Single & Tri Band Antenna with Diplexer

[K2theFEA]

Hi guys,

I'd like to combine these 2 antennas with 1 scanner:

Laird Technologies WPD136M6C-001
Frequency (MHz) 136-174/380-520/760-870
http://www.theantennafarm.com/catalog/laird-technologies-wpd136m6c-001-4286.html

and

Laird Technologies WPC39S0B-001
Frequency (MHz) 39-46
http://www.theantennafarm.com/catalog/laird-technologies-wpc39s0b-001-6438.html

Can some suggest a few options for a diplexer? I'd like to monitor public safety channels (mainly CHP). I am open to suggestions if you think there is a better way to do it. I'd like to keep things down to 1 scanner if possible.

Thanks,

 

[mmckenna]

That multi-band Laird is a big antenna. The base is 2 or 3 inches around. You can save some money by using one of these:
http://www.theantennafarm.com/catalog/larsen-nmo150-450-800-1050.html

Just my personal opinion, but if you are not going to transmit with it, you can save $50 really easy.

You'd need a diplexer similar to this: http://www.theantennafarm.com/catalog/comet-cf-530-1644.html
But it doesn't mention performance above 470MHz, so not sure how well it would work above that frequency range.

Hard to beat specific antennas for each band.

Other option (sort of) is to use a 5/8th's wave VHF antenna, it'll be 1/4 wave on part of the low VHF band as well as work well on VHF. You could use the multiband for UHF, 700, 800, 900 MHz, too.

 

[K2theFEA]

"Hard to beat specific antennas for each band."

Meaning multiple single band antennas each connected to its own scanner (1:1 ratio)? Or many single band antennas combined to a single scanner?

What if I just went with something like this:

MP Antenna 08-ANT-0865
Frequency Range 25-1300 MHz
http://www.theantennafarm.com/catalog/mp-antenna-08-ant-0865-6616.html

Thanks for the feedback! I'm learning a ton as I go. 5/8th wave is new to me. Everything to this point has been 1/4 wave. Need to do more reading.

 

[K2theFEA]

This diplexer should work on those frequencies:

http://www.theantennafarm.com/catalog/comet-cf-416w-1643.html

Band Pass 1.3-250MHz & 400-1400MHz

 

[mmckenna]

"Hard to beat specific antennas for each band."

Meaning multiple single band antennas each connected to its own scanner (1:1 ratio)? Or many single band antennas combined to a single scanner?

Yes. It's difficult to do with a scanner since you'd need a diplexer that split/combined all the different bands that way. What it gives you in return is the ability to use specifically designed/tuned antennas on the frequencies you want. While having an antenna tuned for just receiving isn't really required, having dedicated antennas that are designed for what you are actually trying to do usually works out better. Multiband antennas tend to do several things is a mediocre fashion, where a single band antenna will do one thing very well.

What if I just went with something like this:

MP Antenna 08-ANT-0865
Frequency Range 25-1300 MHz
http://www.theantennafarm.com/catalog/mp-antenna-08-ant-0865-6616.html

I have not heard any good reviews on those. "All band" antennas like that tend to trade performance for wide useable frequency spread. Usually doesn't work out too well.
Since you know exactly what/who you want to listen to, you'd probably do better with at least 2 antennas. Low band really requires a long antenna to work well. Any of these short antennas are going to be very poor low band performers. You'd do better with either a dedicated low band antenna, or using a 5/8th's wave VHF antenna. Antenna length cannot be replaced. These short antennas like this are just a marketing game.

Thanks for the feedback! I'm learning a ton as I go. 5/8th wave is new to me. Everything to this point has been 1/4 wave. Need to do more reading.

There are a couple of things like this you can do.
A 5/8ths wave VHF antenna performs like a base loaded 1/4 wave low band antenna.
A 1/4 wave VHF antenna performs like a 3/4 wave UHF antenna. In fact, I used to use a 1/4 wave VHF antenna for a dual band (VHF/UHF) amateur radio. Tunes up fine and works pretty well.

800MHz is a bit trickier. It's going to be happy with a proper antenna.

If you can find a diplexer that will split things out this way (probably difficult):
5/8'ths wave VHF for your VHF High and Low monitoring.
UHF antenna
800MHz antenna.

Or, just a low band antenna and a VHF/UHF/800MHz antenna would be easier.

But, for listening to the CHP (I live in California) you really need a long antenna. Dedicated low band antenna or using the 5/8th's wave VHF is going to be necessary unless you are close enough to who you want to listen to.

 

[K2theFEA]

I really appreciate the time you've taken to help me out here!!

More questions

Would the 5/8th wave antenna be even longer than the 1/4 wave antenna? Would the 5/8th wave require a larger or smaller ground plane? Remember this is just for scanning at the moment.

Can I trouble you to shoot me a few examples of a 5/8th wave antenna you think would be a good fit?

Thanks!!!

 

[mmckenna]

A 1/4 wave VHF antenna is going to be about 18 inches long.
A 5/8 wave VHF antenna is going to be about 48 inches long.

Ground plane will be the same, it's based off the frequency. A good rule is to have 1/4 wave length of ground plane in all directions around the antenna. So, ideally, for a VHF antenna, you'd want about 18 inches of metal in all directions under the antenna. Center of the vehicle roof is usually best.
On a low band antenna this is difficult/impossible to do, so you just give it as much as you can. If you look at a CHP vehicle, the longest antenna is the low band antenna. It's usually mounted dead center of the vehicle roof to give it the most ground plane.

A good 5/8th's wave mobile antenna would be the Larsen NMO 150. I've used Larsen brand antennas for 25 years and never had a failure. I've got probably 50 or so Larsen brand antennas on mobile installs at work. They'll cost a bit more than the cheap-o Chinese brands (Tram, Browning, other names I can't spell/pronounce), but they'll last a lot longer.

 

[K2theFEA]

So here's my dilemma and it sounds like you can help me come to a comprise. It's worth mentioning I'd like to skew towards better scanning performance and I don't mind drilling holes if necessary. I'd also like to keep things as aesthetically pleasing as possible

My car isn't exactly an antenna friendly (read ground plane) vehicle. I have 2013 Kia Sorento with the panoramic moonroof. See the image below. I got this before I ever thought I'd want to get into this hobby. Now I'm screwed, lol.

We are tossing around the idea of 2-3 antennas, a di/triplexer and my main frequency of concern is around 42 MHz. I was thinking of putting an antenna on either side of my AM/FM factory antenna. What do you think?

https://s-media-cache-ak0.pinimg.com/736x/35/5c/41/355c413b315a9a3a7722cbbb09bf0e8a.jpg

 

[mmckenna]

Ah, yes. The panoramic sun roof. My wife had a Pontiac that had that. Ended up installing a glass mount UHF antenna so we could put the GMRS mobile in there for her. Worked well enough, not perfect.

Antenna mounting can be dealt with. You might need to get creative, but it's not impossible. Ground plane isn't a huge issue for just receiving, so don't get too hung up on that.

I've done some interesting installs on some vehicles like that, including mounting a VHF 1/4 wave whip in between the sun roof and the windshield.

I think the basic tri-band antenna I linked to above would be perfect for this install. It's only about 19 inches tall, so not a big deal. They are black, so they'll blend in pretty well.

A dedicated low band whip will do best on the CHP stuff. It would be ideal to mount one of those if you can. If you can't, you could try just running the tri band antenna. Won't be perfect, but you'll get some stuff.

The real trick here is finding a diplexer that will let you combine these two antennas into one radio. Unless, of course, you wanted to have two radios. Since CHP is running analog FM on low band, a very basic scanner will work just fine. You might even be able to find one used for less than you'd pay for the diplexer.
Just an idea.

 

[K2theFEA]

Ah, yes. The panoramic sun roof. My wife had a Pontiac that had that. Ended up installing a glass mount UHF antenna so we could put the GMRS mobile in there for her. Worked well enough, not perfect.

Antenna mounting can be dealt with. You might need to get creative, but it's not impossible. Ground plane isn't a huge issue for just receiving, so don't get too hung up on that.

I've done some interesting installs on some vehicles like that, including mounting a VHF 1/4 wave whip in between the sun roof and the windshield.

I think the basic tri-band antenna I linked to above would be perfect for this install. It's only about 19 inches tall, so not a big deal. They are black, so they'll blend in pretty well.

A dedicated low band whip will do best on the CHP stuff. It would be ideal to mount one of those if you can. If you can't, you could try just running the tri band antenna. Won't be perfect, but you'll get some stuff.

The real trick here is finding a diplexer that will let you combine these two antennas into one radio. Unless, of course, you wanted to have two radios. Since CHP is running analog FM on low band, a very basic scanner will work just fine. You might even be able to find one used for less than you'd pay for the diplexer.
Just an idea.

So I think I'm going to take a hybrid approach. I'll probably end up with two scanners one dedicated to VHF Low and another, using a diplexer or triplexer for VHF and UHF. I don't think I'm going to jump into it all at once. I'll probably start with the VHF Low antenna and work my way up to the final setup. Considering the fact that the VHF Low will be the tallest of the whips (unless I end up getting a CB) do you think I should remove my stock AM/FM antenna and replace it with the 64" Laird whip? It's the highest point on the car with a "respectable" ground plane (nothing like the middle roof of a Crown Vic; remember I'm moonroof challenged). I thinking I can always relocate the stock AM/FM antenna somewhere else. My girlfriend likes to listen to FM and enjoy AM news radio otherwise I'd ditch it altogether. I wonder if I can fit an NMO mount where the stock antenna is located?! That would give me some time to procrastinate the eventual drilling I'll need to do.

 

[miserytom]

For just RX with a scanner you really don't need all the extra equipment your looking at , I have a home patrol and a basic 15" NMO antenna on the car and I get everything 30 mhz -900mhz from 40 miles away no problem

Sent from my SM-G920T using Tapatalk

 

[mmckenna]

I'd leave the stock AM/FM antenna where it is. You'll likely have a very hard time fitting any sort of NMO mount in the existing hole. Anyway, while I'm all for doing a proper install, annoying the girlfriend/wife/significant other is never a good idea. Some things are more important than radio.

I'd recommend mounting the low band whip on the opposite side of the hood. Use one of the bracket mounts that mounts in the fender/hood channel. It's a simple little bracket that screws in place. Mount it opposite the AM/FM antenna. Won't look stock, but it'll look about as good as possible in my opinion, short of going center of the roof (I know, not an option).

Tom brings up a good point. For one antenna, the tri-band might be good enough. It'll have dismal performance on low band, but it will pick up -something- while giving you access to VHF/UHF and 800MHz. Might be worth giving it a try. Maybe do the fender bracket mount and try both antennas. The longer whip _will_ work better for CHP low band, no doubt there. There is no replacement for metal in the air when you are working lower frequencies.

 

[mmckenna]

So I think I'm going to take a hybrid approach. I'll probably end up with two scanners one dedicated to VHF Low and another, using a diplexer or triplexer for VHF and UHF.

If you are going with two radios, skip the diplexer. It'll just add unnecessary loss to the system. The tri band antenna I linked to above will work just fine for VHF High band (it "looks" like a 1/4 wave to the radio), UHF (looks like a colinear to the radio) and 800MHz to the radio. You could install one mount and just this antenna and it'll work well. One of the nice things about living in California is our topology. With all the hills/mountains around us, most radio systems rely on mountain top repeaters. If you look at most public safety vehicles you'll see quarter wave antennas as the predominate choice. That's because the systems are designed for mobile radio coverage using a quarter wave antenna. Usually you can take a look at what the agencies are using and design your antenna system the same and it works pretty well. Once you get outside their area, things suffer as the systems are only designed to cover a certain area, but it'll still work. Since you are in SoCal, you shouldn't have much problems.

Still, Low Band is really picky. While you can get some useable signal on a shorter antenna, it's not going to work well, especially if you head out into the mountains. Heading out east of your area is really going to be an issue. CHP uses a lot of simplex, in other words, no repeaters. A lot of their radio traffic is car to car or car to base. Since they are not using repeaters, relying on a high radio site to make up for your limited antenna system doesn't work well. You'll really get much better performance for a dedicated antenna.

A CB whip is going to be roughly the same size, so keep that in mind with your installation. You can get NMO mount CB antennas. Larsen NMO-27 was always my favorite when I still had a CB in my. It'll look similar to your low band antenna. Mounting it is going to be tricky if you put your low band scanner antenna in the one good space.

It's tough to figure out these antenna placements, especially when you have the panoramic sun roof to deal with. I've always made it a point to not order sun roof's on any of my trucks. My wife does have a Ford Escape that has one, but it's only got the VHF mobile and a single quarter wave antenna to deal with. Plenty of room on that vehicle to mount it. towards the rear with plenty of ground plane left to spare.

If you ever decide to replace your vehicle, you'll find yourself looking at it with antennas in mind. Sort of one of the risks of the hobby/industry. Antenna installation is important, and your needs might dictate the vehicle design/options.

 

[mmckenna]

I think I may have assumed you were in Southern California, sorry if I was off the mark. I'm up near Monterey, but do travel all over California pretty regularly, so I'm familiar with most of the state. Let me know where you are located (roughly) and I might be able to provide more info.

 

[cmdrwill]

For starters go with a single NMO mount 1.4 wave, 18", whip and see how that performs in your area.

 

[K2theFEA]

I think I may have assumed you were in Southern California, sorry if I was off the mark. I'm up near Monterey, but do travel all over California pretty regularly, so I'm familiar with most of the state. Let me know where you are located (roughly) and I might be able to provide more info.

I live in San Jose but I regularly travel all over the bay area. I go to Petaluma and Santa Rosa on occasion. Monterey and Santa Cruz from time to time. During the winter I do about a dozen or so trips to South Lake Tahoe. Once every 3 to 6 months I'll drive to Los Angeles. There might be a few trips to Reno, Las Vegas and Utah but that should pretty much summarize my driving habits My lower back has been killing me lately so longer trips in the car are tougher than they used to be. Before the the back all I had to worry about was keep the speed below a certain threshold. Now my nagging back makes me want to get to the finish line sooner rather than later

 

[K2theFEA]

For starters go with a single NMO mount 1.4 wave, 18", whip and see how that performs in your area.

On UHF I get decent signal in the car using a telescoping antenna (it's okay to laugh at me). I'm really tempted to start with the Laird 64" or 49" Larsen whips to boost my performance around 42 MHz. If I'm understanding @mmckenna correctly I should have either one of those antennas mounted to the fender/hood channel with the appropriate bracket mount. If I do that, do I go driver side or passenger side? Closer to the windshield or front of the car? Btw, mounting on the hood/fender has the added benefit of better overhead clearance. Shucks, I might even be able to get in and out of my garage

 

[mmckenna]

Ideally you really do want it mounted in the center of the roof, but that's obviously out of the question.

Doesn't matter what side it's on. Usually work a bit better if you keep them away from other metal, especially other antennas. While you won't be transmitting, it's still a good idea to keep some separation. I wold mount it on the opposite side than the AM/FM antenna, partially for aesthetics, Partially to prevent any issues with the other antenna.

UHF will work inside a car because the wavelength is smaller. One of the benefits of UHF is that it penetrates buildings better than VHF. 800MHz does even better.
Performance will improve across the board by just getting an external antenna.

1/4 wave VHF might be a good place to start. They will work well on VHF and UHF, as they are 3/4 wavelength on UHF. Probably not going to work well on 800, and too short for low band, but it'll still work better than an antenna inside the vehicle. Just too much metal surrounding it to work well. Add tinting on the windows, which sometimes contains metals, and it's even worse. If you are halfway happy with the antenna inside the vehicle, then you'll probably be really happy with any antenna outside the vehicle.

Still, like I've said, it's really hard to beat band specific antennas, especially on low band.

I'm actually in Watsonville, and I work in Santa Cruz. I grew up in San Jose, lived there into my early 20's. Not sure what made me think you were in LA, must have been thinking of something else. No offense intended.

 

[K2theFEA]

I'm actually in Watsonville, and I work in Santa Cruz. I grew up in San Jose, lived there into my early 20's. Not sure what made me think you were in LA, must have been thinking of something else. No offense intended.

Hahahaha, none taken! Thanks for the continued support and advice.

So I'm more than likely going to run with your suggestion and leave the AM/FM antenna where it is. But...I stumbled on this bad boy and it got my mind running (that's how I usually get in trouble):

PCTEL Maxrad GPSPSM
Frequency (MHz) 27 - 2400 MHz (Antenna Option) / 1575.42 (GPS)
http://www.theantennafarm.com/catalog/pctel-maxrad-gpspsm-3355.html

My Uniden BCD436HP supports GPS and I was wondering if I could use the GPS antenna that comes with this mount. I think it's super cool that this mount has the GPS antenna built in and it support an NMO style antenna. If I'm only receiving, I'm thinking it won't be such a big deal if 2 antennas are this close to each other. Then again, I'm the noob, you tell me. I doubt it will because the scanner GPS port uses a funky micro USB connector.

Another question I have for you with respect to lip mounts, bracket mounts and the whole ground plane issue.

A) I feel like all the mounts end up doing a certain amount of damage to the car. The bracket mounts require some drilling but I guess most folks feel better about it when they can't see the holes.

B) Since the 1/4 wave whip requires a ground plane will the bracket/lip mounts suffice?

I guess I'm really overthinking this especially if I'm not planning on transmitting anytime soon. I should probably do less typing and more experimenting but the perfectionist in me (and I'm trying to save time/money) pushes me to do more homework.

Thanks,

 

[mmckenna]

Yeah, that would work.
It's a plain old NMO mount with a GPS antenna built into the base. My brother in laws work vehicle has something similar on the roof, but with a cellular antenna. There's a box under the dash that takes the vehicle GPS position, speed, etc. and sends it via cellular back to his employer.

Anyway, one of those would work fine, but it is -just- the GPS antenna in there, not the whole receiver. I honestly don't know how those scanners work, do they have a built in receiver with an antenna jack, or just a serial/usb port of GPS data? If it's just the serial port/USB port, you'll still need a receiver with an antenna jack.

Trouble with these is the mounting. They are designed to go through a hole in the roof, so mounting is going to be difficult. Mounting this off the side of the hood is going to be problematic due to the longer base depth. Might work better if you mounted it on the roof with a tri-band antenna.

For the hood bracket mount, you can use something like one of these:
http://www.theantennafarm.com/catalog/mobile-antenna-mounts-264/fender-bracket-mounts-268/