prcguy
Member
I've been wanting to provide my Icom R8600 with a really good wide band VHF/UHF antenna system and I finally have a plan coming together. The only way to get the bandwidth with no gaps is with Discones and one Discone can't possibly cover the 100Mhz to 3GHz capability of the radio, so I'm using two. I found Discones rated for 100 to 800MHz loose about 10dB of gain at the horizon in the 800Mhz range so I found a nice small version that covers about 400Mhz to 3GHz and receives about 10dB better at 800/900Mhz than the big one.
I also have two listening areas, one about 75 ft down the coax from the antennas and the other has about 150ft of coax, which is Andrew 1/2" Superflex Heliax in this case. Even with Heliax there will be a lot of loss at higher frequencies so I will use some (dreaded) preamps to make up for feedline and splitter loss. Using a bunch of stuff laying around and buying a few needed parts, I assembled what I hope will be a bullet proof tower top filtered and diplexed preamp.
I was originally going to use a MiniCircuits ZX60-P103LN for both Discones, but that preamp falls way off in gain above 1GHz and even from about 100MHz to 1GHz it looses about 10dB of gain. Since its about the lowest noise figure VHF/UHF amp they offer (.4dB) with reasonable IP1/IP3 I'll use it for 100-512Mhz range and a ZRL-3500 series for 700MHz on up with a higher noise figure around 2.5dB.
The higher frequency side will start with a Maxrad brand Discone that covers about 400MHz through maybe 3GHz and feeds the high freq input connector to a high pass filter that will pass signals from 3GHz down to about 700Mhz then rolls off about 40dB at 512Mhz. That feeds the ZRL-3500 preamp then the high side 694 to 2.7GHz input of a diplexer.
The low freq side will use an Astron Wireless Discone that covers about 100Mhz to over 500Mhz to the low freq input of the box, then a 550Mhz low pass filter, then a commercial 88-108Mhz notch filter then to the ZX60-P103LN preamp. That would normally feed the 80 to 520Mhz input of the diplexer, but I made a last minute change to add a 30-90MHz non amplified input for VHF lo band. The common port of the military diplexer will feed the 80-520MHz input of the main diplexer. I also put a 25Mhz high pass filter on the 30-90Mhz input as the COM201B will be within about 20ft of my main 40/80m antenna that can run near full legal limit.
The main diplexer would be excellent for most people combining a high and low frequency Discone or a Discone and seperate 700/800/900MHz antenna using a low loss feedline. Its a Microlab BK-24N with an 80-520MHz input and a 694-2700Mhz input, a perfect split for covering commercial, public service and amateur freqs. To add VHF lo band the output of the VHF/UHF ZX60-P103LN preamp feeds a military surplus diplexer that has a 30-90Mhz input and a 116 to 520Mhz input, perfect for my application. I'll be using a military broad band Cobham COM201B ground plane to cover the 30-90MHz range into a third input on the tower mounted box.
Power for the preamps will be fed up the coax to a MiniCircuits bias tee that is now operating a little beyond its current rating and I'll have to inject at least 15 volts into the coax to get 12 volts to one of the preamps designed for 12 volts. The other preamp runs on 5 volts provided by a 3 terminal linear regulator in the box. Coax runs from the Discones will be about 6ft each and maybe 40ft of LMR400 from the COM201B to the tower mounted box. I hope to have it installed within a few days and hopefully the preamps are filtered well enough to survive the high RF levels in this area. I will be swapping out the 88-108Mhz notch filter with a high pass filter with a cutoff around 110MHz once I locate one.
BTW, I was feeling a bit lazy so the construction of the box is not my best and I purchased most of the interconnect cables inside the box. I would normally use flexible .141 semi rigid but I don't have enough connectors in stock and commercially made cables are about $25 on up each. I instead used RG-316 jumpers, a few I had made and the rest I got on Ebay from americancoax1, a local So Cal mfr. I'm really happy with the quality and workmanship and most cables were in the $7 range with free shipping, and the cables were delivered the next day. Can't beat that.
Looking at the picture below the 700-3000MHz input is on the top left, the 100-520Mhz input on the top right, the 30-90Mhz input is on the bottom right and the main output/DC input is on the bottom left. Since the main diplexer will go down to almost DC on its 80-520MHz input I could put in a future input for VLF/HF using a third diplexer.
I also have two listening areas, one about 75 ft down the coax from the antennas and the other has about 150ft of coax, which is Andrew 1/2" Superflex Heliax in this case. Even with Heliax there will be a lot of loss at higher frequencies so I will use some (dreaded) preamps to make up for feedline and splitter loss. Using a bunch of stuff laying around and buying a few needed parts, I assembled what I hope will be a bullet proof tower top filtered and diplexed preamp.
I was originally going to use a MiniCircuits ZX60-P103LN for both Discones, but that preamp falls way off in gain above 1GHz and even from about 100MHz to 1GHz it looses about 10dB of gain. Since its about the lowest noise figure VHF/UHF amp they offer (.4dB) with reasonable IP1/IP3 I'll use it for 100-512Mhz range and a ZRL-3500 series for 700MHz on up with a higher noise figure around 2.5dB.
The higher frequency side will start with a Maxrad brand Discone that covers about 400MHz through maybe 3GHz and feeds the high freq input connector to a high pass filter that will pass signals from 3GHz down to about 700Mhz then rolls off about 40dB at 512Mhz. That feeds the ZRL-3500 preamp then the high side 694 to 2.7GHz input of a diplexer.
The low freq side will use an Astron Wireless Discone that covers about 100Mhz to over 500Mhz to the low freq input of the box, then a 550Mhz low pass filter, then a commercial 88-108Mhz notch filter then to the ZX60-P103LN preamp. That would normally feed the 80 to 520Mhz input of the diplexer, but I made a last minute change to add a 30-90MHz non amplified input for VHF lo band. The common port of the military diplexer will feed the 80-520MHz input of the main diplexer. I also put a 25Mhz high pass filter on the 30-90Mhz input as the COM201B will be within about 20ft of my main 40/80m antenna that can run near full legal limit.
The main diplexer would be excellent for most people combining a high and low frequency Discone or a Discone and seperate 700/800/900MHz antenna using a low loss feedline. Its a Microlab BK-24N with an 80-520MHz input and a 694-2700Mhz input, a perfect split for covering commercial, public service and amateur freqs. To add VHF lo band the output of the VHF/UHF ZX60-P103LN preamp feeds a military surplus diplexer that has a 30-90Mhz input and a 116 to 520Mhz input, perfect for my application. I'll be using a military broad band Cobham COM201B ground plane to cover the 30-90MHz range into a third input on the tower mounted box.
Power for the preamps will be fed up the coax to a MiniCircuits bias tee that is now operating a little beyond its current rating and I'll have to inject at least 15 volts into the coax to get 12 volts to one of the preamps designed for 12 volts. The other preamp runs on 5 volts provided by a 3 terminal linear regulator in the box. Coax runs from the Discones will be about 6ft each and maybe 40ft of LMR400 from the COM201B to the tower mounted box. I hope to have it installed within a few days and hopefully the preamps are filtered well enough to survive the high RF levels in this area. I will be swapping out the 88-108Mhz notch filter with a high pass filter with a cutoff around 110MHz once I locate one.
BTW, I was feeling a bit lazy so the construction of the box is not my best and I purchased most of the interconnect cables inside the box. I would normally use flexible .141 semi rigid but I don't have enough connectors in stock and commercially made cables are about $25 on up each. I instead used RG-316 jumpers, a few I had made and the rest I got on Ebay from americancoax1, a local So Cal mfr. I'm really happy with the quality and workmanship and most cables were in the $7 range with free shipping, and the cables were delivered the next day. Can't beat that.
Looking at the picture below the 700-3000MHz input is on the top left, the 100-520Mhz input on the top right, the 30-90Mhz input is on the bottom right and the main output/DC input is on the bottom left. Since the main diplexer will go down to almost DC on its 80-520MHz input I could put in a future input for VLF/HF using a third diplexer.
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