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Ok now I am in deep doo doo

U

undecidedcallsign

New Member
Nov 3, 2013
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So all know my on going issue with reception with my puny little radio and magnet mount antenna. I tried to upgrade today to a slightly larger antenna. Its a Maxrad 2700. Its 52" from base to tip. It has small solid stem and coiled spring. Whip starts out pretty thick and tapers as it goes up. I took it of its standard NMO mount and tried a trunk lip mount part number BMC-NC and...... oh and now I see the problem. It says mini 800mhz trunk mount. I guess that's why my Swrs are off the scale. Is there anyway to convert this lip mount?

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Last edited:

undecidedcallsign said:
So all know my on going issue with reception with my puny little radio and magnet mount antenna. I tried to upgrade today to a slightly larger antenna. Its a Maxrad 2700. Its 52" from base to tip. It has small solid stem and coiled spring. Whip starts out pretty thick and tapers as it goes up. I took it of its standard NMO mount and tried a trunk lip mount part number BMC-NC and...... oh and now I see the problem. It says mini 800mhz trunk mount. I guess that's why my Swrs are off the scale. Is there anyway to convert this lip mount?

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Click to expand...

The mount doesn't have anything to do with the resonant frequency of the antenna. If the antenna screws, properly, onto the mount it should work. I can't see your install or know your skill levels, so I can only give some suggestions to check. I don't want to insult your intelligence, so forgive me if I make suggestions that you already are aware of.

The antenna's advertised bandwidth is from 25 to 31 MHz. I don't know what your desired frequency of operation is, but unless you are using 25 MHz, trimming of the radiator will probably be required.

You may need to scrape a little paint for a good contact point on the under side of the trunk for a good connection. Or install a short ground strap. Unlike the magnet base antennas, which use capacitive grounding (meaning not direct contact), the trunk lip mount will need a good contact with the vehicle body. You can scrape a little paint where small set screw(s), that locks the mount onto the trunk lip, contacts with the trunk. You will want to dap a little hot glue, caulking, pro-flex, etc. to seal the exposed metal to prevent corrosion.
 
Don't be afraid to insult me. Other then being a soldier and leo and am pretty stupid in electronics and such. I put the old mount back on thatbis supposed be screwed on to the body. Its a 90 angle with 3 holes in it. I tried grounding straigh to the battery. Good news and bad. The good: swr meter isnt pegging anymore. The bad: still reading 3.5 through the whole xb band 1-40

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Ok I took the antenna apart. The guy listed this as a cb antenna and even said he pulled it off a truck and the radio it supposedly worked with was a uniden pro520xl. Well the antenna insides says Mlb4700. Not 2700

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This is the antenna style I want. Should I buy the trunk lid mount that I linked above or will this mini 800mhz work? I realize I will need to get a mlb2700 now that I see it is a mlb4700.

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Here is a pic of the inside. Does this look original?

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The MLB-4700 antenna is designed for 47-54 MHz (covers the Amateur 50-54 MHz, 6 meter band). The base coil is too small for the 27 MHz band, and the whip antenna is also to short (very short) to allow operation in the 27 MHz band. You need to get a MLB-2700 whip or a Larsen NMO-27 (B or C) whip antenna. BTW: The BMC-NC NMO mount will work for any NMO mount antenna from 0 to 960 MHz.

73,
Mike
 
Thank you. Your the man. While I got you, As if I don't have enough troubles can I hook a cb and scanner to the same antenna? I have a bear tracker (Bear Tracker BCT2) that scans up 900mhz. I see many troopers around here that have a zillion antennas. Up to 2 maxrad long whips, up to 3 maxrad small stubbies and one super long one mounted on thw back rear driver side quarter panel that comes out at a 90 degree and has a spring coil base. I imagine that is a cb antenna. Back to the mlb4700 for a second. Being that's a 50-54 mhZ that is why my swrs were off the scale? It was like keying up without an antenna at all?

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I would get the MLB2700 as that is what is meant for the frequency range you need. Remember that it covers down to 25 MHz so it will be long for 27 MHz. You will probably have to trim some of the whip. Grind some paint where the set screws of the trunk lip hit the trunk. That is probably the reason why the permanent mount is giving you a lower reading on the meter than the lip mount. It has a good connection while the trunk lip doesn't.


I would run one antenna per device. Aside from the chance of accidentally forgetting to change the radio switch from the scanner to the radio and keying up, you have to think of the resonance of antenna. Resonance affects performance on incoming signal as well as outgoing. Most public safety use frequencies above 150 MHz. That may not matter for you, as I don't know the range you are needing. But I would just get an antenna designed for that frequency range. I use a 2M mobile as a scanner in my truck and it picked up signal much better with a 1/4 wave (19") 2M antenna than it did when I had it connected my 102" CB antenna. And I mean a lot better.
 
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roadrage said:
I would get the MLB2700 as that is what is meant for the frequency range you need. Remember that it covers down to 25 MHz so it will be long for 27 MHz. You will probably have to trim some of the whip. Grind some paint where the set screws of the trunk lip hit the trunk. That is probably the reason why the permanent mount is giving you a lower reading on the meter than the lip mount. It has a good connection while the trunk lip doesn't.


I would run one antenna per device. Aside from the chance of accidentally forgetting to change the radio switch from the scanner to the radio and keying up, you have to think of the resonance of antenna. Resonance affects performance on incoming signal as well as outgoing. Most public safety use frequencies above 150 MHz. That may not matter for you, as I don't know the range you are needing. But I would just get an antenna designed for that frequency range. I use a 2M mobile as a scanner in my truck and it picked up signal much better with a 1/4 wave (19") 2M antenna than it did when I had it connected my 102" CB antenna. And I mean a lot better.
Click to expand...

i agree with this. one antenna for each band . also trunk mounts are tricky at best . and with some knowledge and liil luck you can get a usable swr. my best was usually around 1.5-1.8. i think having the antenna below the roofline has alot to do with it.also if
your swr is high on the entire band ya wanna use then thats a sign of bad ground
another problem with trunk mounts.now for grounding going from your antenna all
way to the battery is way too long of a run for ground. all grounds should be kepyt
as short as possible its been said to keep them 9feet or less for 27mhz . personally
id keep it around a foot or less. id try ground the mount uning a bolt to a bolt on the trunk
lid. scratch off a lil pint on bolt on trunk lid . this may work idk for sure. but this should be
a much better ground being it a much shorter
 
Ok a braided grounded strap in my trunk. I will run a grounding strap/wire from the screw bracket to the braided line. If I run this grounded strap I still need to grind the paint off where the screws contact the trunk? What type of wire would you use? The wire will only be 2 foot or so. Lastly they have a Maxrad scanner antenna Bmaxscan-1000, unity gain 1/4 wave, 21" high and covers 150-174, 450-470, 800-840. This would be good for the scanner?

By the way guys ur all the best. Very helpful for a true dummy. You ever need some shooting lessons look me up

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Use the MLB-2700 for the CB and the Bmaxscan-1000 for the scanner. That's the best thing to do.

Regarding the trunk mount: You should get by with just the mount; making sure the set screws dig through the paint and grip the metal of the trunk lid. That works most of the time. Stubborn cases require ground straps (that's two), one on each side of the trunk lid to the car body. Just make sure the ground strap is long enough to allow the trunk lid to open all the way (usually 2 ft or so). Ground straps are typically made of 1/2" or 3/4" copper or tinned copper braid. This is like the ground straps used to ground an engine to the chassis available a most automotive supply stores. You can also get them at DX Engineering or Amateur Electronic Supply (AES), although the price may be higher.

Regarding the MLB-4700: That antenna is designed for 47 to 54 MHz, and like you have seen, the SWR is off the scale because it isn't resonant anywhere near 27 MHz.

73,
Mike
 

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