reconrider8
Member
ok i have a rs antenna but it doesnt pick up 800 band very well so i was wondering if i get a T and hook up an 800 mhz antenna would it work with both and help my 800 any
Multi antennas
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KC0QNB
Member
T no splitter maybe.
First look at the sticky at the beginning of this thread on using multiple antennas with one scanner.
http://www.radioreference.com/forums/showthread.php?t=113057
Dave
http://www.radioreference.com/forums/showthread.php?t=113057
Dave
reconrider8
Member
what would be the splitter to get i have a bct-15 and the rs antenna and i want to get the rs 800mhz
KC0QNB
Member
Something like this might work, I don't use one but there are others on here that do.
http://www.scannermaster.com/SP_1300_Combiner_Splitter_p/24-531025.htm
http://www.scannermaster.com/SP_1300_Combiner_Splitter_p/24-531025.htm
jim202
Member
Not wanting to start a war on who is right and who is wrong, the bottom line is that if your only
going to use the antenna for receiving, it really doesn't matter. the mis-match from hooking
two 50 Ohm antennas together only makes it look like a 25 Ohm antenna match. On receive,
this isn't that bad. The frequency band of say VHF and 800 or VHF, UHF and 800 will work
for a scanner antenna.
Now if your asking to transmit on this kluged antenna system, this is a whole different matter.
Don't do it. Go for a triplexer and get the correct match. There are a couple of companies
that make such a unit. Have used them a number of times on mobile command centers
where we have run out of cables going to the roof. You then install a tri band antenna
and use the triplexer to split the antenna to 3 different radios. The triplexer has band pass
filters in it to allow just the range of frequencies they are made for to pass.
Sometimes you just have to buck the normal and go with what us old time communication
engineers have to work with. If you haven't been there and done that, then how can they
say not to do it this way or that way. Any way, go for it and have fun with your scanner.
Jim
going to use the antenna for receiving, it really doesn't matter. the mis-match from hooking
two 50 Ohm antennas together only makes it look like a 25 Ohm antenna match. On receive,
this isn't that bad. The frequency band of say VHF and 800 or VHF, UHF and 800 will work
for a scanner antenna.
Now if your asking to transmit on this kluged antenna system, this is a whole different matter.
Don't do it. Go for a triplexer and get the correct match. There are a couple of companies
that make such a unit. Have used them a number of times on mobile command centers
where we have run out of cables going to the roof. You then install a tri band antenna
and use the triplexer to split the antenna to 3 different radios. The triplexer has band pass
filters in it to allow just the range of frequencies they are made for to pass.
Sometimes you just have to buck the normal and go with what us old time communication
engineers have to work with. If you haven't been there and done that, then how can they
say not to do it this way or that way. Any way, go for it and have fun with your scanner.
Jim
prcguy
Member
There is way more to the problem of combining two antennas with a T adapter than just the impedance mismatch. Using a VHF and 800 antenna combined this way as an example, the VHF antenna will pick up some 800 and depending on the specific lengths of cables from the T to each antenna, the signals from both antennas can arrive out of phase at the T and nearly cancel each other out. Bottom line in this case is potentially good signal at the antenna but not much at the receiver. Using a splitter (combiner) of the correct impedance is also not the right way because each antenna will incur a minimum of 3dB loss from the splitter and you still have the potential of signals combining out of phase and canceling. The correct way is to isolate each antenna with a band pass or high/low pass filter to prevent signals from one antenna to combine with the same band signals from the other antenna and this is what a diplexer or triplexer does.
prcguy
prcguy
You gotta love the misinformation that gets spread in these forums. Read the sticky's. prcguy is correct - it's WAY more complicated than a simple impedance matching problem. It's easily solved with a properly designed diplexer or a better performing broadband antenna.
Take a look here http://www.rfparts.com/diamond/Product_Catalog/plexers.html and see what duplexer or triplexer will cover the ranges you want to monitor. You would have to use some adapters at some point to match up your connectors, but you can see these devices give you some flexibility for properly matching multiple antennas. And agree with Prcguy, you would very likely have some signal phase cancellation problems just using a combiner. If you're gonna do it, do it up right.
reconrider8
Member
this is the one i want to add http://www.radioshack.com/product/i...er/HAM&allCount=24&parentPage=family this is the one i got http://www.radioshack.com/product/i...er/HAM&allCount=24&parentPage=family i didnt see ant duplexer that really covered what i needed
If a standard one will not meet your needs then custom diplexers based on Model LH7 can be bought from Tin Lee Electronics here:
http://www.tinlee.com/Diplexer-Custom.php?active=1
Dave
Thats just it, you haven't really specified to us what freq ranges you want to cover. You have mentioned 800, but not if you are monitoring both VHF and UHF also. Did you look at the triplexers? Some of them extend up high enough. You don't have to use all the ports if you don't need them. But if you would specify the ranges you want, we might be able to tailor our advice.
reconrider8
Member
o ok i mainly cover police, fire, ems, rescue, mil air, some ham, ect so the range would prob be like 130-350 on the one i have but i wouldnt mind covering some of all the ranges if i could just get what i have to work with the other i would be happy i scan all i can pick up not just one constant range
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Well, you can't really cover "it all" efficiently without several antennas cut to specific ranges. There are many antennas that supposedly cover from here to there (i.e., 25 to 1300 Mhz). And yes they can receive across that range, but not effectively all the way through. Anytime you try to cover such a broad range with one antenna, you have to accept compromise.
As for a diplexer, since you want a broad range, you may have to go to with something like the Tin Lee products as suggested since they can do customizable designs. Buying a diplexer or triplexer off the shelf will likely give you gaps in coverage. Basically though, all of us work with some compromise. It is just a factor of how much you can live with. I often use a VHF/UHF antenna at home, but still listen to my county 800 Mhz trunked system. Since it is close enough there is no degradation in reception.
Anyway, hope some of this helps in understanding your situation. Happy listening....
As for a diplexer, since you want a broad range, you may have to go to with something like the Tin Lee products as suggested since they can do customizable designs. Buying a diplexer or triplexer off the shelf will likely give you gaps in coverage. Basically though, all of us work with some compromise. It is just a factor of how much you can live with. I often use a VHF/UHF antenna at home, but still listen to my county 800 Mhz trunked system. Since it is close enough there is no degradation in reception.
Anyway, hope some of this helps in understanding your situation. Happy listening....
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