Using 2 Mobile Antennas with 1 Scanner

[rmcclellan]

1). Let's say that I wanted to have 2 mobil mounted antennas on my vehicle (1 tuned for the aircraft band and 1 tuned specifically for 800MHZ).

I do not want to use a single "all band coverage" <yea, right> antenna since these are mediocre at best.

Has anyone ever tried this? I was thinking about using one of those BNC T-Connectors so both antennas can be attached to the scanner at once.

Is this a NO-NO? If so, is there a better way to connect 2 antennas to 1 scanner? Or, is it just a plain NO-NO period?
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2). Also, had another question about a similiar scenerio:
I was also considering sharing an 800MHZ / GPS combo antenna (Single antenna with the coax being split into 2 seperate runs to each device).

Any ideas, concerns, cautions, recommendations, etc... about either of these two questions would be greatly appreciated

Thank you in advance for the professional advice!

 

[MacombMonitor]

Believe it or not, this will probably do the job just fine!

Valor PMM3B
http://www.universal-radio.com/catalog/scanants/1190.html

 

[SCPD]

Take a look at Ham Radio Outlet, Amateur Electronic Supply, or some other ham radio product dealer. Look for a device called a duplexer. I've used them in the past with several of my mobile ham radios. The Diamond and Comet brands are the only ones I've used and the other brands are probably good also.

 

[TeRayCodA]

Yes,I have tried this before.out of curiosity,and it did work well.
I ran a common catv splitter to a 18" whip(VHF),and to a 6"whip(UHF)
I liked that setup so well,I kept it for a while,until I got a MONR-52 antenna.

 

[BoxAlarm187]

There are a lot of folks that have had good results with the Radiall-Larsen multiband antennas.

However, there is probably some information in this thread that might interest you.

Hope this helps...

 

[Al42]

There are a lot of folks that have had good results with the Radiall-Larsen multiband antennas.

I swear by them - I've been using them since Larsen started in business, but the 2/70 and 150/450/850 aren't that great on aircraft. Good, but a quarter-wave whip is better.

 

[K5MAR]

That would be because the 5/8 wave antennas derive their gain from "focusing" their TX/RX in the horizontal plane. A 1/4 wave antenna has better receptivity in the vertical.

Mark S.

 

[OpSec]

IMO, if you use a Larson NMOQ 2/70B dual band NMO mount antenna for mobile scanning anything 118-800 MHz and you won't be disappointed. There are no wrapped loading coils or matching networks to create signal losses, and it's only 19" tall. This is not the same NMO 2/70B antenna that others mentioned...the NMOQ is the 1/4 wave version of the base loaded NMO 2/70 dual band gain antenna.

For VHF High/Low and aircraft, use a Larsen NMO-150B...it has great RX on everything from 30MHz to 174MHz. I've used one for civil aviation and VHF ham transcievers with great results. It even hears some SWL and ham HF activity, but not well.

For SWL and HF (whatever a scanner can hear, anyway) try using either a Larsen NMO-50B or NMO-27B. The first is a VHF Lowband antenna, and the latter is a CB antenna. I've tried both and they seem to perform the same...okay, but not great. Once you start getting into the low freq's, all mobile antennas start to suck due to the physical 1/4 wavelengths at play.

 

[bluesman905]

For a time I was running two antennas using a BNC "T" to a single scanner and had pretty good results. I have since added a second mobile unit and have dedicated antennas (the same two that were previously split) and the reception has improved somewhat but overall I feel it was still okay to have 'em split. Many people will argue this point but I have seen more people say they have had good results than bad.

 

[Al42]

That would be because the 5/8 wave antennas derive their gain from "focusing" their TX/RX in the horizontal plane. A 1/4 wave antenna has better receptivity in the vertical.

Oops. I was talking about picking up ground transmissions. The Larsen antennas aren't 5/8 wave on 122 MHz, they're closer to ... uh ... who knows? (I've never actually measured one but I expect it wouldn't look much better than the stock ducky at aircraft frequencies.)

 

[Randall]

dont confuse horizontal and vertical planes with polarizations, the 5/8th wave antenna will have more gain on vertical polarized signals than the 1/4th wavelength vertical will but the vertical antenna has a higher angle of radiation.The gain of the 5/8 wave vertical antenna is achieved by the change of pattern that brings down more of the radiation to a lower angle ,closer to the ground.

 

[K5MAR]

Can't find where anybody did.

Mark S.

 

[kb2vxa]

WOAH horsie,

Before the poor guy is confused beyond redemption please allow me to clear up this mess beginning with some serious misinformation.

"Take a look at Ham Radio Outlet, Amateur Electronic Supply, or some other ham radio product dealer. Look for a device called a duplexer. I've used them in the past with several of my mobile ham radios."

The word is diplexer, a duplexer is a set of tuned cavities that separate the input from the output of a repeater allowing it to transmit and receive at the same time on the same antenna, full duplex mode. A diplexer for the ham bands doesn't even come close to 800MHz which is that very critical band in question. I'm working on getting one just for that purpose and I'll keep you posted.

Meanwhile I'm using an ordinary and very cheap (around $5) CATV signal splitter hooked up backwards as a combiner. It works as well as any made for scanners at more than 10 times the price because it's got the same thing inside the box, a simple ferrite tube with a couple of wires through it going in opposite directions. This configuration provides optimum coupling at constant impedance (it doesn't care about 50 or 75 ohms) with the usual 3dB insertion loss. Between the output (or in this case input) ports common mode decoupling provides more than 20dB isolation.

Now the reason for the commercial transmitting diplexer I'm working on is it separates the 800-1300MHz port from the 0-500MHz one (crossover at 600MHz) completely by means of filtering eliminating some awkward phasing effects between signals on the same frequency coming from each antenna. No, an 800MHz antenna still picks up other frequencies well enough to cause some minor problems. BTW, < 0.5dB insertion loss and > 45dB isolation sure beats the hell out of those consumer grade appliances and makes ordering from Denmark worthwhile.

 

[SCPD]

No.... THE device I was talking about is a DUPLEXER. There are also TRIPLEXERS which I failed to mention. Try looking in the Winter 2005 Ham Radio Outlet catalog. More specifically the products by Comet on page 99 and Diamond on page 103. You'll also notice that the TRIPLEXERS will cover the specific 800 mhz band in question, i.e., Comet model CFX-4310C and Diamond models MX-2000 and MX-3000.

B.T.W., I do know that a DUPLEXER is for a repeater. Thanks for "clearing it up" for me.

 

[grem467]

hahahah nice!

 

[Al42]

No.... THE device I was talking about is a DUPLEXER. There are also TRIPLEXERS which I failed to mention. Try looking in the Winter 2005 Ham Radio Outlet catalog. More specifically the products by Comet on page 99 and Diamond on page 103. You'll also notice that the TRIPLEXERS will cover the specific 800 mhz band in question, i.e., Comet model CFX-4310C and Diamond models MX-2000 and MX-3000.

B.T.W., I do know that a DUPLEXER is for a repeater. Thanks for "clearing it up" for me.

Duplexers normally have the same band on all ports - diplexers normally have a very large frequency spread between ports.

I don't think many people have use for a duplexer with a scanner. Or want to spend the money for one.

 

[kb2vxa]

Hi Al and all,

Oh man, you crack me up, you really put the icing on the cake this time. Are you deliberately trying to mess with thier minds as if they're not confused already? (;->)
"Duplexers normally have the same band on all ports - diplexers normally have a very large frequency spread between ports."
Close enough for government work Al.

"I don't think many people have use for a duplexer with a scanner.
That's what cracked me up.

"Or want to spend the money for one."
Yeah, it's a killer.

Let's get it straight once and for all, IGNORE the sales terms used by ham radio manufacturers and promulgated by salesmen who don't want to argue. Footy, the guys at HRO in New Castle DE at least are hams with heads on thier shoulders, some dope working for an ad agency wrote that catalog.

Duplexer;
A set of extremely narrow cavity filters that allows a repeater to transmit and receive at the same time on the same band in full >duplex< mode with typically 600KHz of frequency separation.
Diplexer;
A device consisting of two L-C filters used to separate or combine two frequency bands.
Triplexer;
Same as above but with three filters for three bands.

From the Collins English Dictionary (pay close attention to the direction of the signals);

duplex (`djul‚ks) n.
permitting the transmission of simultaneous signals in both directions in a radio, telecommunications, or computer channel. Compare diplex, simplex (sense 1).[C19: from Latin: twofold, from duo two + -plex -FOLD]

diplex (`da€pl‚ks) adj.
permitting the transmission or reception of two signals simultaneously in the same direction over a radio or telecommunications channel. Compare duplex (sense 5),simplex (sense 1).[C19: DI-1 + Latin -plex -FOLD, on the model of duplex]

The bottom line is in order to understand the function you must first understand the prefix, it's a language problem if you don't.

"Communications = Education"
Grem, in this case it's mind boggling. (;->)

 

[K5MAR]

Irregardless of the actual, correct term for the item in question (a diplexer), they are labeled and marketed as duplexers by the manufacturers and dealers. So, if I'm trying to direct a technically-unknowing person to the appropriate device for combining two different band antennas into one radio (or the reverse), I'm going to point him or her to AES or HRO and tell them to look for a duplexer, not a diplexer. I know that NCG Comet labels and markets theirs as duplexers, as does MFJ. For those that are bothered by this incorrect use of terminology, I suggest you contact the manufacturers.

Mark S.

 

[Al42]

Irregardless of the actual, correct term for the item in question (a diplexer), they are labeled and marketed as duplexers by the manufacturers and dealers.

Is that something like those dual-band antennas "labeled and marketed" ... "by the manufacturers and dealers" as scanner antennas that receive from 25-1300 MHz?

I know that NCG Comet labels and markets theirs as duplexers, as does MFJ.

I was going to say something about "Might Fine J...", but it might have made the site liable for something not too nice.

 

[SCPD]

Anyway.... now that we all know who can pee the farthest. The particular devices in question, i.e. DUPLEXERS, are the ones I referred to in the catalog(s). I don't care if the terminology is correct or not. If the person seeking help looked for a DIPLEXER in the catalog he/she wouldn't have found what I was referring to. If he/she were looking for a DUPLEXER they would have found the item. It's ony a hobby.

In the scope of things I was merely trying to offer someone some help. I wasn't expecting a barrage of corrections on terminology because some "dealer" or "manufacturer" decided to label their product incorrectly. Instead, I was given a lesson from a dictionary. I don't need to consult a dictionary to know the difference between the two. It's not my mission in life to impress other people. That all ended when I obtained mental maturity. It's only a hobby.

I've been wrong many times in my life and I don't mind being corrected, but there is a right way and a wrong way to do it. I don't care for a smart ass or holier than thou attitude when being corrected. People that I've encountered with this type of attitude usually were picked on in school and beat up alot. They find it easy to hide behind a keyboard and berate people instead of a face to face encounter where they would get their ass whipped like a school girl. If the bad memories of high school ass beatings still creep into your dreams then maybe your therapist could help you. There are lot's of meds out there he/she could prescribe to help with the lack of confidence and insecurity. In the meantime, my offers of assistance on this site will cease. It's only a hobby.

Did I mention that it's only a hobby?