Custom triplexer/quadplexer made from notch filters and combiner?

jsncrso

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Trying to find a solution for my setup to combine several antennas into one line to feed multiple receivers (trying not to have a bunch of LMR400 lines). I have three white stick antennas (162, 850, & 978/1090MHz) plus a discone (general ~450MHZ) that I want to feed into a single LMR400 cable down to a multi coupler. Of course, there are no commercial tri/quadplexers that will achieve this and I have several receivers that will need to pull in multiple frequencies, so individual coax lines aren't the best solution.

Anyway, my question is would adding individual notch filters to the inputs of a splitter/combiner achieve the same isolation and low insertion loss that an off the shelf triplexer would achieve? Trying not to get overly complicated here, but with my limited knowledge on RF behavior, I'm just not sure. Thoughts??
 

WRMD298

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How critical will your receive signal be? Are you routinely listening to signals that are borderline readable or is everything pretty much full-quieting to begin with? You may be able to get by with just one single antenna that covers all of the above. The Diamond D130NJ is a perfect example, covering up to 1300 MHz and offering 2 dBi gain (about the gain as a 1/4 wave on each band). Depending on what kind of "white stick" antennas you have, you may not be losing much gain.. a 10-foot white stick at 160 MHz has around 5.1 dBi gain, however, a 10-foot stick at 800 MHz may have as much as 10 dBi gain. You might be able to afford an 8 dB loss to achieve convenience. Let's say you did have a multi-band coupler that did all of the above frequencies. You would need to weatherproof it at the tower top first of all, and 2nd, with that frequency spacing, you would have some measurable loss through each port even in the most ideal conditions. Running a multi-band discone through a low-noise multicoupler to each receiver sounds like the way to go. Depending on the noise figure on your receivers versus the noise figure of the multicoupler amplifier, you may come out better perfoemance-wise than running four separate antennas and lines.

I have a Diamond D130NJ at my shop and it's a great convenient antenna that may do exactly what you want.
 

prcguy

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There are off the shelf diplexers/triplexers that will do what you want. You would need a diplexer that separates the 700-900 bands and 978-1090 band then stick the combined bands into the 700/800 port of a triplexer, then the 150 and 450 antennas into the VHF and UHF ports of the triplexer. Most triplexers 700-900 range is just a high pass and it will accept frequencies above that. You could also find a 900MHz low pass filter and a 900 high pass then combine the two higher freq antennas into the triplexer 800 port. It would be better if each 800/1090 antenna had a separate LNA then you could combine with a simple splitter and not worry about the 3dB splitting loss.

I just picked up another triplexer, a Panorama that has a 136-174 port, 380-520 port and a 760-896 port for $66 on eBay and I’ll be testing its 800 port to see if it will pass above 896MHz. eBay is your friend for diplexers, triplexes and filters.

 

prcguy

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How critical will your receive signal be? Are you routinely listening to signals that are borderline readable or is everything pretty much full-quieting to begin with? You may be able to get by with just one single antenna that covers all of the above. The Diamond D130NJ is a perfect example, covering up to 1300 MHz and offering 2 dBi gain (about the gain as a 1/4 wave on each band). Depending on what kind of "white stick" antennas you have, you may not be losing much gain.. a 10-foot white stick at 160 MHz has around 5.1 dBi gain, however, a 10-foot stick at 800 MHz may have as much as 10 dBi gain. You might be able to afford an 8 dB loss to achieve convenience. Let's say you did have a multi-band coupler that did all of the above frequencies. You would need to weatherproof it at the tower top first of all, and 2nd, with that frequency spacing, you would have some measurable loss through each port even in the most ideal conditions. Running a multi-band discone through a low-noise multicoupler to each receiver sounds like the way to go. Depending on the noise figure on your receivers versus the noise figure of the multicoupler amplifier, you may come out better perfoemance-wise than running four separate antennas and lines.

I have a Diamond D130NJ at my shop and it's a great convenient antenna that may do exactly what you want.
I like Discones but there is an inherent problem where about halfway through its 8:1 frequency range the radiation pattern shifts upward above horizon resulting in up to 10dB loss In the 800-900MHz range. I’ve measured the Diamond D130, Radio Shack and one by MP antenna, all the same basic size Discone and they are about 10dB down at 800MHz compared to a small Discone designed for the roughly 300-2400MHz range where the pattern is still at the horizon at 800MHz.

The fix is to let the typical scanner Discone like the D130 do it’s job in the 118 to 512MHz range where it’s performance at the horizon is consistent, then supplement with a modest gain 700-800-900MHz antenna and diplex them. I’ve been using and recommending an Lcom HGV-906U that has about 6dBi gain over the upper 700MHz through 960MHz range. These antennas can be had off eBay sometimes for $20-$30.

I have many high gain single band antennas combined and it’s hard to beat if you have the budget and space. I’ve got 21ft wide band VHF omni‘s, wide band VHF dipole arrays with 9dBd gain, wide band UHF dipole arrays with 9dBd gain, 15ft wide band 800/900 sticks with 8.5dBd gain and adjustable downtilt and various diplexers, triplexes, quadplexers and pentaplexers to make them and other antennas play into one common feed. Then end result is so much better than a single Discone and it will hear things at distances a Discone could never do.

I‘ve been able to put this all together very cheap over the years with careful shopping, kind friends and a forgiving wife. I still have a garage full of Discones and several on the roof but when it’s time to get serious with weak signals or extreme distances, nothing beats an arsenal of high gain antennas. I think the OP will see a big improvement over the Discone if he can find the parts to combine the antennas he mentioned.
 
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WRMD298

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Jan 29, 2024
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I like Discones but there is an inherent problem where about halfway through its 8:1 frequency range the radiation pattern shifts upward above horizon resulting in up to 10dB loss In the 800-900MHz range. I’ve measured the Diamond D130, Radio Shack and one by MP antenna, all the same basic size Discone and they are about 10dB down at 800MHz compared to a small Discone designed for the roughly 300-2400MHz range where the pattern is still at the horizon at 800MHz.

The fix is to let the typical scanner Discone like the D130 do it’s job in the 118 to 512MHz range where it’s performance at the horizon is consistent, then supplement with a modest gain 700-800-900MHz antenna and diplex them. I’ve been using and recommending an Lcom HGV-906U that has about 6dBi gain over the upper 700MHz through 960MHz range. These antennas can be had off eBay sometimes for $20-$30.

I have many high gain single band antennas combined and it’s hard to beat if you have the budget and space. I’ve got 21ft wide band VHF omni‘s, wide band VHF dipole arrays with 9dBd gain, wide band UHF dipole arrays with 9dBd gain, 15ft wide band 800/900 sticks with 8.5dBd gain and adjustable downtilt and various diplexers, triplexes, quadplexers and pentaplexers to make them and other antennas play into one common feed. Then end result is so much better than a single Discone and it will hear things at distances a Discone could never do.

I‘ve been able to put this all together very cheap over the years with careful shopping, kind friends and a forgiving wife. I still have a garage full of Discones and several on the roof but when it’s time to get serious with weak signals or extreme distances, nothing beats an arsenal of high gain antennas. I think the OP will see a big improvement over the Discone if he can find the parts to combine the antennas he mentioned.
100% agreed with everything you said except for the very last sentence. The OP may see ZERO improvement in a listening-fashion over four individual high-gain antennas verses a coat hanger hanging from a tree depending on exactly what he is listening for. If all services he is listening to are already, for example, a -90 dBm with a discone then converting to higher gain antennas won't help is performance if performance is rated as hearing a full-quieting signal coming out of his speaker(s). If one was measuring RSSI in a sort of receive-competition where the strongest signal wins, then clearly, going with higher gain, separate antennas and doing the pattern calculations on the discone as you mentioned would definitely win the prize. Clearly, if the OP is routinely trying to listen to very distant, marginal signals, then separate antennas would clearly be best, but he didn't specify the range he was looking for. OP, please clarify for us the signals you are looking to receive and about how far away they are from your antenna, and are all the signals fairly strong?

I once helped a fellow ham who is pretty intelligent save a few $K on repeater equipment. He was going to purchase a "bigger" antenna, a power amplifier, and better feed-line. The total increase in talk-out performance would be around 7 dB, and the talk-in performance due to the better antenna and line would be around 5 dB. I asked him what he was trying to accomplish, and he said he wanted the repeater to "work better." I asked him when, if ever, any of the repeater users were routinely on the fringe area, having difficulties getting in or receiving the machine to the point it was irritating, and what exactly he wanted the repeater to do "better" that it wasn't already doing. After thinking on this for a while, he realized that the machine was already, and had for years been doing exactly what he wanted and needed it to do, therefore, making it "better" was just a psychological ideal that he thought he wanted, but realized it would actually accomplish nothing. He spent the money on a nice HF station instead.
 

prcguy

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100% agreed with everything you said except for the very last sentence. The OP may see ZERO improvement in a listening-fashion over four individual high-gain antennas verses a coat hanger hanging from a tree depending on exactly what he is listening for. If all services he is listening to are already, for example, a -90 dBm with a discone then converting to higher gain antennas won't help is performance if performance is rated as hearing a full-quieting signal coming out of his speaker(s). If one was measuring RSSI in a sort of receive-competition where the strongest signal wins, then clearly, going with higher gain, separate antennas and doing the pattern calculations on the discone as you mentioned would definitely win the prize. Clearly, if the OP is routinely trying to listen to very distant, marginal signals, then separate antennas would clearly be best, but he didn't specify the range he was looking for. OP, please clarify for us the signals you are looking to receive and about how far away they are from your antenna, and are all the signals fairly strong?

I once helped a fellow ham who is pretty intelligent save a few $K on repeater equipment. He was going to purchase a "bigger" antenna, a power amplifier, and better feed-line. The total increase in talk-out performance would be around 7 dB, and the talk-in performance due to the better antenna and line would be around 5 dB. I asked him what he was trying to accomplish, and he said he wanted the repeater to "work better." I asked him when, if ever, any of the repeater users were routinely on the fringe area, having difficulties getting in or receiving the machine to the point it was irritating, and what exactly he wanted the repeater to do "better" that it wasn't already doing. After thinking on this for a while, he realized that the machine was already, and had for years been doing exactly what he wanted and needed it to do, therefore, making it "better" was just a psychological ideal that he thought he wanted, but realized it would actually accomplish nothing. He spent the money on a nice HF station instead.
If the OP lives in a bubble where all things he listens to are full quieting and never change, then sure a lousy antenna should be just fine. But when has anyone in this hobby ever been happy with everything they try to hear?

So Derek, are you happy with everything you listen to? Ever wonder what else might be out there in the distance that you can’t pick up right now?
 

WRMD298

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If the OP lives in a bubble where all things he listens to are full quieting and never change, then sure a lousy antenna should be just fine. But when has anyone in this hobby ever been happy with everything they try to hear?

So Derek, are you happy with everything you listen to? Ever wonder what else might be out there in the distance that you can’t pick up right now?
Yes. I must live in a bubble also.
 
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