Signal Loss-Single Discone Antenna to Two Scanners

[rbritton1201]

I have a single Discone Antenna that receives 25-1300 MHz, mounted in the attic, and that setup has always received well as a scanner antenna for both analog and P25 signals.



I now have two scanners, a Uniden SDS200, and an Uniden BCD536HP, but just one RG8U mini foam coax cable running down to the shack in the basement, about 60 feet distance from the Discone antenna in the attic.

I'm running both scanners off of the one Discone antenna now by utilizing a splitter and the appropriate connectors to adapt the PL-259 on the end of the RG-8U mini foam coax that terminates in the shack from the antenna in the attic, for connection to the input side of the splitter, which has an F connector input on it.



I use an F connector to SO-239 connector adapter on the input side in order to connect the splitter to the coax run from the Discone attic antenna, and two F connectors that connect to each output side of the splitter. I 'm using about a one foot section of RG-6 cable as a jumper from the output F connectors on the splitter to PL-259s on the other end of the RG-6 cable, and they plug into each respective scanner, thereby permitting me to use one antenna for both scanners. I'm using a barrel connector to convert the PL-259s to BNC, for connection at the scanner inputs.

Some of these connectors I had in my stash, and there are probably better combos to reduce the number of connectors to adapt to what you need to adapt the splitter, and varying cables to the scanners, etc...


F Connector to SO-239, F Connector to PL-259, PL-259 Barrel Connector, and PL-259 to BNC connector.



I realize the impedance differs with respect to the RG-8U versus the one foot long RG-6U jumpers between the scanners and the splitter. I also realize that the splitter must also introduce some degree of signal loss with this arrangement, and every time you use an adapter, there are theoretical losses involved. But, I don't notice any signal degradation that is discernible to the human ear with this setup.

Does anyone know if I am theoretically incurring losses with this setup, and if so, about how much would you estimate it might be? Just curious about this setup, as it seems to work as well as if I had the scanners each plugged into dedicated antennas for each scanner.

If the losses aren't anticipated to be too excessive, if at all, it would be significantly easier and cheaper to use this setup, only one antenna, rather than having to purchase dedicated antennas for each scanner. There may even be splitters available with multiple inputs and outputs to run multiple scanners off of just one antenna, if the losses don't noticeably impede receive performance.

 

[R8000]

Yea, you will have losses.
This device will provide 4 outputs and will compensate for the losses. If you need more than 4 ports, they make a 8 port model.

Receive multicoupler

 

[rbritton1201]

I'm sure it's more efficient, it says it eliminates losses...but, the cost is pretty steep! I can't notice any difference between the splitter I'm using, which costs $9.99, when connecting up just two scanners. I assume that going to as many as four or eight scanners, you might need the better device to eliminate losses. I suppose the device linked would still be cheaper than buying four or eight antennas, plus finding the room and performing the labor involved in erecting them all.

Yea, you will have losses.
This device will provide 4 outputs and will compensate for the losses. If you need more than 4 ports, they make a 8 port model.

Receive multicoupler

 

[a417]

I'm sure it's more efficient, it says it eliminates losses...but, the cost is pretty steep! I can't notice any difference between the splitter I'm using, which costs $9.99, when connecting up just two scanners. I assume that going to as many as four or eight scanners, you might need the better device to eliminate losses. I suppose the device linked would still be cheaper than buying four or eight antennas, plus finding the room and performing the labor involved in erecting them all.

If what you have works for you, and you notice no loss...you're all set. Those recieve multicouplers pay for themselves when you have weak signals that you need split and need it split many times. If you're listening to some flamethrowers and have short signal paths and good conditions and a single split or 2, they might not be necessary, as you have seen.

 

[rbritton1201]

With the quality of stuff these days, I just hope the cheap splitter keeps working as well as it seems to now, LOL...

If what you have works for you, and you notice no loss...you're all set. Those recieve multicouplers pay for themselves when you have weak signals that you need split and need it split many times. If you're listening to some flamethrowers and have short signal paths and good conditions and a single split or 2, they might not be necessary, as you have seen.

 

[buddrousa]

I have a single Discone Antenna that receives 25-1300 MHz, mounted in the attic, and that setup has always received well as a scanner antenna for both analog and P25 signals.

View attachment 111566

I now have two scanners, a Uniden SDS200, and an Uniden BCD536HP, but just one RG8U mini foam coax cable running down to the shack in the basement, about 60 feet distance from the Discone antenna in the attic.

I'm running both scanners off of the one Discone antenna now by utilizing a splitter and the appropriate connectors to adapt the PL-259 on the end of the RG-8U mini foam coax that terminates in the shack from the antenna in the attic, for connection to the input side of the splitter, which has an F connector input on it.

View attachment 111558

I use an F connector to SO-239 connector adapter on the input side in order to connect the splitter to the coax run from the Discone attic antenna, and two F connectors that connect to each output side of the splitter. I 'm using about a one foot section of RG-6 cable as a jumper from the output F connectors on the splitter to PL-259s on the other end of the RG-6 cable, and they plug into each respective scanner, thereby permitting me to use one antenna for both scanners. I'm using a barrel connector to convert the PL-259s to BNC, for connection at the scanner inputs.

Some of these connectors I had in my stash, and there are probably better combos to reduce the number of connectors to adapt to what you need to adapt the splitter, and varying cables to the scanners, etc...


F Connector to SO-239, F Connector to PL-259, PL-259 Barrel Connector, and PL-259 to BNC connector.
View attachment 111560View attachment 111563View attachment 111567View attachment 111570


I realize the impedance differs with respect to the RG-8U versus the one foot long RG-6U jumpers between the scanners and the splitter. I also realize that the splitter must also introduce some degree of signal loss with this arrangement, and every time you use an adapter, there are theoretical losses involved. But, I don't notice any signal degradation that is discernible to the human ear with this setup.

Does anyone know if I am theoretically incurring losses with this setup, and if so, about how much would you estimate it might be? Just curious about this setup, as it seems to work as well as if I had the scanners each plugged into dedicated antennas for each scanner.

If the losses aren't anticipated to be too excessive, if at all, it would be significantly easier and cheaper to use this setup, only one antenna, rather than having to purchase dedicated antennas for each scanner. There may even be splitters available with multiple inputs and outputs to run multiple scanners off of just one antenna, if the losses don't noticeably impede receive performance.

If you had a garden hose and you put a y adapter on it do you think you would get the same amount of water at the end of each hose?

 

[GTR8000]

If you insist on sticking with a 75 ohm CATV splitter, then at least spend a few bucks and pick up an active splitter off eBay. There are a few PPC/Evolution models that will provide just enough gain to nullify the loss of splitting, usually +0.7 dB on the active ports. You can probably find a 4 port for under $20, and it will do the same job the expensive 50 ohm multicoupler will.

 

[merlin]

For receive purposes this setup should work fine. Splitting two ways you loose about half of your signal in each tap or about 3.5 Db loss. You may not notice much except for weak signals.
You could incorporate a good LNA ahead of the splitter to compensate for the losses. (this makes an active splitter of the system)
In example, I have a discone about 40 foot up. 65 foot of equal LMR600 coax into my cubbyhole.
That goes into a Scientific Atlanta 15 Db drop amp then to a splitter like yours. One tap goes to the TV, the other I switch between my scanner and SDR. This is way to hot so I put a 10 Db attenuator after the amp for about 5 Db gain. I still need bandpass filtering for nearby interference but the scanner shows full bars on everything except train voice channels 40 miles away. a noticeable improvement over the whip on the back of the scanner.
When signals seem low, then it is time to check all the connections.
Your coax is fine, you would see no difference changing to RG6. the impedance difference is insignificant.
Only reason I use LMR600 is having a couple big rolls and plenty of connectors to spare.
73s

 

[vagrant]

If you are not noticing a difference with that splitter, then stay the course. Know this though, there is a loss occurring and an experienced member on here references 3dB in his response when split between two. Alternatively, you may want to search for an Electroline 2402 (with 0dB gain) or the Electroline 2400 (with 7dB gain). They are relatively inexpensive and make sure that it includes the wall wart. It uses the same type of RG6 line with the F connector between the wall wart and the Electroline splitter. Your RG6 extension coax would plug directly into the antenna input port. I have never tried the PPC/Evolution splitter as mentioned above, but it is pretty much the same and better than just the passive splitter.

With your particular run of coax and the frequencies that discone is made for, I think the Electroline 2400 may be your best bet. The 7dB will help make up for losses, but more than 7dB can be a problem and raise your noise floor. The 2402 with 0dB is a safe bet and avoids the 3dB loss with the splitter. You should be able to find these with shipping for $50 or less. Still, if the transmitters are strong enough/nearby and you're not missing anything, don't spend another dime.

I'm sure it's more efficient, it says it eliminates losses...but, the cost is pretty steep! I can't notice any difference between the splitter I'm using, which costs $9.99, when connecting up just two scanners.

 

[thesavo]

I have a magnet mount in the attic, tied to a string of 75 ohm patch cables with barrel couplers. That is split with a 4way TV splitter. One of the output legs is connected to a 4way consumer grade distribution amp. I can't hear the loss with a radio on the first 4way and another the second one.

 

[gmclam]

An oftern overlooked aspect of an "antenna system" is the coax. Now if all you're receiving is stuff below oh say 100MHz, then you're probably good. But since a lot of stuff is on UHF these days (450, 700, 800 MHz), the quality of the coax comes greatly into the equation. Since this is for receive only, don't concern yourself over whether 50 ohm or 75 ohm, but by all means use coax that induces the lowest loss you can find/afford at the highest frequency you want to monitor.

In the end you'll have <signal from the antenna>-<loss through coax>-<accumulated loss through all connectors>-<splitter loss of at least 3dB>

 

[prcguy]

A good quality splitter will lose a tiny bit more than 50% of your signal splitting to two scanners or about 3.1dB. A TV splitter is worse loosing around 4 to 5dB or roughly 60-70% plus you will have additional loss from the impedance mismatch going from 50 ohm coax to a 75 ohm device then back to 50 ohm coax. The splitter you show in the first post is actually around a $3 part but they get marked up here and there.

You mentioned not noticing any difference using the splitter and that's because the signals you are comparing are very strong, but try tuning in a noisy signal and it will be noticeably noisier after you shove it through a TV splitter.

An active splitter designed for two way radio use like a Stridesberg works well for many people and will preserve the signal level and signal to noise ratio in most cases. You get what you pay for.

I'm sure it's more efficient, it says it eliminates losses...but, the cost is pretty steep! I can't notice any difference between the splitter I'm using, which costs $9.99, when connecting up just two scanners. I assume that going to as many as four or eight scanners, you might need the better device to eliminate losses. I suppose the device linked would still be cheaper than buying four or eight antennas, plus finding the room and performing the labor involved in erecting them all.

 

[rbritton1201]

Thanks to all for their comments, and I appreciate knowing about some of the devices recommended. With respect to my setup, I'm monitoring strong analog repeater systems that are in relative close proximity, about 2 miles as the crow flies. I live in a County that is 900 square miles, and because these agencies have repeaters, I don't miss anything, even when cars transmit from the furthest distances in the County. There is one municipality on analog, on a repeater, and they're probably about 8-10 miles as the crow flies. Their signals are perfectly readable, but a little scratchy at times. But, they're not a focus of my routine monitoring, and I actually have them VOIDED most of the time.

I'm also monitoring the State Highway Patrol, which has a P25 trunk system with various linked towers, and the furthest tower from my location is probably 20 miles away as the crow flies. I receive the furthest tower at full strength. There's a network of P25 towers that encircle my location, all of which are programmed into my scanners. So no matter where the highway patrol cars are when they transmit, I receive their signals full strength too.

So, with respect to my particular setup, I'm kind of lucky in that I don't notice any difference in reception with one scanner connected to a single antenna versus both scanners working through one antenna and the splitter.

I do have one agency located near a farm property, which is located about 60-70 miles away as the crow flies, and that system is on analog. I can receive the base station signals, but they're pretty scratchy. That system has a repeater as well, but it's really scratchy. I would probably benefit from one of the devices recommended. But, on the other hand, when I have one antenna dedicated to only one scanner when monitoring this weak signal agency, the signal quality isn't any better than when I have both scanners connected through the cheap splitter.

So, who knows, maybe a lower loss coax, and/or an active splitter, would be the wiser investment in that instance. But, that particular agency isn't much of a main focus for me, since they're so far away, and not really worth the additional investment.

 

[Ubbe]

when I have one antenna dedicated to only one scanner when monitoring this weak signal agency, the signal quality isn't any better than when I have both scanners connected through the cheap splitter.

Your SDS200 can show the signal strength in dBm. If you have a -90dBm signal connecting the coax directly to it, it will go down to something between -93dBm and -95dBm when using the splitter. But the SDS200 doesn't like strong signals and can easily degrade it's reception and loose sensitivity if there's a strong signal somewhere else in the frequency band. Then it might even help it if you attenuate the signal with that splitter and perhaps even improve reception.

There are so many variables in receiving radio signals that in some cases it's a good thing to attenuate a few dB to not overload a receiver.

/Ubbe

 

[rbritton1201]

Hello /Ubbe,

As a last resort, read the manual, right? I need to read the scanner manuals...LOL! I'm still learning their capabilities, and too lazy to actually study their range of features. I didn't realize the SDS200 displays the dBm. I'll have to check that out, and see where the signal strength is.

Your SDS200 can show the signal strength in dBm. If you have a -90dBm signal connecting the coax directly to it, it will go down to something between -93dBm and -95dBm when using the splitter. But the SDS200 doesn't like strong signals and can easily degrade it's reception and loose sensitivity if there's a strong signal somewhere else in the frequency band. Then it might even help it if you attenuate the signal with that splitter and perhaps even improve reception.

There are so many variables in receiving radio signals that in some cases it's a good thing to attenuate a few dB to not overload a receiver.

/Ubbe

 

[Ubbe]

As a last resort, read the manual, right?

It's enough to read a manual once, cover to cover. Then you'll know if something can be found in the manual. The electronic version of manuals are much easier to do searches in when you want to find the details.

I believe that you quickly can select detailed display for trunked and conventional to get the dBm value.

/Ubbe