Cannot Find a Diplexer for ~100-500 and ~700-1000 MHz

MDScanFan

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I researched diplexer options and cannot find what I am looking for. I would like to combine a discone for coverage from ~100 MHz up to 450-500 MHz with another higher frequency discone for ~700 up to 1000-1200MHz. This would be fed to a broadband receiver.

I found some references on this forum to suitable diplexers that pop up from time to time on eBay, such as one from K&L. Is anyone aware of an available diplexer that meets my general frequency requirements?
 

mmckenna

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mmckenna

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prcguy

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This is the very best diplexer I have found covering 80 through 520Mhz on one port and 694 to 2700MHz on the other, perfect for scanner use. The low frequency port goes down to nearly DC. That means you could double diplex in the VHF lo band and or the HF band with the 80-520MHz stuff.

Problem is this diplexer is expensive new but over the last year I got one NIB for $100 and another for $150. They are out there if you are patient.

 

MDScanFan

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I should have mentioned a price target. I would like to spend under around $100 for the diplexer. Also, I would like it to cover down to at least 108 MHz so it will cover the airband. Lower coverage is icing on the cake, it not critical. The Tessco models look nice but much too expensive for me. I also came across a model by Amphenol DIPX 500/800-2.5G. It states call for a quote, which surely means it is above my price target. I will keep my eye on the used market for something suitable. It isn’t unfortunate there is no suitable Comet or Diamond models.
 

iMONITOR

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I researched diplexer options and cannot find what I am looking for. I would like to combine a discone for coverage from ~100 MHz up to 450-500 MHz with another higher frequency discone for ~700 up to 1000-1200MHz. This would be fed to a broadband receiver.

I found some references on this forum to suitable diplexers that pop up from time to time on eBay, such as one from K&L. Is anyone aware of an available diplexer that meets my general frequency requirements?
An alternative approach to consider:

AOR SA7000 Wide Band Antenna

Spec Sheet .pdf file attached
 

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KevinC

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I should have mentioned a price target. I would like to spend under around $100 for the diplexer. Also, I would like it to cover down to at least 108 MHz so it will cover the airband. Lower coverage is icing on the cake, it not critical. The Tessco models look nice but much too expensive for me. I also came across a model by Amphenol DIPX 500/800-2.5G. It states call for a quote, which surely means it is above my price target. I will keep my eye on the used market for something suitable. It isn’t unfortunate there is no suitable Comet or Diamond models.
If you can deal with a little high VSWR in the 700 band (around 3:1 769 and 2:1 at 799) this one from Comet should work for you.

 

MDScanFan

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That looks like it should work for my situation and the price is right. I only need it from around 769 upward and a 3:1 vswr should be fine. Did you get those values from a datasheet or did you have a measurement? I could not locate a data sheet for the 413b.

If you can deal with a little high VSWR in the 700 band (around 3:1 769 and 2:1 at 799) this one from Comet should work for you.

 

KevinC

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That looks like it should work for my situation and the price is right. I only need it from around 769 upward and a 3:1 vswr should be fine. Did you get those values from a datasheet or did you have a measurement? I could not locate a data sheet for the 413b.
From my measurements. I've tested 2 and they both swept the same, but I make no guarantees all of them will sweep the same outside their intended range.

And they went to slightly over 500 MHz (at 2:1) on the other port in case you were wondering.
 

Ubbe

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Maybe you can make a diplexer yourself if you can solder and put in a metal can of your choise, with coaxes soldered directly to the circuit or with connectors on the box. It's 5 components for a lowpass filter and 5 for a highpass filter that you connect in parallell to the scanner and the other end of each filter toits antenna, and components are 25 cent each. You can gut out a $5 CATV splitter and use as you then have box and connectors already in place and can probably solder and hotglue on the existing circuitboard if you remove its components.


Select a 5 pole Butterworth filter and series first. Then use 525Mhz as the lowpass and 675MHz as the highpass frequency.

/Ubbe
 

prcguy

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The back comes off those and you can get at the parts inside. You can glue a little piece of #43 mix ferrite to one side of a stick (or a threaded slug out of an adjustable coil will sometimes work for the ferrite) and some brass (a #6 brass nut will work) on the other end of the stick and place the ferrite or brass against the coils one by one to see if it pulls the tuning in a favorable direction while sweeping the band pass. If the ferrite makes it better then squeezing the coil should work and if the brass makes it better spreading the coil should make it better. Or maybe its the other way around....

Anyway they might tune a little better for scanner use with some playing around.

1.5 dB at 500 MHz and 2.5 at 769 MHz.
 

KevinC

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The back comes off those and you can get at the parts inside. You can glue a little piece of #43 mix ferrite to one side of a stick (or a threaded slug out of an adjustable coil will sometimes work for the ferrite) and some brass (a #6 brass nut will work) on the other end of the stick and place the ferrite or brass against the coils one by one to see if it pulls the tuning in a favorable direction while sweeping the band pass. If the ferrite makes it better then squeezing the coil should work and if the brass makes it better spreading the coil should make it better. Or maybe its the other way around....

Anyway they might tune a little better for scanner use with some playing around.
Or you could just not worry about an extra 1 dB at 500 and 2 dB at 769. My ear is only calibrated to notice a difference greater than 3 dB. :p
 

APX8000

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I had a company called U.S. Communications (bear-electronics.com) make me a custom diplexer.....0-520 on a Diamond D130NJ Discone and 700-1300 on a Terrawave 700 Omni. They make a lot of covert antenna solutions for all the alphabet agencies. The owner is very responsive, reasonably priced for what you’re getting and can center it in each band for your needs (pic attached).

The Microlab BK-24N is another choice, but hundreds more than the custom one I just had made. As prcguy stated, they can be had on auction sites but you have to be patient and act quick.
 

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prcguy

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I wish you would have mentioned what you were ordering before you ordered. Here is the inside of a US Communications antenna adapter and they make similar units for multiband antenna diplexing. This unit doesn't even follow the basic criteria for a Wilkinson divider. You might open yours to see what's in it. If its just lengths of coax I would send it back. Or sweep it to see how bad it is first, then send it back, unless it has coils and caps for low, band and high pass.

IMG_4088.JPG

IMG_4089.JPG
I had a company called U.S. Communications (bear-electronics.com) make me a custom diplexer.....0-520 on a Diamond D130NJ Discone and 700-1300 on a Terrawave 700 Omni. They make a lot of covert antenna solutions for all the alphabet agencies. The owner is very responsive, reasonably priced for what you’re getting and can center it in each band for your needs (pic attached).

The Microlab BK-24N is another choice, but hundreds more than the custom one I just had made. As prcguy stated, they can be had on auction sites but you have to be patient and act quick.
 
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