Running one scanner with multiple antennas

[benbenrf]

kpoe_28

If the signals are strong enough chances are you'll suffer little real world signal loss, but for weak signals and those that are boarderline, you'll start to suffer the effects of the messed up effective impendence – especialy the case when the combined antenna's are of different types with different gain and current distrabution characteristics (e.g. when combining a directional antenna with an omni-directional antenna).

Best do the job properly – something along the lines of a Mini Circuits ZFSCJ-2-1, or similar – or maybe check out eBay. Theres a good quality 3-way splitter/combiner going for 50 bucks (Item number 350124822928), and a 4 way (you may want to add addition antennas later!) going for around 50 bucks (Item number 160437475598)

Even better: a coaxial switch – type into ebay “HP coaxial switch” in the All Catorgories section, and this evening, at least, around 120 HP coaxial switches came up. That HP gear is top class professional hardware going for a fraction of what it costs new.

A coaxial switches are great - with a small rotary switch on your desk, you can now select whichever antenna you wish to use, use both at the same time, or disconnect both (from your receiver) when there's lightening about.

They run off dc voltage and you'll be able find wiring diagrams for them on the net just "Google" the HP part number for the data/spec sheet. If you do choose one and it's not IP sealed for outdoor use, invest in a weather proof box to mount it in. Stick it up on the mast, and use exact equal lengths of coax between each antenna and the switch (or combiner).

PS - if you type in just "coaxial switch" there are some 500 odd choices to look at!!

 

[ScanWI]

High Gain 800Mhz

My question would be is it just easier to put a antenna switcher between then mount both the wide band receive and a dedicated 800Mhz? This is for in MN where I'll either be listening to VHF or 800 very rarely both and the wide band can cover that.

 

[GarudDog]

Good idea and bad idea

Not a bad idea.By having two raidos with one antenna.I have try that befor and it did not work.I have try it with a cb and a scanner antenna and it would not work.And i have try it with a sacnner antenna to a cb.And that would not work to.The problems was.When you go to talk on the cb.The sacnner would not pick up the raido frequencys.Why is that.You are taking a way the power from the antenna form picking them up..I have ben lookn for a filter for that.And at this time i'm being told that there is no filter out there for this.If some one do fine one.Let me know asp os i can get one of them.You can get me at Guard-Dog@live com.And kept on trying.My be one day some one will get luck e for us.GuardDog.

 

[ScanWI]

Not a bad idea.By having two raidos with one antenna.I have try that befor and it did not work.I have try it with a cb and a scanner antenna and it would not work.And i have try it with a sacnner antenna to a cb.And that would not work to.The problems was.When you go to talk on the cb.The sacnner would not pick up the raido frequencys.Why is that.You are taking a way the power from the antenna form picking them up..I have ben lookn for a filter for that.And at this time i'm being told that there is no filter out there for this.If some one do fine one.Let me know asp os i can get one of them.You can get me at Guard-Dog@live com.And kept on trying.My be one day some one will get luck e for us.GuardDog.

If you have two transmitting radios hooked to the same antenna and transmit you will wreck the other radio it is different if you have two receive only radios hooked up.

 

[Baylink]

Ok.

I was a good boy. I saw the sticky, and I read all 44 replies.

But I still don't have an answer to my question, which is: how, precisely, do you go about providing receive antenna(s) for receivers like the AOR 8200, which are good from DC to light?

Ok, 50kHz to 3GHz, but for our purposes here, it's the same thing.

People have been posting suggestions to use diplexers... which, to my understanding, are devices intended to keep *transmitters* from screwing with other transmitters, and other receivers, connected to the same feedline, from the *bottom*.

What, precisely, is the problem with connecting, say, 2 separate discones, optimized for different ends of the spectrum, to the same coax? Solely impedance matching? Is a combiner -- akin to the splitter you would use for, say, attaching multiple satellite receivers to the same LNB -- sufficient to solve that problem, and is that the only problem you'd need to solve?

I inferred from Lindsay's original posting that the problem I'm trying to solve (or the related "add a beam for this one system" problem) is the most common problem people are trying to solve.

But none of the replies I read seemed to clearly address it.

Is it just me? So many things are just me.

 

[caleb1301]

I have 2 Radio Shack Thru-Glass scanner antennas. One on my truck and one on my car. If i were to take the one off my car and put it on my truck, and couple it with the other thru-glass antenna to my scanner, would help strengthen the incoming signals? or would it just be useless? im not having any problems receiving, i was just wondering is all.

Thanks,
Caleb 1301

 

[OemUser]

Amazing....the depth of available knowledge...

Thank you, folks....you saved me from myself, again. I have 4 spare identical Diamond discones looking for something to do.

Falling into the more is better trap again, I had wondered about mounting them at some equidistant point from each other, and feeding them to one receiver.....my thought was that because they were identical, I would have more "capture area", if that makes sense....

I realized that there would be feedline impedance issues to overcome; what I hadn't considered was the "signal phasing...or time of arrival of the signal"...compared to the other 3 discones...and completely forgot about the array effect....

Anyway, thanks for the info....back to the drawing board...

 

[PCTEK]

ok, with all of this talk about multiple antenna's and diplexers, how does the ANT-135 from Scanner World work? I have one and it seems to pickup all but my 800Mhz signals. Are you saying that of the 3 antenna's on the ANT-135, only 1 is really working?

I was going to replace one of the antenna's with an 800Mhz specific antenna, but from what I'm reading here, that won't work???

 

[W6KRU]

ok, with all of this talk about multiple antenna's and diplexers, how does the ANT-135 from Scanner World work? I have one and it seems to pickup all but my 800Mhz signals. Are you saying that of the 3 antenna's on the ANT-135, only 1 is really working?

I was going to replace one of the antenna's with an 800Mhz specific antenna, but from what I'm reading here, that won't work???

In my opinion that is not three antennas. It is one antenna with three elements. There is a difference. Shortening one of the elements might help with 800 but I doubt it and it would more than likely hurt performance on other bands.

Here is a link to the antenna in question in case anyone else is curious.

ANT135BNC, INDOOR BASE OR MOBILE ALL BAND SCANNER ANTENNA, WITH BNC CONNECTOR - Scanner World - The Largest Dealer of Scanning Radios in the World

 

[domu]

Need help with combining two antennas

I figured that posting to this thread will do but please correct me
if my assumption is wrong.

I need to combine output from two antennas to send it down
through approx. 50m single coax run to feed two receivers.
ANTENNA 1 is for 1040-1090 (Mode2/ADS-B), ANTENNA 2 is
for 118-136 (Airband). I am aware that combining input from two
antennas may be challenging, but since those antennas are
dedicated for their respective bands - I speculate that it wouldn't
be a source of major problems. And just to stay safe I would add
bandpass filter ~1050 on the output from ANTENNA1.
I understand that 50m coax run plus combiner and splitter will
introduce significant loses to the signal, hence I would add
masthead amplifiers for both antennas.

Below is ASCII diagram of what I hope would work:

                                                            /-- POWER
ANT1 --B/P FILTER--M/H AMP --\                             /-- RCVR1
                              COMBINER---COAX50m---SPLITTER
ANT2 ------------> M/H AMP --/                             \-- RCVR2

I do not have any expertise in this field, this is one time
project, and I doubt if I ever will return to this subject
again. Just need to solve the problem, and want to do it as
good as possible. Therefore, I have a couple of questions:

- would it work ?

- is there a better solution ? (must be single coax)

- what coax could I use (RG-8/U,RG213,LM400,CNT400,9914F) ?

- what amp/splitter/combiner would you recommend ?

- does it matter how those two antennas are far apart ?

- what products of your company would let me accomplish above
(please list/quote)


Thank you for any helpful answers

 

[JimBobTerp]

Hi
I was wondering if there is a way to hook up a Base Model HAM RADIO to this antenna?? WBD-40 Discone Base Antenna the reason I asked is cause I have already planning on hooking my Police Scanner to this antenna also with the coax cable i got. So can some one help me and if so give me a step by step way to do it. thanks!

 

[Daniel_Boone]

I'm not sure that I am not too late to post a comment in this forum - but the only problem I see with what you are trying to do is the fact that as you make the antenna more directional - to increase forward gain - you loose some reception off the back side of the antenna.

The answer - if no one else thought of it - I don't know because I only read the first page - but the answer is to use a good all band television antenna. The VHF will pick up those ranges and the UHF YAGI will pick up the upper bands.
You would need to use some type of mast head pre amplifier such as the Channel Master CM 7777 - with the FM trap closed - because you want to amplify the radio ranges but not the wide bands of FM radio 88 - 108 mhz or there about's.

The problem with trying to receive those ranges with any other antenna would be the harmonic's of a antenna that is not the proper length.
A regular television antenna such as the Winegard 8200U = works on a very basic principal where the antenna changes its length electrically - by looking up and down the array to make it appear to the signal as being the same size as what you need to receive the VHF frequencies - which are the hardest to receive.
The UHF - as we all know - the directors and elements are parasitic - the only ones that are physically connected to the feed line is the driven element .. So as long as you use a real good sweep tested coax such as the Belden 1829 AC and some sort of preamp to compensate for line loss - the possibilities are unlimited as long as you can get as much height as possible and as long as you aim it in the direction you wish to receive in.

Hope this helps - and if anyone needs anymore information - just send a PM and I will be happy to explain it to you.

I wouldn't want to combine two signals from two different antenna's and then try to split it two ways - due to the fact that Duplexers are very inefficient and they throw away half of the signal in the duplexer. Combine then and then try to separate them and then try to split them and in the end - all you are going to have is a bunch of noise.

 

[glennradio]

One scanner with multiple antennas

Just a thought for anyone to ponder. I have both an amateur radio station and a scanning station. I use two Ameritron RCS-8V remote coax switch boxes (one for each station). I have an antenna farm with about a dozen antennas covering 2 Mhz through to 1090 Mhz. Each box takes connections from 5 external antennas and runs one cable into my basement from each box.
I select for my scanning station the antenna I desire by simply rotating a selector knob. Because my scanner station is receive only, I have moved to using RG-6 satellite cable rated for 3.5 gigahertz and F adaptors where needed. My fumbling around in the beginning was to work out a problem receiving a signal on my Air Nav Radar Box so after spending countless hours using various coax like RG213, RG8, LMR400 etc ...... I took my modified Midland antenna that I had for the 1090 Mhz signal I needed, and fed it from the antenna to my basement with the satellite cable and was stunned to find how well the result turned out to be. The cable run is about 60 feet in total with the antenna up around 28 feet in height. Getting that positive result on such a high frequency has convinced me to stay with the satellite cable for my scanner feed from the various antennas I use which consist of directional yagi's pointing toward a specific city, to discone antennas for wideband use or specific frequency antennas for monitoring or scanning for a specific agency. I hope this info helps others if they have run out of ideas. Check out the remote switch on the internet and the reviews on eham.net.

 

[Little_Spike]

I been providing the railroad radio stream for Pottstown, PA. on the Railroadradio.net and also on here for Chester County.
I have two antenna's hook togther to act as one. it works well. I have a All Band Scanner antenna cut to the RR band 160 - 161 MHZ. and a Hy Gain 130 - 225 Mhz. both antennas are around 30 ' in the air.

Coax is RG58/U.

Len.

 

[zz0468]

I been providing the railroad radio stream for Pottstown, PA. on the Railroadradio.net and also on here for Chester County.
I have two antenna's hook togther to act as one. it works well. I have a All Band Scanner antenna cut to the RR band 160 - 161 MHZ. and a Hy Gain 130 - 225 Mhz. both antennas are around 30 ' in the air.

You THINK it works well. But chances are very good that there is some deep nulls in the pattern that you're not aware of. It IS possible to combine antennas that way, but it requires careful calculation of the phasing harness, and physical positioning of the antennas. Anything else will produce random results. It'll work really good in some directions, and really bad in others. But so long as signals are in saturation and full quieting, the typical scanner user has no way of knowing just how bad it is.

Coax is RG58/U.

How long?

 

[davidmc36]

Still looking for a good 800 MHz performer if anyone has any recommendations. Or would an 800-only antenna still receive nearby VHF-Hi decently????

I do exactly that sometimes in my workshop. Take the 396 there with a very nice 800 antenna that I use and it pulls in the VHF from nearby quite well. (3 or 4 out of 5 with almost no static.

 

[davidmc36]

You THINK it works well.......... But so long as signals are in saturation and full quieting, the typical scanner user has no way of knowing just how bad it is.

I messed around with a couple configurations and unless I was "right on top" of the transmitter, it always caused some level of background noise. VHF and 800 really did not play together well. I ended up with a nice multi-band groundplane that has 800 UHF and VHF radials on it. Not my creation, a well proven antenna design. Funny enough the multi-band's weakest was UHF so I just put up another antenna for UHF and use separate scanners.

Too bad the rail feeds are down right now or I would have a listen. Will they be up later today Spike?

 

[Little_Spike]

You THINK it works well. But chances are very good that there is some deep nulls in the pattern that you're not aware of. It IS possible to combine antennas that way, but it requires careful calculation of the phasing harness, and physical positioning of the antennas. Anything else will produce random results. It'll work really good in some directions, and really bad in others. But so long as signals are in saturation and full quieting, the typical scanner user has no way of knowing just how bad it is.



How long?

I been in radio for close to 30 years. I'm sure I know how to hook two antennas together so they act as one.
The coax altogether is about 100' long.

The SWR's are very good. I checked them with the meter and my friends ham rig.

Both antennas and Coax are grounded aswell as the Radio.

Len.

 

[zz0468]

I been in radio for close to 30 years. I'm sure I know how to hook two antennas together so they act as one.

Can you define what you mean by "acting as one"?

For example, a pair of vertical dipoles spaced 1/4 wave apart and fed 90 deg out of phase will create an end-fire pattern with a deep null off the back. Space those same dipoles 1/2 wave and feed them in phase and you get a figure-eight pattern with two deep nulls, and two lobes with 3.8 db of gain. You can also stack the dipoles to reduce vertical radiation and provide some gain at low radiation angles.

In all cases, it's essentially "two antennas acting as one". But to get the desired results, the separation is critical, and the length and impedance of the phasing cables is critical. And if any of those details are neglected, you will get random results. Period.

The coax altogether is about 100' long.

Of RG58!? 5.8 DB loss at 160 MHz...

The SWR's are very good. I checked them with the meter and my friends ham rig.

Of course the SWR is good. With 5.8 db loss out, and 5.8 DB loss back, a dead short would have a return loss of 11.6db, or a VSWR of 1.7 to 1. The coax is essentially acting like a dummy load. A very mediocre antenna match would look great, so far as a VSWR meter is concerned, but the reality is, you'd be losing 75% of your signal in the coax IF (and that's a big if) the antenna is a perfect match to the coax.

Both antennas and Coax are grounded aswell as the Radio.

Good. At least it's a safe installation.

 

[tomasG]

I'm not sure what to comment on first.

Hmm... to combine one antenna to two non-transmitting radios one may use a simple, cheap, cable TV splitter. Awesome performance. Or spend $200 at Stridsberg and get a multicoupler. The passive multicoupler may also be used as a combiner that combines multiple antennas to one output but it is not the best performance. Combining antennas isn't as simple as just using a T.

The proper way is to use a diplexer or triplexer. I use a Diamond MX2000 and it separates out 1.6-60/110-170/300-950. This lets me use and old CB antenna for CHP - killer performance. I then use a 2 meter antenna for VHF and it covers airband up to forest service reasonably well. Then I use a 440 amateur antenna for UHF. I do fine. I've also used a Tram dual band 9dB gain (the same as a Comet GP-9) for VHF/UHF and it kicks butt. No combiner/diplxer/yada-yada-yada needed.

The purpose of the triplexer is to place tuned circuits inline that allow the laws of physics to select the antenna for the scanner. The path of least resistance and all that. Ijust ordereda Ferret and I know that it won't work nearly as well as this setup, but I moved and cannot have all the anetnnas like at my Dad's house. The triplexer bewing tuned circuits also cuys down front-end overload that sounds like intermod.

If you want to transmit on a CB radio while listening to a scanner on the same antenna -- umm, nope. In commercial two-way a true combiner may be used with a duplexer but usually we use split antennas and combiners. But not on multiple bands.

Somehow this thread got really complicated and went in different directions. Keep it simple.