VHF/UHF/800 scanner/transmit antenna project

[prcguy]

Over the years I've collected lots of antennas for projects including some nice Shakespeare marine versions used on Govt vessels. I've had the parts laying around for years to make a VHF/UHF/700/800 setup using discreet marine antennas for each band and a commercial triplexer but never got around to putting it all together. Then a friend got some multiband radios and needed something similar so I gave him a shopping list of what I had not expecting him to actually find all the parts. Well he did and I just finished putting together all his parts into a really nice multiband base antenna that would be great for any scanner enthusiast or someone with a multiband radio like Motorola APX8500, Harris XG-100M, etc.

The individual antennas used are the Shakespeare HS-2774-R covering 136-174MHz with 4dBi gain, a Shakespeare US-3849 covering 380-490MHz with 4dBi gain and a Shakespeare 4800 series designed for 800MHz but covers down into the 700 range just fine. All are rated for shipboard use and should never have a problem from weather or corrosion. All antennas are mounted on a 6ft cross arm giving 1/2 wavelength spacing between antennas at VHF and much more at UHF and 800. Right below the cross arm is an outdoor NEMA rated box containing a high power Motorola triplexer and interface cables providing a single feedline to the radio. All antennas and hardware have been primed and painted grey to soften the impact to neighbors. Mast and cross arm hardware are aluminum castings from NuRail.

This setup should provide a very noticeable improvement over using a Discone or similar commercial multiband antenna. Since these antennas were first introduced Shakespeare has made a single antenna covering all the same bands (model US-1387) but its much less gain on VHF and UHF. You could do better with commercial broad band repeater antennas but a couple of 21ft tall VHF/UHF and maybe a 15ft tall 800 antenna is not going to work on a lightweight cross arm or fit on most residential roofs.

Anyway, here are pics of the antenna system and triplexer box set together for the first time and it all has to come apart to transport to its final destination. The 10ft mast holding the cross arm is the top piece of a home made 20ft pushup mast that will affix to the new owners chimney with a heavy duty chimney mount.





I have a duplicate set of all parts and someday will put together the same setup on my roof to replace an existing Discone with supplemental 700/800 antenna with diplexer.

 

[mmckenna]

Nice, I'll take 2.

 

[prcguy]

Nice, I'll take 2.

Place your order, pay lots of $$, wait a long time. I think the antennas alone new run around $1k then the triplexer is almost $300. Its nice when you can find all the stuff cheap on fleabay like I did.

 

[mmckenna]

Looking at the options that the big antenna manufacturers have for multiband base antennas, I think you could make a lot of money if you had someone to market them. The offerings from the companies I've looked at are in the $1,500 and up range.

 

[prcguy]

Looking at the options that the big antenna manufacturers have for multiband base antennas, I think you could make a lot of money if you had someone to market them. The offerings from the companies I've looked at are in the $1,500 and up range.

There are other options. I'm currently helping an organization installing some of these for interop. (1Y20850) MADP150-450-816 - Hascall-Denke

 

[mmckenna]

I've looked at their antennas a few times. They usually have a pretty interesting booth at the trade shows showing off their military antennas.

 

[serial14]

@prcguy how do you compare this approach to the build you did in this thread prcguy's mast mount filter/preamp/diplexer thingee

 

[prcguy]

@prcguy how do you compare this approach to the build you did in this thread prcguy's mast mount filter/preamp/diplexer thingee

The mast mount filter/preamp/diplexer was to make use of a Discone and originally intended for receive only but I did put in some bypass relays so I can transmit at low power. The marine antenna setup above is much better for transmitting as the antennas have more gain than a Discone. For receive only the marine antenna setup is very good minus any preamps which helps driving long runs of coax. But since the marine antennas have some gain over a Discone it can work better than the filter/preamp/diplexer in some receive only applications.

 

[VE2XWA]

Over the years I've collected lots of antennas for projects including some nice Shakespeare marine versions used on Govt vessels. I've had the parts laying around for years to make a VHF/UHF/700/800 setup using discreet marine antennas for each band and a commercial triplexer but never got around to putting it all together. Then a friend got some multiband radios and needed something similar so I gave him a shopping list of what I had not expecting him to actually find all the parts. Well he did and I just finished putting together all his parts into a really nice multiband base antenna that would be great for any scanner enthusiast or someone with a multiband radio like Motorola APX8500, Harris XG-100M, etc.

The individual antennas used are the Shakespeare HS-2774-R covering 136-174MHz with 4dBi gain, a Shakespeare US-3849 covering 380-490MHz with 4dBi gain and a Shakespeare 4800 series designed for 800MHz but covers down into the 700 range just fine. All are rated for shipboard use and should never have a problem from weather or corrosion. All antennas are mounted on a 6ft cross arm giving 1/2 wavelength spacing between antennas at VHF and much more at UHF and 800. Right below the cross arm is an outdoor NEMA rated box containing a high power Motorola triplexer and interface cables providing a single feedline to the radio. All antennas and hardware have been primed and painted grey to soften the impact to neighbors. Mast and cross arm hardware are aluminum castings from NuRail.

This setup should provide a very noticeable improvement over using a Discone or similar commercial multiband antenna. Since these antennas were first introduced Shakespeare has made a single antenna covering all the same bands (model US-1387) but its much less gain on VHF and UHF. You could do better with commercial broad band repeater antennas but a couple of 21ft tall VHF/UHF and maybe a 15ft tall 800 antenna is not going to work on a lightweight cross arm or fit on most residential roofs.

Anyway, here are pics of the antenna system and triplexer box set together for the first time and it all has to come apart to transport to its final destination. The 10ft mast holding the cross arm is the top piece of a home made 20ft pushup mast that will affix to the new owners chimney with a heavy duty chimney mount.

View attachment 188707

View attachment 188708

I have a duplicate set of all parts and someday will put together the same setup on my roof to replace an existing Discone with supplemental 700/800 antenna with diplexer.

I'm also working on a project with a Hammond box. Nothing complicated, just a cable in a box big enough to hold an amp, batteries, etc. Outside access to my shack to test / try a temporary antenna.

 

[prcguy]

Update to this project, got all the items to the new owner and the mast with cross arm, triplexer and all antennas are mounted to his chimney using four SS strap mounts provided by the owner. All connectors are covered in hot glue heatshrink and the 20ft pushup mast is nested in the picture below. It will go up another 8ft or so and we decided to add guy wires when the job gets finished next week.

LMR400 will be run into the attic to a two way coaxial relay then to a radio in the house and to another location in the garage where the coaxial switch will be energized by the garage power supply when that radio is on. This setup will provide noticeably more gain from 136 to about 870MHz than any Discone or triband or multiband antenna I know of. I might post a picture next week with the pushup mast extended and guy wires installed.

 

[jeepsandradios]

I really like that Nema box. I ended up running my LMR inside the atic then have the splitter just after polyphaser.