I've often recommended adding an 800MHz antenna and diplexer to a scanner type Discone to improve 800 reception and did that on an elaborate filtered preamped system a few years back and its working well. Yesterday I gathered up some parts and did the same to a Discone feeding a Harris XG-100M that I've been using as a scanner. I don't do much 800 stuff but I had the parts laying around, so why not?
The Discone in question is an odd MP Antenna model 08-ANT-0861 that has varying length disc radials that bend upward. The mfr suggests that improves multipath problems but more about that later. I did an 800MHz reception test with the MP Discone a year ago logging some signal strengths on the very accurate dBm display of an Icom R8600 then swapped the MP Discone with a much smaller one rated for 300-2,400MHz. I did this because most scanner type Discones start to tilt their radiation pattern upwards around 500Mhz and I wanted to see how much that affects 800 reception. Turns out I picked up about 10dB more signal with the smaller Discone in the 800MHz range and that Discone was mounted on the same mast using the same feedline.
For my upgrade I had several 6dBi rated antennas covering the 800-900MHz range and made an arm to hold one out from the Discone mast using some mast material and aluminum fittings from Nurail. The arm places the 800/900 antenna about 2 wavelengths out from the mast reducing the beam effect some and my goal was to place the top of this antenna a little below the Discone skirt, but a mistake made in cable length forced me to have the top of the 800/900 antenna sticking several inches into the Discone skirt. Probably not a big issue since the diplexer will isolate the antennas some in the 800MHz range and at lower frequencies the Discone should ignore the 800/900 antenna.
I already had this particular diplexer mounted in a steel NEMA box for mast mount and all cables including feedline to the radio are LMR400. Using the RSSI metering in the Harris radio which happens to read out in dBm and is very accurate, I've measured between 10 and 15dB improvement in 800MHz reception with this new addition. Some signals I was receiving are not line of site and fade a bit and they still fade slightly on the new antenna but are much stronger now. Overall it really perked up 800MHz reception and for those using a typical scanner Discone line a Radio Shack, Diamond D130, etc, this is a very worthwhile upgrade.
The 800/900 antenna I used is an L-Com HGV-906U and sometimes available on Ebay for $30-$40. If you get one make sure it comes with the mounting bracket. The diplexer was also an eBay item and similar diplexers come and go all the time for ok prices. Here is a picture of the completed setup and the inside of the NEMA box with diplexer and cables.
On the mfrs claims of their "spatial diversity" and "multi polarized" multipath reducing features, there might be something to this. I did some testing going between the MP Discone and a few other vertical antennas here in my hilly neighborhood and there does seem to be a little less deep fading and picket fencing on the MP Discone compared to the other antennas. There is also less gain on the MP which shows up at extreme distances where signals can be in the noise but other antennas still have some useable signal.
The Discone in question is an odd MP Antenna model 08-ANT-0861 that has varying length disc radials that bend upward. The mfr suggests that improves multipath problems but more about that later. I did an 800MHz reception test with the MP Discone a year ago logging some signal strengths on the very accurate dBm display of an Icom R8600 then swapped the MP Discone with a much smaller one rated for 300-2,400MHz. I did this because most scanner type Discones start to tilt their radiation pattern upwards around 500Mhz and I wanted to see how much that affects 800 reception. Turns out I picked up about 10dB more signal with the smaller Discone in the 800MHz range and that Discone was mounted on the same mast using the same feedline.
For my upgrade I had several 6dBi rated antennas covering the 800-900MHz range and made an arm to hold one out from the Discone mast using some mast material and aluminum fittings from Nurail. The arm places the 800/900 antenna about 2 wavelengths out from the mast reducing the beam effect some and my goal was to place the top of this antenna a little below the Discone skirt, but a mistake made in cable length forced me to have the top of the 800/900 antenna sticking several inches into the Discone skirt. Probably not a big issue since the diplexer will isolate the antennas some in the 800MHz range and at lower frequencies the Discone should ignore the 800/900 antenna.
I already had this particular diplexer mounted in a steel NEMA box for mast mount and all cables including feedline to the radio are LMR400. Using the RSSI metering in the Harris radio which happens to read out in dBm and is very accurate, I've measured between 10 and 15dB improvement in 800MHz reception with this new addition. Some signals I was receiving are not line of site and fade a bit and they still fade slightly on the new antenna but are much stronger now. Overall it really perked up 800MHz reception and for those using a typical scanner Discone line a Radio Shack, Diamond D130, etc, this is a very worthwhile upgrade.
The 800/900 antenna I used is an L-Com HGV-906U and sometimes available on Ebay for $30-$40. If you get one make sure it comes with the mounting bracket. The diplexer was also an eBay item and similar diplexers come and go all the time for ok prices. Here is a picture of the completed setup and the inside of the NEMA box with diplexer and cables.
On the mfrs claims of their "spatial diversity" and "multi polarized" multipath reducing features, there might be something to this. I did some testing going between the MP Discone and a few other vertical antennas here in my hilly neighborhood and there does seem to be a little less deep fading and picket fencing on the MP Discone compared to the other antennas. There is also less gain on the MP which shows up at extreme distances where signals can be in the noise but other antennas still have some useable signal.
