Best cable for mobile discone

[PropHumm]

I am building a chase vehicle for extreme newsgathering. For my scanners, I have 1 SDS200, 2 BCD996P2's and 2 BCT15x's . . and will be adding at least 2 more SDS200's in the next couple months. My choice for antenna was the Diamond D220R Discone to cover all the frequencies and feed all the scanners with the single antenna. I am getting ready to purchase a Stridsburg MCA208M 8 port multicoupler to feed the scanners. I have options for the output connectors, being TNC, N, or BNC. My thought was to go with BNC because of the scanners having BNC jacks. Where I am not sure is what cable I should use.

 

[cg]

That would be... interesting... to have a large discone on a vehicle. Unless you are outfitting a semi truck, your cable runs will be very, very short. You can use a good quality BNC/BNC jumper. Pomona is a bit pricey but very good quality. You can spend anywhere from $5 to $125 per 18 inch jumper.
I personally would look at several mobile antennas targeting certain bands and use a couple 4 port Stridsbergs.

chris

 

[wtp]

he looks new here, so he will probably put the antenna inside the vehicle where it would be safe...

 

[vagrant]

1. Larsen NMO 150/450/758 antenna - That covers the frequencies where the action is and it is better than that discone.
2. LMR-240UF - This coaxial cable is thin and flexible enough for long or short runs with lower attenuation. UF = Ultraflex
3. Depending on where you are, you may need to put an FM broadcast filter inline on the coax from the antenna. FM radio stations are not a scanner enthusiasts friend. Pager signals around 152 MHz can also be a problem, so you may need to add a filter there too.
4. BNC is fine. Make sure you do not go cheap on the BNC patch cables. You will get what you pay for, even if they are short jumpers. Beware!

That will be quite a few scanners. I presume you will dedicate each one to a particular service, or maybe two for local PD and the others for Sheriff, Fire and perhaps State Police. I'm figuring you will also monitor a nearby city/suburb as well, or perhaps local metro PD. Tell us more.

 

[prcguy]

I would not use a Diamond D220R for public service monitoring, I believe its top whip is tuned to the amateur bands and the Discone part probably doesn't come into play until 400MHz or higher. As mentioned, a Larsen tri-band would probably work better. Or a Laird WPD136M6C or a Maxrad BMAXSCAN1000 or a Comtelco, bla bla bla.

All these resonate within the VHF/UHF/800 public service bands at the minimum and a few like the Laird work fine in the 2m, 70cm, 23cm amateur bands. Then there is the COMPACtenna Scan III which is no slouch and covers a good chunk of the VHF/UHF/700/800bands very well. I believe any of these antennas will work much better and more consistent than a Diamond D220R for chasing sirens, uhhh, I mean, news gathering.

As for cable, it depends on how long the run is. Again, as mentioned, Times LMR-240UF would be one of my first choices and if the run was very short like under 10ft maybe LMR-195 and this is for the run from the antenna to the multicoupler. If the runs are short from the multicoupler to the radios, like 2ft then I would use a good quality RG-58 or LMR-195 because the multicoupler has extra gain per channel and you can afford a little loss in the cables to the radios.

 

[PropHumm]

Yeah I can share all of this! What Forum would be best for posting my chase vehicle build?

 

[vagrant]

Probably just stay with this thread. A moderator will move things if necessary, but your buildout here seems appropriate as you take whatever advice, or not, and move forward it. They may just change the title to better fit.

 

[mmckenna]

Please don't install that antenna and expect anyone to take you seriously as a news gatherer.
That's a joke of an amateur radio antenna, and a poor joke at that. They are the antennas that people point and laugh at when you see them in the parking lot at the local ham fest. Yes, we do, and I have, many times.

Use one single Larsen NMO-150/450/756 on a permanent mount NMO base mounted smack in the middle of the vehicle roof. Do it right, do it once, and you won't regret it. Don't cut corners with cheap Chinese/hobby/amateur grade antennas, mounts, connectors, etc.
If you are in an area that uses low band VHF, consider adding a dedicated low band antenna and connect it to a dedicated radio.

Run that antenna to your multi-coupler and split it off to all your radios's's's's's's's'…...

The standard RG-58 that comes with the NMO mounts will work fine. You are not going to have enough cable length to be a problem, unless you are driving a Greyhound bus and want to mount the antenna on the rear and your radios up front.

 

[PropHumm]

Ok, I've been busy removing the interior. Now back to the antennas and wiring. Here is a picture of my roof rack. I have to position dual CB antennas (Wilson 2000), scanner antenna (Diamond D220R mini Discone), Kenwood TM-D710G, which I have not decided on an antenna as of yet, cell booster antenna, and GPS booster antenna. The CB, Kenwood, and scanner antennas will be retractable. I am building power up/down mounts for each. Please excuse the orange strap. It is a makeshift until I get my hold down bracket made. I am thinking I will mount the 2 CB antennas on each side of the spare tire,, with the coils just above the tire. I don't like the fact that my mount will need to fold the forward to retract them. The scanner antenna in the center, right behind the sunroof. The GPS and cell antennas on each side of the sunroof and no idea on the Kenwood. Any input on placement would be appreciated.

 

[mmckenna]

Why do you need to fold the antennas down?

If you have enough clearance for the spare tire, you should have enough clearance for the antennas. Fabricating a fold down mount is cool and all, but if you want performance out of these antennas, you need to make sure they have a good ground plane under them.

And forgive me for asking, but why two CB antennas?

Placement needs to consider the required ground plane for the antennas. Ideally your CB antenna(s) need to go on the center line to get the most amount of ground plane under them. Putting them off to either side is going to result in a lopsided radiation pattern.

Cell booster and GPS antennas won't need much ground plane, maybe 4 inches around the base. You could stick that in one corner of the front of the cab. That would also keep the coax runs short. At the higher frequencies used by GPS and cellular, the coaxial losses will be higher, so best to keep those cables short.

The 2/70 ham antenna could go off to one side if you had about 19" of space around the antenna, so 19" in from the side of the roof.

 

[PropHumm]

Why do you need to fold the antennas down?

Making the antennas fold-down serves 2 purposes. First, it would allow me access to lower clearance areas without extra punishment on them. The second reason is to be able to be a little more discreet with them, hopefully lessening them as a target for vandals or getting them stolen. I find myself in some precarious situations, not to mention bad areas. I'm aware it will create some ground plane challenges and am hoping to come up with ideas to lessen the impact.

 

[PropHumm]

And forgive me for asking, but why two CB antennas?

When I was researching equipment, I came across information that showed that dual antennnas side by side would distort the pattern, making it oblong, increasing the forward range 2-3 miles over a single antenna installation.

 

[mmckenna]

When I was researching equipment, I came across information that showed that dual antennnas side by side would distort the pattern, making it oblong, increasing the forward range 2-3 miles over a single antenna installation.

True, but that only works if you have sufficient separation between the antennas. You won't get that separation on that vehicle. It works on big rigs when they mount them out on the mirrors, but anything smaller than that just makes a mess of the pattern.

One antenna installed properly and tuned correctly will make for better performance.

 

[mmckenna]

Making the antennas fold-down serves 2 purposes. First, it would allow me access to lower clearance areas without extra punishment on them. The second reason is to be able to be a little more discreet with them, hopefully lessening them as a target for vandals or getting them stolen. I find myself in some precarious situations, not to mention bad areas. I'm aware it will create some ground plane challenges and am hoping to come up with ideas to lessen the impact.

OK, I don't disagree with that, but a truck like yours is going to draw a lot more attention than a few antennas will.

For what you are doing, NMO mount antennas will spring bases will do fine in areas with low branches. If parking garages are part of the plan, then you may want to remove them. The cell antenna will only be a few inches tall, and shouldn't be an issue in a parking garage, it'll be lower than your spare. The dual band and CB antenna can be easily removed.

Having a proper ground plane under the antennas will make for much better performance. While I understand the idea behind the fold over mount, it's going to make getting a full ground plane under the antenna mount very difficult.

I have a 1/2 wave VHF whip on my Polaris Ranger. A few weeks back I was able to drive through a culvert under some railroad tracks where I had about 3" of space above the roll cage. The antenna folded all the way back 90º at the spring, and bounced right back no issues.

Ground planes and proper antenna install really does make a large impact on performance. You could make this work, but you'll need to pay careful attention to the design. Remember that DC ground is different than an RF ground plane.

 

[K9DWB]

I used to run tractor trailers AKA 18 wheelers for an 11 year span career. I did all my own installs and SWR checks, etc. Dual antennas on the mirrors was just enough separation IMO to work as designed to modify the radiation pattern to bias front/rear of the vehicle. Later, when I tried a single driver side only CB antenna, I was pleased with it being better balanced. In your case, I'd do a single antenna as close to center of the roof as possible. Dual antennas are not going to have enough separation in your situation, again IMO. I personally think a single antenna is twofold win, better performance and less work and money to install and purchase 1 vs 2 antennas.

 

[PropHumm]

I was working off information that specified a minimum spacing of 60" for a dual CB antenna installation. I would be 61" so I figured that would give me the full performance. I guess I didn't consider the minimum distance as giving less performance than what they showed in their graphs.

 

[hill]

I agree on not mounting this antenna on any vehicle. I have saw hams using these kind of antennas a few times and they look out of place, plus really stand out. The wind load on the highway would be kind of high. If you were news gathering in the area of high crime Baltimore City someone would likely yank off this large antenna.

Going forward use 1/4 wave antennas for whatever bands you need to monitor, as they work great and are low profile.

I drive a much smaller vehicle than you, but my VHF 19", UHF 6" for ham DMR and 700/800 3.5" for PS with the scanner antennas really blend in.

 

[iMONITOR]

I'll chime in the Diamond D220R, some of you know I had one some time back and spoke well of it. I also got the same criticism from about a dozen people here on RR but as it often happens none of it came from people that actually owned one or even tried one. I don't think those judging it at the time even understood how it's made. There weren't sure if it was a discone or a ground plane. Interesting to note the lower elements are not just metal rods. They're actually made of a material similar to fishing rods that have some flexibility. They had a fine wire wound on them almost their total lenght giving them totally different RF properties than one might originally think. Half of these elements are also a different diameter than the rest. All the reviews I read other than here on RR were very good, especially on 2m/70cm amateur radio, for receive AND transmit.

My hopes that it would be a suitable antenna for a dual-band VHF commercial and UHF military aircraft antenna. I liked the small form factor as it was going to be use temporary inside my home office. ( I found wtp's comment funny)! I think there's been several people here on RR buy them as well, maybe we'll hear from some of them. It worked very well for my needs at the time and I was not disappointed.

There is a similar clone of the Diamond D220/D220R, the Harvest D220 and you can find them on Amazon, Ebay and several other sites. The original Diamond D220 and currently the Harvest have two small loading coils within the vertical element. The latest Diamond version D220R do not have these coils but the added a different coil wound within the element itself.

 

[PropHumm]

Ok, question on the dual CB antennas . . . does the close spacing effect reception in any way? When transmitting, what is the effect of the close spacing? does it make the pattern more oblong or does it distort it entirely?

 

[mmckenna]

Ok, question on the dual CB antennas . . . does the close spacing effect reception in any way? When transmitting, what is the effect of the close spacing? does it make the pattern more oblong or does it distort it entirely?

I would impact reception.
As for the pattern, it would be something to look at on a simulation program, but I doubt it would be a beneficial pattern.

One antenna dead center of the vehicle is your best bet. You don't have enough width to get the front/rear pattern like on the trucks.

The other challenge is that the phasing harness needed to make the dual antennas work correctly requires 75Ω cable, and I'm not aware of any NMO mounts that come with 75Ω coax. You could build your own, but again, with less than 1/4 wave spacing between antennas, it's likely not going to be a favorable radiation pattern.