Splitters and Such

[KK4HG]

I have a few questions about an in-house installation. Since I am now handicapped, I probably spend more time in the bedroom than anywhere else in the house. I have a GRE PSR600 and an AOR AR3000A that are currently living on my night stand. A Diamond discone antenna is hanging upside down in the corner of the bedroom (sounds squirrelly I know, but it works!). RG6 is feeding a 5-1500mHz., 2-way splitter purchased from Lowes for about $16.00 so it is a fairly decent one (so I thought). There is only about 15 ft. total of cable in use so loss is not an issue or a concern for me.

I am getting some interaction on a few AM broadcast band freqs when both radios are attached to their respective pieces of coax. In other words, a couple but not all of the AM broadcast stations I like seem to be 3+dB or more down when both radios are hooked up. If I disconnect the PSR600 from it's piece of coax, the interaction disappears.

My question is: What reasonably priced device do I need to share my antenna with these two radios and possibly a third, namely an AOR AR8200MK3 or a Kenwood TH-F6A?

Yes, I have done a search and saw info on Minicircuits and RFBay (I think) but soon became confused about a specific choice. I would like to cover as close to 3-1000mHz as possible (I realize the antenna and splitter are not designed to go that low but for my use should do fine). In fact, if someone has something for sale or trade, I would be interested.

Thanks in advance and sorry to be so long winded. I wanted to make sure that as much info as possible was shared...how did i do??!!

73

KK4HG

 

[N_Jay]

If you are trying to receive AM B-Cast (540-1700 kHz, then the discone is not the right antenna.
In your case the entire antenna wiring system is probably acting as an antenna and you almost zero isolation between receivers.

My guess is connecting the second receiver is grounding much of the wiring that is acting as an antenna.

 

[lmrtek]

What you may be experiencing is the "stub effect"

When using a splitter, any coax or device on either port tends to effect the other.

You need to use taps instead of splitters.

A tap will isolate the the equipment and coax runs from each other and eliminate any interaction.

Using taps, you can run one terminated run of RG-6 then place taps wherever you need to.

Solder Back In/Outdoor Coupler - In Line Style 16dB Loss | Blonder Tongue | 1940-16

As previously noted, a discone is not a AM broadcast antenna and actually if all your connections
are working properly, AM broadcast SHOULD be greatly attenuated since the splitter will not pass signals
below 5mhz without large attenuation and the coax shield will take care of the rest.

 

[prcguy]

A system that uses taps is usually amplified to make up for the loss in the taps, otherwise you will loose 10dB, 20dB or whatever the tap value is. There is probably no stub effect in the described problem, the jumpers would be way too short at AM broadcast to be resonant and cause any interaction. A quality splitter operated within its range should have at least 20dB isolation between output ports and unterminated or "stubed" ports would cause a small VSWR problem but that's about it.
More than likely its what N-Jay mentioned or it could be LO leakage from radio to the other causing interference.
prcguy

What you may be experiencing is the "stub effect"

When using a splitter, any coax or device on either port tends to effect the other.

You need to use taps instead of splitters.

A tap will isolate the the equipment and coax runs from each other and eliminate any interaction.

Using taps, you can run one terminated run of RG-6 then place taps wherever you need to.

Solder Back In/Outdoor Coupler - In Line Style 16dB Loss | Blonder Tongue | 1940-16

 

[IdaScan]

A system that uses taps is usually amplified to make up for the loss in the taps, otherwise you will loose 10dB, 20dB or whatever the tap value is. There is probably no stub effect in the described problem, the jumpers would be way too short at AM broadcast to be resonant and cause any interaction. A quality splitter operated within its range should have at least 20dB isolation between output ports and unterminated or "stubed" ports would cause a small VSWR problem but that's about it.
More than likely its what N-Jay mentioned or it could be LO leakage from radio to the other causing interference.
prcguy

I've exchanged PMs with the OP quite a bit...

Taps work well in a unity gain system, i.e. 0 dB in to amplifier, 15 dB out in to 15 dB tap resulting in 0 dB signal on the 2, 4 or 8 ports of the tap. 0 dB in, 0 dB out.

Directional couplers work in a similar nature, however, their insertion loss is minimal on the "through" port and vary from 6 to 30 dB on the "tap" port.

I use this setup at home to power 4 receivers off of a common amplifier and antenna:
Antenna
50' LDF4 Andrew Heliax
Polyphaser
Bandpass filter
FM notch filter
15 dB CATV amplifier
High pass filter
9 dB Direction Coupler
4 value 4 port tap

This gives roughly a 0 dB gain from the input of the filtering through the amplifier to each tap port.

But in the case, as the OP has found, the 2 way splitter's lack of isolation is likely causing the issue.

 

[N_Jay]

. . I use this setup at home to power 4 receivers off of a common amplifier and antenna:
Antenna
50' LDF4 Andrew Heliax
Polyphaser
Bandpass filter
FM notch filter
15 dB CATV amplifier
High pass filter
9 dB Direction Coupler
4 value 4 port tap

This gives roughly a 0 dB gain from the input of the filtering through the amplifier to each tap port.

I wonder what the true sensitivity and noise figure of the system is and how it would compare to a simple 4 way splitter.

Although with all that filtering I would think a good low noise amplifier would do much better then a CATV amp.

But in the case, as the OP has found, the 2 way splitter's lack of isolation is likely causing the issue.

I still question that, certainly at the AM B-Cast band and a discone antenna.

 

[IdaScan]

I wonder what the true sensitivity and noise figure of the system is and how it would compare to a simple 4 way splitter.

Although with all that filtering I would think a good low noise amplifier would do much better then a CATV amp.



I still question that, certainly at the AM B-Cast band and a discone antenna.

On an HP spectrum analyzer, it brought the noise floor up from the input to filtering to the output of the tap up about 1.5 dB within the pass band.

The same setup, minus the amplifier portion, had a flat noise response, however, resulted in a net loss of 9 dB from input of the filtering to output of the splitter. Insertion loss of splitters is typically 3.5 dB per port on a 2 way, 5.5 dB on a balanced 3 way, 7 dB on a 4 way, and somewhere between 11 and 11.5 dB on 6 and 8 way splitters.

Amplifiers add distortion and noise no matter what. Splitters & Taps add loss. In most cases, the CATV equipment I use has as low or lower noise figures than the typical "Mirage" hammo stuff with a considerably more predictable response curve.

And I agree with N_Jay - reception will be questionable on the AM band either when using the discone.

 

[KK4HG]

What you may be experiencing is the "stub effect"

When using a splitter, any coax or device on either port tends to effect the other.

You need to use taps instead of splitters.

A tap will isolate the the equipment and coax runs from each other and eliminate any interaction.

Using taps, you can run one terminated run of RG-6 then place taps wherever you need to.

Solder Back In/Outdoor Coupler - In Line Style 16dB Loss | Blonder Tongue | 1940-16

As previously noted, a discone is not a AM broadcast antenna and actually if all your connections
are working properly, AM broadcast SHOULD be greatly attenuated since the splitter will not pass signals
below 5mhz without large attenuation and the coax shield will take care of the rest.

I realize the attenuation occurance from the splitter. However, when the PSR600 is disconnected from the splitter and the AR3000A remains connected to the splitter, AM reception is more than acceptable, considering what it is like when both radios are connected to the antenna via the splitter.

I realize the discone is a poor choice for AM reception. I did not buy it for AM. I am simply trying to make do with what I have. I am limited by space and physical ability.

As mentioned in my original post, or hinted to at best, some AM stations come through just fine. 1240 and 1460 for example receive great but 740 sucks when both rigs are connected. Of course 740 is the station I like the most.

AM reception is a side bar, not a necessity with his set up. If I can make it work, then fine. On recommendation from a fellow RR 'r I ordered an Extreme Broadband splitter which has considerably more isolation than the one currently in use. And, it was a fraction of the cost.

If it does not work I may go the tap route although I don't understand how isolation enters into this type of install?!! Of course I could always get a combiner/multicoupler but damn, they're expensive!

 

[IdaScan]

Splitters in these applications are designed for signal to come IN from the input port and OUT from the output ports.

Isolation ratings in this application can be described as kind of like a one way valve between the IN and OUT ports of a splitter. It allows signal from the IN port to flow to the OUT ports, however, does not allow signal (i.e. noise, hum, CPD, etc) to flow from OUT port to OUT port. In a splitter of "good design", a "bad" signal level would need to be at least 110 dB stronger, for example, on OUT port 1 that the signal in the IN port before it would negatively affect the signal being fed to OUT port 2, and vice versa. Keeping in mind that this "bad" signal will still flow back in to the antenna/drop system through the IN port and wreak havoc on whatever is further upstream of it in a CATV operation (not so much of a concern here in OTA reception land).

Unfortunately, a lot of the more common splitters available at consumer stores, such as home improvement warehouses, Radio Shack, office/electronic supply stores like Best Buy and the defunct Circuit City, lack the quality and engineering necessary to provide sufficient signal isolation from port to port. Poor quality components, "gold plating=quality" mantra, glued on back covers and often times shorted out leads within the splitter housing all allow for both signal egress (leakage) and ingress (in the form of noise). A quality splitter will *not* be gold in sheen, have a soldered back panel and typically potted components.

The "Walmart Special" T shaped splitter commonly found at most stores (and most homes illegally connected to CATV service) under the Phillips brand new showed 4.1 dB loss from IN to OUT ports, passed AC power and sat squarely at 35 dB of port to port isolation. A simple "push" on the back panel of the backing plate usually causes it to crush inwards, shorting out on the bare copper wire used to bridge the ports. Last time I checked, glue/expoxy was not good shielding material!

Sorry for the tangent!

 

[N_Jay]

There seems to be a lot of confusion about what is probably going on with this setup.
(I apologize in advance for addressing the issues out of order, as I think it will make the answer clearer.)

I realize the discone is a poor choice for AM reception. I did not buy it for AM. I am simply trying to make do with what I have. I am limited by space and physical ability.

Unless the discone is HUGE, it is not at all acting as an antenna at the AM B-Cast frequencies. What you have is essentially an unterminated piece of transmission line with a few miscellaneous loose ends, none of them of any significant length.
Being as the transmission line is unterminated the shield is just as likely to be a radiating element as any other portion of the network.

I realize the attenuation occurrence from the splitter. However, when the PSR600 is disconnected from the splitter and the AR3000A remains connected to the splitter, AM reception is more than acceptable, considering what it is like when both radios are connected to the antenna via the splitter.

Since your system is working into an (effectively) unterminated line, I would not count on the splitter to act as much more then a conductive block tying the shields of the various lines together. As a test you could terminate each end with dummy load and ground the shield and see if the results are any different than having the radio hardware attached. You can also try it with the radio on and off to see if it is LO leakage or some other effect.

As mentioned in my original post, or hinted to at best, some AM stations come through just fine. 1240 and 1460 for example receive great but 740 sucks when both rigs are connected. Of course 740 is the station I like the most.

With a random antenna system random results should be expected.

AM reception is a side bar, not a necessity with his set up. If I can make it work, then fine. On recommendation from a fellow RR 'r I ordered an Extreme Broadband splitter which has considerably more isolation than the one currently in use. And, it was a fraction of the cost.

I would doubt you will see a significant difference. You may try some thoughtfully constructed experiments to help understand what is happening.
Some ideas are placing an open or a load at each radio port, or even instead of the antenna.
Grounding or ungrounding each load and splitter unit, etc.

If it does not work I may go the tap route although I don't understand how isolation enters into this type of install?!! Of course I could always get a combiner/multicoupler but damn, they're expensive!

I think without understanding what is happening you are grasping at straws.

If you mean be a "combiner/multicoupler", and amplified splitter, you will not find one that covers the AM band and the LMR bands.

 

[N_Jay]

IDASCAN,
Are you saying that you expect a "good" splitter to have a 110dB port to port isolation specification?

In general, the cheap crap sold for cable TV is plenty good for scanner use. (With the exception if the back is pressed in)

As for being glued together, most even at the $1.99 level use a conductive sealant and it works just fine (as long as you don't push the back in.)

Many of the good ones use a sealant that is colored silver and looks like solder, but it is not. That being said, if you find a brand that uses solder, all the better.

 

[IdaScan]

IDASCAN,
Are you saying that you expect a "good" splitter to have a 110dB port to port isolation specification?

In general, the cheap crap sold for cable TV is plenty good for scanner use. (With the exception if the back is pressed in)

As for being glued together, most even at the $1.99 level use a conductive sealant and it works just fine (as long as you don't push the back in.)

Many of the good ones use a sealant that is colored silver and looks like solder, but it is not. That being said, if you find a brand that uses solder, all the better.

EMI shielding and port to port isolation are two separate things in which I appear to have mixed up.

Shielding should be as good as one can find within the bounds of their budget.

Port to port isolation, even on the soldered back plate Holland GSV-2, is around 25-30 dB depending upon frequency. I prefer Regal or another similar brand for passives, but for the several thousand we go through a month, it's sufficent.

What's sad is the "cheap crap sold for cable TV" should really not be marketed for anything more than antenna OTA reception

Sorry for the confusion I may have caused - N_Jay is on track on this issue.

 

[lmrtek]

Hams and scanner listeners seem to try and re-invent the wheel when it's not necessary.

If Cable TV companies used splitters, they would not only run out of signal a few blocks from the head end,
but those who DID get a picture would likely have all sorts of reception problems.

Splitters may work for many installations, but taps are simply the ONLY way to distribute signals
without creating a stub that notches out a desired signal or creating interaction (birdies) between the two scanners.

Scanners are very good signal generators.

They generate as many signals as they receive.

This means these generated signals will be transmitted from one scanner to the other using a splitter.

My earlier copy and paste was in error.

I meant to copy and paste the 4 db tap instead.

Directional taps are best but can be costly.

 

[prcguy]

When speaking of good vs cheap TV splitters, the only real difference I have found with most brands is they are all in the 99c category and if you spend $14 on one, someone made $13 profit.

Here is something else to consider regarding the original question. The VHF/UHF Discone is going to be an extremely high impedance at 1MHz, probably 2K oms or more. When you see short, active VLF/HF whips around 1m long, the active part of the antenna is using a FET as an impedance matching and current driving device rather than a preamp.

The Discone will have tremendous loss feeding 50 or 75ohm coax because of the very high source impedance feeding the low impedance feedline. Add to this the TV splitter probably has no port to port isolation at 1MHz and acts more like a T connector. In this case adding a second receiver (load) on the splitter will probably reduce the overall impedance seen at the antenna because the 15ft of coax is an insignificant portion of a wavelength at 1MHz.

The end result should be a reduction in level at one receiver when the other is connected, unlike the same system operated at higher frequencies and within the rated range of the components.
prcguy

 

[N_Jay]

Hams and scanner listeners seem to try and re-invent the wheel when it's not necessary.

If Cable TV companies used splitters, they would not only run out of signal a few blocks from the head end,
but those who DID get a picture would likely have all sorts of reception problems.

Splitters may work for many installations, but taps are simply the ONLY way to distribute signals
without creating a stub that notches out a desired signal or creating interaction (birdies) between the two scanners.

Scanners are very good signal generators.

They generate as many signals as they receive.

This means these generated signals will be transmitted from one scanner to the other using a splitter.

My earlier copy and paste was in error.

I meant to copy and paste the 4 db tap instead.

Directional taps are best but can be costly.

The assumption that the engineering if an HFC system and the engineering of a receiver multi-coupler system is the same is in error.

A tap (not a directional coupler) with very low lost will have isolation figures the same or very similar to a splitter of the same loss.

 

[prcguy]

Taps are not the only way. Part of my job is designing large commercial TV and L-band distribution systems and each device has its purpose and place. Taps have no place in the average scanner distribution in my opinion and neither do noisy IMD prone CATV amplifiers."Stub" problems are not a concern when using splitters within their frequency range except for some minor VSWR and amplitude ripple.

If cable companies didn't amplify the signal dozens of times (many dozens?) and charge an arm and a leg for a crappy fuzzy picture, then we wouldn't have to go the satellite route now would we....
prcguy

Hams and scanner listeners seem to try and re-invent the wheel when it's not necessary.

If Cable TV companies used splitters, they would not only run out of signal a few blocks from the head end,
but those who DID get a picture would likely have all sorts of reception problems.

Splitters may work for many installations, but taps are simply the ONLY way to distribute signals
without creating a stub that notches out a desired signal or creating interaction (birdies) between the two scanners.

Scanners are very good signal generators.

They generate as many signals as they receive.

This means these generated signals will be transmitted from one scanner to the other using a splitter.

My earlier copy and paste was in error.

I meant to copy and paste the 4 db tap instead.

Directional taps are best but can be costly.

 

[KK4HG]

Wow! What a great collection of information! I want to thank all of you for the input as well as the spirited debate!:roll:

An update: On IdaScan's recommendation, I purchased an "Extreme Broadband", 1gHz splitter with 120dB isolation between ports. It works great! My signal level to the AR3000A is up about 6-9dB based on the increase in audio (no mesurement was taken). The damn thing was less than $3.00 shipped compared o the lowes special which was about $16.00. Further investigation revealed that this "special" had no marking for isolation figures.

Again, I realize my installation is far from pure. I just want to make things work at an acceptablre level, not optimum. When the weather stabilizes I will probably get the discone outside and put up a long wire somewhere for the AR3000A. That way I can put the PSR600 on the discone by itself.

Thanks again, fellas...it's been real!

 

[lmrtek]

Taps are not the only way. Part of my job is designing large commercial TV and L-band distribution systems and each device has its purpose and place. Taps have no place in the average scanner distribution in my opinion and neither do noisy IMD prone CATV amplifiers."Stub" problems are not a concern when using splitters within their frequency range except for some minor VSWR and amplitude ripple.

If cable companies didn't amplify the signal dozens of times (many dozens?) and charge an arm and a leg for a crappy fuzzy picture, then we wouldn't have to go the satellite route now would we....
prcguy

I actually laid out designed and installed MATV systems for 20 years.

I did 2,000 room hotels in Vegas and entire head ends and distribution in cities with 300,000 taps.

Without exception any time a customer had an interaction or "stub" problem,
it was due to the use of splitters for the reasons I already sited..

And my $16,000 dollar service monitor never lies to me so I tend to believe what it shows

That's not my opinion, it's what the Anritsu showed.




; )

 

[prcguy]

I'm not saying my HP 50ohm network analyzer or Agilent dedicated 75ohm network analyzer trumps your Anritsu or that you don't have experience but I will say that a stub will not cause more than maybe 2 dB or so ripple in the amplitude response at the output of common splitters used for scanner use. My definition of a stub would be an unterminated or improperly terminated length of coax at a splitter output.

Most of the large distribution systems I deal with are 950 to 2150MHz where connector terminations might pass for CATV or MATV use but will show problems at 2Ghz. Even at 2GHz I cannot mess up a 2-way or 4-way splitter output with stubs or open ports that will cause more than a few dB of ripple or a frequency suck out on the other properly terminated ports because of the 20dB or more isolation between ports on a reasonable quality splitter.

If you use a splitter outside its frequency range where the isolation degrades to nothing or there is no isolation to start with I could definitely see a problem.
prcguy

I actually laid out designed and installed MATV systems for 20 years.

I did 2,000 room hotels in Vegas and entire head ends and distribution in cities with 300,000 taps.

Without exception any time a customer had an interaction or "stub" problem,
it was due to the use of splitters for the reasons I already sited..

And my $16,000 dollar service monitor never lies to me so I tend to believe what it shows

That's not my opinion, it's what the Anritsu showed.




; )