Posted: 5/16/2017 1:01:40 PM EDT
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First off, hello, all. This is my first post in this section. It's not even really a ham question, but I'm sure there's a few here who can answer it.
I have a Comet X50A up on my roof for my UHF/VHF rig. It's mounted about 35' above grade and performs well for its intended purpose. Here's the question, how will it do as a wide band antenna for a scanner? I've recently invested in a Uniden BCD436hp with the intent of monitoring some of the emergency channels in my area. Problem is the shack is in my basement so I'm not expecting stellar reception while at home without an external antenna. I'm trying to decide whether to mount a separate antenna for the scanner or just put in a switch and share the antenna between the scanner and the UHF/VHF rig- one at a time, of course. Seems to me it should work well for everything in my area but 800mhz, the question is how much will it suck on 800? I don't really want to purchase and mount another antenna, but if I have to, I have to. Thanks for any input. |
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The antenna you have up won't work very well for a scanner. It is tuned for the specific frequencies it was built for. As you get further away from those frequencies the signal will have to be stronger to pickup up. There will be some harmonic frequencies that will come in okay. I would recommend a wide band scanner antenna sometimes also called a discone.
Go here and search for discone http://www.hamradio.com/search.cfm |
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The antenna I have should work decently at the 150.000-158.000 and 450.00-470.000 ranges that a lot of the emergency broadcasts in my area use, probably better than a discone.
If I'm wrong about that, please let me know, I'm a newbie at all of this. Beyond that, I'm just wondering if it's going fall completely on its face in the 800 range. |
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I have no idea what it will do on 800, but it will kick the snot out of a discone for VHF and UHF.
Keep in mind that your public safety 800 system is designed (probably) to support some guy with an HT in his car, the proverbial "wet noodle" antenna, so probably won't take a lot to receive it. Only way to know is to try it, pretty trivial to plug it in and see what it does, then decide if you want something else. |
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You will need an antenna analyzer capable of covering the bands you are trying to monitor with the scanner, to check the antenna performance.
There is one easy way to find out. Hook it up to your scanner and try using it. It may do well for that your are trying to listen to. Be careful with the antenna switches. Some switches may not provide enough RF isolation due to some capacitive RF coupling inside the switch. All quality antenna switches will ground all outlets not being used. This may not be enough on the VHF/UHF bands. I use a "Discone" antenna from Radio Shack for a scanner. I bought it for $1.68, at 95% off when the store was closing. It works great with a low-loss RG-6 cable that I got for free from a cable TV guy. It's a 75 Ohm cable but a slight mismatch is virtually undetectable. Same cable is used for my 220 Mhz antenna with great results. |
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It will work fine. While I run a separate discone, I often use my 2/70cm base antenna for the scanner as well.
I've confirmed using my RTL-SDR that the signal strength impact isn't significant when it comes to picking up the trunking channels. If I were trying to listen to 800 MHz mobile directly, I'd prefer to have an antenna specifically for that, but the comment above it correct -- the trunking system in my area runs 300W out on multiple mountaintops, anything is going to work for it. There's so much signal coming in I've been able to run it into a 3-way CATV signal splitter and feed both the uniden scanner and two RTL-SDRs without any impact in reception. Feedline attenuation is probably the bigger deal, and again, there's enough power to fix that as well. |
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Thank you all for the input. Sounds like I'll probably be okay with the existing antenna. Radio doesn't arrive until tomorrow and it looks like I'm going to have to order an adapter so it'll be a few days until I can try it, but based on posts here I am optimistic.
If and when I confirm it works acceptably, I'll look into sourcing a quality switch. Knowing me I'll have a dedicated antenna up there sooner or later but it's nice to know I probably have a decent interim solution. |
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Quoted:
I'll look into sourcing a quality switch. Knowing me I'll have a dedicated antenna up there sooner or later but it's nice to know I probably have a decent interim solution. |
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The vast majority of switches will not give you enough isolation from the scanner when you are transmitting. You will need to disconnect the scanner when transmitting. So far the switch worked well but I would not use it for VHF/UHF, even at low power. OP, you best bet will be to install a female connector on the antenna side and manually plug the extension coax cables into it. You can buy quick lugs too. So far the best antenna switches I was able to find were made for military applications, with coaxial "reed" switches inside. A relatively small switch could handle 3 kW with no issues. "Reed" type vacuum relays are a great choice for a high power, home brew HF antenna switch. VHF/UHF is a bit more complicated but can be done. |
| Thanks for the heads up on the switches. I was leaning that way because the back of the UHF/VFH rig isn't all that easy to access. I guess I can just run a jumper to the transceiver and swap the antenna connection back and forth I'm going have to disconnect it, anyway. |
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I have a qtr wave dual band VHF/ UHF Ham antenna meant for a car that I put a radial kit on.
I put it in the attic and it picks up local cop cars and fire trucks in the 800 mhz freqs many towns away, about 50 miles. I was listening to security on it for an event in Boston over 60 air mikes away. It will work just fine, much better than the antenna the scanner came with. |
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Quoted:
I have a qtr wave dual band VHF/ UHF Ham antenna meant for a car that I put a radial kit on. I put it in the attic and it picks up local cop cars and fire trucks in the 800 mhz freqs many towns away, about 50 miles. I was listening to security on it for an event in Boston over 60 air mikes away. It will work just fine, much better than the antenna the scanner came with. |
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Got it hooked up and it works great. This is my first scanner experience so,I have nothing to compare it to, but I'm picking up stuff in the 700-800mhz from 40-50 miles away nice and clear. Even the little Diamond SRH77CA I picked up does okay inside the house, I'll be trying it mobile tomorrow.
The bigger problem was programming this damn thing. That's a work still in progress...I have it up and running but it needs some serious tweaking. |
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Were you hearing the cars directly or the repeater they use? Quoted:
Quoted:
I have a qtr wave dual band VHF/ UHF Ham antenna meant for a car that I put a radial kit on. I put it in the attic and it picks up local cop cars and fire trucks in the 800 mhz freqs many towns away, about 50 miles. I was listening to security on it for an event in Boston over 60 air mikes away. It will work just fine, much better than the antenna the scanner came with. |
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Your dual band antenna will probably work better than the standard little shortie over the frequency range of the scanner, and should at least get you all of your local stuff. The discone might work a little better on some frequencies and not as well on others but the major factor in receiving VHF/UHF strong signal modes such as FM is that there is a path (i.e. a line of sight from transmitter to receiver so in the case of a scanner antenna, illuminating a certain radius around your location). So height above ground is key.
Of course a certain amount of energy has to reach the antenna terminals of your receiver for there to be a useable signal and other factors such as line loss and antenna gain at a particular frequency, distance from the transmitter, and receiver sensitivity itself can affect that, but the first rule is proper antenna placement to establish a path. This is put very simply and doesn't consider all of the reasons certain antenna performance characteristics are chosen for particular applications. With a scanner your targets will most likely be other base stations or repeaters and they will be doing most of the work because they are already designed to communicate with mobiles and HTs with smaller, lower gain antennas (as was already mentioned upthread I think). |
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Old school ham here from back in the hollow state days when radios glowed in the dark.  |
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For a scanner or wideband I would pick up a discone.. TX 144 - 1300 MHz LINKY
I have one of these and for wideband it works great, used it with a SDRplay.. Will work for transmit but has no gain.. Cant go wrong for 50$.. If you live in the DFW area let me know and I will make you a deal you cant refuse.. Too big to ship... Prosise |