VHF Base station antenna

Rawkee1

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In all the replies, many of you had great information. I saw this antenna below. I would like to know if I'm better off spending more money and purchasing a commercial grade antenna like this one with at least LMR400 cable. Any recommendations are greatly appreciated. This particular antenna runs about $360.00.
Commscope DB222-A
 

mmckenna

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Better than a lot of the ham/hobby stuff. I haven't worked with those in particular, but it looks like the coax is fully exposed. Might not last as long as the more expensive antennas, but that's the trade off with the lower price.

What's your RF environment like? Are you in the relative center of the things you want to listen to, or are they generally in one direction away from you?

Reason I ask is because depending on how you orient the bays on that antenna, it'll change your performance. If you point them in one direction, it makes it slightly directional and gives you some more gain (6dB is their claim, it's probably more like 3 to 6dBd depending on the spacing from the mast).
If you are in the center of what you want to listen to, then you'll put the bays on opposite sides of the mast and you'll get a more omni directional pattern but only 1/2 the gain.

You may not need lots of gain for what you are doing. A single dipole might give you some more flexibility, and adding a preamp at the antenna may give you the additional gain you desire. I really like the Telewave ANT150d. It'll cost you more, and probably not necessary for what you are doing, but a single dipole might be all you need. Easier to install, easier to adjust the pattern.
 
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prcguy

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Its only got 3dBd gain omni and doesn't quite cover your original frequency range request of 150 to 170MHz.

In all the replies, many of you had great information. I saw this antenna below. I would like to know if I'm better off spending more money and purchasing a commercial grade antenna like this one with at least LMR400 cable. Any recommendations are greatly appreciated. This particular antenna runs about $360.00.
Commscope DB222-A
 

Rawkee1

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Bottom line is, you do the best you can with what you got. Thank god that Radioreference has many intelligent members that will offer their expertise to help. To be a serious listener, it costs money but what hobby doesn’t. It would be nice to rent an antenna up high on a tower and pay by the month. So much for dreaming. Being an New Englander, I have a short window of time to improve my setup before the flakes fall. May December the Diamond F23H would be a nice one to try. I’m sure it will out preform a discone that’s up there. Trial & error is costly though. The fact of the matter is, what works for someone wount necessarily work for the next guy. There are a lot of factors such as location, height, radio equipment and so on…….
 

Ubbe

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I would like to know if I'm better off spending more money and purchasing a commercial grade antenna
The difference would only be that it would last much longer. I know professional grade antennas that have been up 50 years and still perform great. Amateur type antennas use cheaper materials and their glasfiber cracks and elements corrode. I would say that after 10 years you will have to take a cheap antenna down and dismantle it and inspect and fix cracks and corrosions. The actual performance of cheap and expensive antennas are usually the exact same, when they are new.

/Ubbe
 

Rawkee1

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I think I'm leaning towards the Diamond F23H. I'll have to cut it for the 158- 160Mhz range for best results. I'm not sure where the cut has to be made but I believe it will explain in the instructions. As to putting and amplifier up there, I have the power source but I don't think the Moonraker M100 is a good choice.
 

Ubbe

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but I don't think the Moonraker M100 is a good choice.
They never say anything about its specs, no IP3 or P1 or noise figures. It usually means that they are too bad to be used in advertising.

Put the amplifier in a suitable box, the one I link to here seems to have the necessary coil from the coax to the power input to make use of a bias-T, and then a bias-T, which is only a coil and a capacitor, to power the coax. Then you'll need a suitable attenuator to set a proper signal level to the receiver. I would use RG6 coax with twist on connectors that can be reused between coaxes and then adapters or pigtails with connectors to suit the different connection points. I would add a CATV splitter with as many outputs as necessary that will also isolate between receivers and coax.

Ultra Low Noise Amplifier PGA-103+ 2 GHz; Unconditionally Stable; Gain – GPIO LABS

USB Bias Tee Operates from 10MHz - 7000MHz – GPIO LABS

Variable Attenuator F-Type 0-20dB 5-2400MHz DC Pass Metal Housing | eBay

AIM 11-4120 TV CATV 2-Way 'F' Splitter 5~900MHz 20 db Isolation ***NEW*** | eBay

/Ubbe
 

Rawkee1

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Thanks so much for this very useful information. I ca't wait to get everything in place. I'm sure it will work really well. I've read that instructions come with the F23 to cut for certain frequencies but jumping the gun here, is it cut from the top?
 

prcguy

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You take the antenna apart and cut each of the three elements separately.



Thanks so much for this very useful information. I ca't wait to get everything in place. I'm sure it will work really well. I've read that instructions come with the F23 to cut for certain frequencies but jumping the gun here, is it cut from the top?
 

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Rawkee1

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Is there any rule of thumb as to where to install a preamp on the coax cable? I;m bringing two cables into a splitter on the roof. Where is the best spot to install the preamp. Can it be installed 5', 10', 20' ect down the line? Obviously down from the splitter but how far? Is there advantages or disadvantages?
 

prcguy

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The more feedline and other losses you have in front of the preamp will degrade the system noise figure by that much more. What are you bringing together with a splitter? Combining two antennas with a splitter will give you at least 3dB loss or half your signal unless the two antennas are identical and on the same band and spaced just right apart and you have exact equal lengths of cable from each antenna to the splitter.

Is there any rule of thumb as to where to install a preamp on the coax cable? I;m bringing two cables into a splitter on the roof. Where is the best spot to install the preamp. Can it be installed 5', 10', 20' ect down the line? Obviously down from the splitter but how far? Is there advantages or disadvantages?
 

prcguy

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If you use a splitter or power combiner to combine a VHF and UHF antenna you will loose at least 3dB of the signal from each antenna in the process. The signal level will be reduced and you can't get it back by any means, especially with a preamp. You want to use a diplexer which will combine them with very low loss, usually under .5dB.

I was going to combine a VHF and a UHF antenna together. and it wasn't a preamp, it was this low noise amp I was looking into. Ultra Low Noise Amplifier PGA-103+ 2 GHz; Unconditionally Stable; Gain – GPIO LABS
 

prcguy

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I would personally never run a preamp from USB power, the 5V power supplied by a computer and most wall power supplies are very dirty and there is a good chance that will be transferred into the preamp and show up in your receiver. Also that preamp without any band pass filtering ahead if it has a good chance of overloading in your area creating lots of IMD inside the preamp which will show up as a higher noise floor and ghost signals across the bands.

That preamp should be ok if you can filter the VHF side to a range of 118 to 174MHz and UHF to 406-470MHz if you have UHF TV channels 14 through 21 in your area. If there are no TV channels within that range and there is T band communications you could allow the filter to go to 512MHz.

The best way to design something like this is a band pass filter on each antenna then a separate preamp for each band then combine after the preamps. That will reduce the amount of signals into the preamps further protecting them from overload.

I was going to combine a VHF and a UHF antenna together. and it wasn't a preamp, it was this low noise amp I was looking into. Ultra Low Noise Amplifier PGA-103+ 2 GHz; Unconditionally Stable; Gain – GPIO LABS
 

Ubbe

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I was going to combine a VHF and a UHF antenna together.
Maybe you can use a $30 diplexer like the one in the link below, that have practically zero attenuation in the passbands. Having one amplifier between diplexer and the coax down to scanners are probably fine. But I would install a second RG6, one to each antenna and connect to different scanners, if you have several. I see big differencies in signal depending of where the antenna are located and UHF can sometimes be received better from the VHF antenna than the UHF one, but that is when I have no line of sight and only receive reflections. Diplexer 2m 70cm 50W for Ham Transceiver | eBay
The diplexer will stop the antennas from interfering with each other, which they will do if just connected together.

If you have mains power outlets in the attic you can power the amplifier directly from a USB power adapter. If you suspect interference from the power adaptor then use a power bank and compare if there's any improvement. I don't see any interference from my cheap chinese USB chargers but there are probably some out there that do.

That PGA103+ amplifier have much better performance than any scanner and in most cases do not need additional filters, but your scanners might need them. Just see to that you do not have a too big signal and attenuate enough to not overload the scanner. That's the mistake most people do and then rejects amplifiers as they only make things worse and amplify noise. But that's not true. Almost any amplifier will improve reception if the signal level are set properly.

/Ubbe
 

Rawkee1

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Thanks so much guys for your highly technical input. My question is that why don't these scanner companies make the scanners with different inputs for VHF- UHF- 800Mhz? I believe I had an old Regency with separate vhf/uhf inputs many years ago. The plugs were the old push in car radio type. It would be much easier for me to run two separate antenna lines than to be adding all the appliances to make them work right. I'm glad I conversed with you two because I would have just used a TV splitter. I looked at that diplexer on line and it is in Hungary. I'm hoping I can find one closer to home here. If I already have two lines to the scanner, can I put the diplexer before the scanner without the coax at equal lengths or should the diplexer go closer to the antennas?? Just looked and that diplexer on Ebay ended. Where can I get a a good low loss diplexer? Soo much has changed from when I was doing this scanner listening 40 years ago.
 

prcguy

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Are you combining a VHF and UHF antenna or is there 800 in the mix?

Thanks so much guys for your highly technical input. My question is that why don't these scanner companies make the scanners with different inputs for VHF- UHF- 800Mhz? I believe I had an old Regency with separate vhf/uhf inputs many years ago. The plugs were the old push in car radio type. It would be much easier for me to run two separate antenna lines than to be adding all the appliances to make them work right. I'm glad I conversed with you two because I would have just used a TV splitter. I looked at that diplexer on line and it is in Hungary. I'm hoping I can find one closer to home here. If I already have two lines to the scanner, can I put the diplexer before the scanner without the coax at equal lengths or should the diplexer go closer to the antennas?? Just looked and that diplexer on Ebay ended. Where can I get a a good low loss diplexer? Soo much has changed from when I was doing this scanner listening 40 years ago.
 

Rawkee1

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I guess your right nd5y and it makes much more sense to run one cable. I get it, but if not using the correct splitters, diplexers, cable ect than your just wasting your time by not getting the receiving results that you should. To answer your question prcguy, 800mhz not a big deal. I for the most part lock out MSP & Worcester that are all on that state 800 thing. I occasionally listen to state with no problem. Worc little garbled with their voices, but I worked for the city and even their own radios were a little garbled. Isn't it better to have one antenna for vhf tuned to 158-162 that I listen to and one antenna for 460-470 that I listen to as well? Or just cut A Diamond F23H to the VHF 158-162 and hope for the best on UHF?
 

Ubbe

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My question is that why don't these scanner companies make the scanners with different inputs for VHF- UHF- 800Mhz?
I've suggested that to Uniden. It justs a couple of more $0.05 diodes and additional antenna connectors. Then there should be a setting in the scanner, very much like the filters in SDS scanners, that selects which antenna to use for a department or site, or set to global. If all are set to the same antenna then it works as it do now, using one antenna for everything. Even a discone antenna can not handle the whole frequency range that scanners use.

I guess the USB port would be quick enough to make it possible to use an external antenna switch box and only the firmware needs a change to send control commands to the box that would have 4 antenna ports. Then that box would work with all scanners that had a compatible firmware and a USB port and doesn't need any hardware changes.

/Ubbe
 
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