gain numbers and some will try and get you to believe their 12ft fiberglass thing has 11dB gain or some other nonsense. Bottom line is its all nonsense and lies. You can also get a 4-bay dipole array that actually covers 150 to 17MHz continuous without tuning and some models cover the 136 to 174MHz range with no tuning. You want big gain and big band width? Dipole array is it.
Placing an amplifier at the base of the antenna can be beneficial but you really have to consider a low loss tight skirt band pass filter ahead of the preamp. If you live out in the boonies with no TV, FM or other transmitters in your town you might get away without a filter. In Auburn near Worcester, I doubt you will have good success without a filter.
VHF 108-174 MHz Dipole Antennas
I agree imonitor. those commercial dipole's start at $349. What antenna do you recommend from that site? That 108-174 Dipole antenna. is that the commercial one?
I hesitate to make a recommendation as I do not have experience with any of them and they are fairly expensive. I sent the link as they have a few choices that meet your criteria.
Ubbe
Member
The PGA103+ are the most cost effective of them. Low noise and can handle strong signals. You can get one from GPIO Labs that are only circuit boards, they are on ebay, and either install in a waterproof box or put it it up in the end of the tube that holds the antenna, if you get that kind of installation. The exact same thing but in a box with connectors can be had from MiniCircuits, it has a 103+ name and will cost conciderable more.
If you get an amplifier that can be powered from the coax it will be an easier installation but you will need a bias-T device to power the coax. It's just a coil and a capacitor in a metal box with connectors that you can solder together yourself as the ones you buy are usually way overpriced.
/Ubbe
I'm looking into the Tram 1490. It appears it covers my needs and is 7/8 wave. How do you knowledgeable scanner enthusiasts rate this antenna with LMR400 coax? I am open to suggestions.
mmckenna
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Tram is the Cheap Chinese Radio/Baofeng of antennas.
Sure, they'll work fine, for a while. But they are not commercial quality antennas by any stretch of the imagination. If you need an inexpensive antenna and your budget is tight, it'll do what you need, but don't expect it to last as long as a higher quality antenna.
Please suggest a good quality antenna.
mmckenna
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What is your budget?
prcguy
Member
This is what you will find with just about all antennas advertised for wide frequency ranges like 144 to 174MHz. They don't advertise that the antenna only covers a couple of MHz at best and needs to be cut for your specific frequency. Here is the cutting chart for the Tram 1490.
Wide band antennas with gain are usually very large and very expensive but they sometimes show up cheap on eBay. I've bought many commercial 4-bay dipole arrays that cover anywhere from 136 to 174 or most of that range without tuning and the most I've paid on eBay is $75. You just have to keep looking every week for a deal because most of these are well over $1k new.
Wide band antennas with gain are usually very large and very expensive but they sometimes show up cheap on eBay. I've bought many commercial 4-bay dipole arrays that cover anywhere from 136 to 174 or most of that range without tuning and the most I've paid on eBay is $75. You just have to keep looking every week for a deal because most of these are well over $1k new.
Any thoughts on this Lasen BSA150C?
mmckenna
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It's an NMO-150 mobile 5/8th's wave antenna on an NMO-base adapter. It's going to perform like any other 5/8th's wave mobile antenna. It's going to have narrow bandwidth. You'll have about 12MHz of less than 2:1 SWR:
Ubbe
Member
I have my Diamond F23H cut to 155Mhz and my local airport tower use 118MHz and the 3 element yagi are better at 118Mhz but the Sirio 5/8GP cut to 118Mhz are worse, and they all sit at the same location. There's so much gain from the F23 that it still makes the out of band frequencies have enough gain compared to a standard GP.
Don't be afraid of SWR. A bad SWR of 2:1 are a 10% loss. Lets say you have a weak signal of 0,5uV which is -113dBm. Then a 10% loss equals to a 0,45uV signal which is -114dBm. It's 1dB of loss. Use an amplifier and you will gain that loss back and the lower noise figure will add another 3-4dB. A very bad SWR of 6:1 are a 50% loss, that's 3dB.
/Ubbe
Don't be afraid of SWR. A bad SWR of 2:1 are a 10% loss. Lets say you have a weak signal of 0,5uV which is -113dBm. Then a 10% loss equals to a 0,45uV signal which is -114dBm. It's 1dB of loss. Use an amplifier and you will gain that loss back and the lower noise figure will add another 3-4dB. A very bad SWR of 6:1 are a 50% loss, that's 3dB.
/Ubbe
My budget was to stay between $175-$250 not counting the new coax. I believe that I should be able to have a decent setup for that. BCD996P2 x2 plus Radio Shack pro2067. Thinking about the SDS200 but have to apply the brakes on that for now. The 996's do ok, but I wish they had a quicker scan rate. I have a Moonraker M100 preamp that doesn't seem to do much.
mmckenna
I ♥ Ø
That's a pretty good budget for a hobbyist, but there will be tradeoffs. You'll have a hard time getting full VHF band coverage with high gain at that price. For wide bandwidth, the folded dipoles are hard to beat, and they are very durable. To get the gain, you'll need multiple phased dipoles. That gets expensive unless you build your own.
I've used Telewave folded dipoles on UHF, and they work well. But you won't get a new one in your budget range. Maybe used, if you can find one.
There are other brands that would be less expensive.
But like many have said here, there are tradeoffs, and you need to decide on what you are willing to sacrifice to stay within your budget.
The higher gain verticals will give you the gain at the expense of the bandwidth.
The lower gain dipoles will give you the bandwidth at the expense of the gain.
You can combine dipoles to give you the gain back, but it gets expensive. A multiple bay system of folded dipoles will give you gain + bandwidth, but no where near what your budget is. Making your own is a good option, and it'll teach you a lot.
Finding a middle ground and staying within your budget is something you need to grapple with. As you've seen above, there are a couple of approaches. Which one works best for you is something you need to decide.
Ubbe
Member
I didn't notice my mistake when I wrote it and didn't proof read. I woke up 2am when my brain where doing housekeeping and processing all events the previous day and made we aware of the error.
It should say: "Lets say you have a weak signal of 0,45uV which is -114dBm. Then a 10% loss equals to a 0,50uV signal which is -113: dBm. It's 1dB of loss."
Amplifiers, if installed at the antenna, works as a buffer and isolate the SWR to the antenna and keep a low SWR to the coax. My experiance are that the worse the antenna with high SWR the more use of an amplifier. The most improvements I've seen when testing where when I removed the antenna rod from a magnet mount and only used the foot. When listening to a weak signal and then adding an amplifier made the signal increase to noise free, probably almost a 10dB increase in signal/noise relation. In a perfect antenna/coax system an amplifier "only" reduce coax loss and improve internal noise level a few dB, if it is a low noise amp, but in a mismatch system the improvements are so much more, perfect for scanner use where you want as much frequency bandwidth as possible from an antenna. Also remember that a scanners impedance are not a perfect 50 ohm over its frequency range. The band filter solution would be too complicated and expensive. It will load the coax with different impedances that create SWR but using an isolating splitter between scanner and coax, a $5 1-2 CATV splitter are fine, will keep a constant impedance to the coax.
/Ubbe
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