Best cable for mobile discone

[PropHumm]

Ok, thank you for the insight on the dual CB antenna setup. I've spent the evening looking closer at the actual db gains compared to losses. I can see now that potential gain is nominal from the extra antenna, but potential losses could be extensive. I actually had the co-phased coax figured out and in hand but that doesn't matter. I am more concerned with performance. Now I start over with a single CB antenna. This will make it 3 antennas fighting for that prime center of the roof location, keeping in mind that the spare tire reduces the available space considerably.

 

[mmckenna]

This will make it 3 antennas fighting for that prime center of the roof location, keeping in mind that the spare tire reduces the available space considerably.

Pretty sure that truck is bigger than my first apartment.

One way to look at this is to consider how cable losses will play in. I usually plan out my antenna installs carefully.
Getting a proper ground plane under the antenna should be high on your list of priorities.
The CB antenna wants to see 8 foot radius ground plane under it. That's not going to happen on a road legal vehicle. But putting the antenna as close to the center of the roof is the best you can do. That may put it farther from your radios, but since it's a lower frequency, coaxial loss will be lower.
I rarely use CB, but when I do, I use the same Larsen NMO-27 I've owned for 30 years. You won't find a better CB antenna. Add a spring base, and it'll handle whatever you can throw at it. Mine has been through lots of parking garages and hit a lot of low branches. With a good ground plane, it'll tune down nice and low and flat across the CB band. I had mine on the roof of a full size crew cab pickup and I had no issues with it. It worked very well.

For the 2 meter/70 centimeter band, Larsen makes a few dual band antennas that work well (NMO-2/70 and NMO-2/70SH). There's a long ~40" or so version that works well, and they also make some lower profile ~20" versions. The shorter ones come with a spring base. The longer ones can have it added. Those antennas will want to see about 19" radius of ground plane under the base. Fairly easy to do on a big vehicle like that. I'd install it about 2 feet back from the front of the cab roof. That'll give you a nice ground plane, and should put you well in front of the CB antenna.

Cell and GPS antennas are easy since they don't need much ground plane. Again, NMO bases will handle both, although the GPS antenna may want the NMO-HF mount which is a bit different than the standard NMO mounts and work a bit better at higher frequencies. Doesn't take much of a cell antenna outside the vehicle to really improve performance. I used to have one in a truck and I had a shark-fin style cell antenna that worked very well.

Spare tire shouldn't be an issue, other than the physical space. While there are steel belts in the tire and the steel/aluminum wheel is a reality, it won't impact the CB antenna performance.

 

[PropHumm]

I know with the dual antennas, the phasing was critical and cable lengths were key. With the single, is there a preferred length or is the shortest possible length best?

 

[a417]

I know with the dual antennas, the phasing was critical and cable lengths were key. With the single, is there a preferred length or is the shortest possible length best?

shortest reasonable length, the less loss over distance traveled. If you read a product sheet for cable some time, you will see how it references loss over usually 100'. You're probably not going to be anywhere near 100' in that, but if you're looking for peak performance, don't shoot yourself in the foot. Leave a couple extra inches for chassis/body flex, recapping an end or to get around sharp edges, but I wouldn't go and leave 50' coiled under a body panel just because you didn't want to cut it.

[edit]



this is a snippet from times microwave LMR-200 cable to help you with signal loss/distance. (not specifically advocating for this cable, but it was the PDF on my desktop.)

 

[mmckenna]

I know with the dual antennas, the phasing was critical and cable lengths were key. With the single, is there a preferred length or is the shortest possible length best?

Least -reasonable- amount of coaxial cable to get from your radio to your antenna. Leave a foot or so in case you need to install a new connector, an extra foot isn't going to hurt. Route it carefully, but make sure it's protected.

The B.S. that some spout about needing a certain length of cable comes from using precise lengths of cable depending on frequency being able to alter what the radio sees as impedance. If the antenna is tuned correctly, none of that is required. Even when it does work for specific applications, it needs to take into account the velocity of propagation of the cable, which most people don't consider when doing this.

 

[mmckenna]

The B.S. that some spout about needing a certain length of cable comes from using precise lengths of cable depending on frequency being able to alter what the radio sees as impedance. If the antenna is tuned correctly, none of that is required. Even when it does work for specific applications, it needs to take into account the velocity of propagation of the cable, which most people don't consider when doing this.

To paraphrase/clarify this...
You can use specific lengths of cable to 'hide' bad SWR from a radio. It can be quite effective and people that don't understand how it works will claim it makes the system work correctly. Reality is that if you have a properly installed antenna that is tuned for the installation, it's not required. Hiding the issue doesn't magically fix the antenna, it just make the SWR look good from the radio end. The antenna won't work well, though.

 

[PropHumm]

Thank you for clarifying cable performance vs losses over length as it applies to my application.

 

[majoco]

I know with the dual antennas, the phasing was critical and cable lengths were key.

Yes, it does, but you don't want to be moving antennas around on your rooftop depending on the frequency in use

 

[dlwtrunked]

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.

Despite what non-owners will tell you, the D220R is a very good broadband antenna on a car roof. I had one there for years and only removed it because of the attention it received by guards when entering high security government parking lots. A couple times they debated if they would let me in (true story).

 

[PropHumm]

Are there any thoughts on keeping one antenna for just scanner reception (thru multiplexer to several scanners) and another for transmitting with my dual-band? Or is there no difference if I use one for both receiving and transmitting?

 

[mmckenna]

Are there any thoughts on keeping one antenna for just scanner reception (thru multiplexer to several scanners) and another for transmitting with my dual-band? Or is there no difference if I use one for both receiving and transmitting?

If you are transmitting, you'll need to have that on its own antenna. Scanners can be combined on to one antenna with an appropriate multicoupler.

 

[KOK5CY]

Make sure not to use RG58 dual shield . it's basically junk . I bought a nmo 3/4" coax kit for a home in door base using a 18" mobile whip and it didn't work on my bct15x or my grecom psr 600 . dual shield is junk .

 

[mmckenna]

Make sure not to use RG58 dual shield . it's basically junk . I bought a nmo 3/4" coax kit for a home in door base using a 18" mobile whip and it didn't work on my bct15x or my grecom psr 600 . dual shield is junk .

Dual shield is just fine. I've used it on a number of installations. It's good in high noise environments and has a bit less loss.
If you buy cheap antennas/cable, yeah, you'll get junk. But Larsen and a number of the big manufacturers sell dual shield RG-58.

 

[ra7850]

Despite what non-owners will tell you, the D220R is a very good broadband antenna on a car roof. I had one there for years and only removed it because of the attention it received by guards when entering high security government parking lots. A couple times they debated if they would let me in (true story).

How did you mount that antenna on the roof of a car? Custom mount of some type?

 

[PropHumm]

How did you mount that antenna on the roof of a car? Custom mount of some type?

I think there is a misconception on this particular discone antenna. It is not a large base antenna. The Diamond D220R is a mini discone antenna designed for mobile use. It measures 35.5" tall and weighs .8lbs. The base of the antenna is a PL-239 and directly accepts SO-239 mounts, so it is not that different from most mobile single mast antennas.

 

[iMONITOR]

I think there is a misconception on this particular discone antenna. It is not a large base antenna. The Diamond D220R is a mini discone antenna designed for mobile use. It measures 35.5" tall and weighs .8lbs. The base of the antenna is a PL-239 and directly accepts SO-239 mounts, so it is not that different from most mobile single mast antennas.

Right. Here's a couple pictures:

 

[mmckenna]

I think there is a misconception on this particular discone antenna. It is not a large base antenna.

No misconceptions, many of us have seen them in the hamster fest parking lots.

As for an antenna….
UHF plugs don't make good antenna mounts. The shielded banana plug connector was never designed for mobile antenna mounting.
They also tend to sort of suck loudly above 300MHz.

The 'discone' part of the antenna is only going to be good at higher frequencies, where UHF connectors do the loud sucking noises. Essentially it's an elevated feed antenna with a really small discone at the base. The discone elements probably act as a bit of a ground plane on higher frequencies.

Do they work? I'm sure they do, no reason why they shouldn't. Heck, I can make a paper clip into a halfway decent antenna.
Are they going to work well? I'm sure it works well on the ham bands. I don't think it's a magical antenna that's going to out perform anything else. It's marketing gimmick is that it takes two different antenna designs and combines them. Most hobbyists know discones, so are attracted to them. Until I see a side by side comparison done on the same vehicle in the same location, I'm not believing any of the hype. I'll point out that the 'scantenna' was thought to be a bit of a joke until @prcguy did some real world testing with it and found it actually worked fairly well. So, we can always be proven wrong.

Speaking of attracted to them, they usually get snickers at the ham fests. They are considered a "Hey! Look at me!" antenna. Some people like that, some don't. Count me in the "don't" category. Your opinions are likely different than mine. Not my car, not my antenna, you do what you want. Don't pay attention to the random stranger on the internets.

If that's what you want, then it's the perfect antenna. If you want something that's going to work well, there are other and better options. The small size of the discone may work well up in the 800MHz band, but remember, discone antennas have 0dB gain, so a dedicated 800MHz antenna can be had with 3-5dB gain, and it'll be smaller and work better, not to mention look less dorky (my opinion).

For dual band ham use, you can get the same effect, and probably better at that, by doing a permanent mount NMO (over a proper ground plane) dual band antenna like the Larsen NMO-2/70. The ground plane provided by the discone elements are not big enough to act as a ground plane on VHF.

 

[prcguy]

Maybe you meant the COMPACtenna?

I'll point out that the 'scantenna' was thought to be a bit of a joke until @prcguy did some real world testing with it and found it actually worked fairly well. So, we can always be proven wrong.

 

[mmckenna]

Maybe you meant the COMPACtenna?

Yeah, that's what I meant. Something-tenna….

So, if @iMONITOR sends you a free antenna, you'll put it on your home antenna range and give us a report, right?

 

[prcguy]

If he does, and I do, and he tells me its ok to tell you, then yes.

Yeah, that's what I meant. Something-tenna….

So, if @iMONITOR sends you a free antenna, you'll put it on your home antenna range and give us a report, right?