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Old 08-23-2014, 6:13 AM
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Question BCD996xt reception. stationary full signal, driving in car signal goes weak.

I have a BCD996xt. I am monitoring a police agency that is roughly 35 miles from my location. They operate on 155mhz and are digital. I have a 1/4 wave 2 meter antenna, and since I started using it my signal is aweseom, full 5 bars. But here is the catch. If I'm sitting stationary lets say at a red light, stop sign etc. it works just fine. But when Im driving the signal gets weak and the sound is choppy and blocky. Best way to describe it, it sounds like when u are talking to someone on a cell phone and they have weak service. Be advised I am just doing in town driving so im not getting over 45mph. I'm just looking for advice as to why its doing this, and if there is anything I could do to improve it so I can drive and listen rather then have to stop somewhere. Im open to all suggestions. - Thanks
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Old 08-23-2014, 8:24 AM
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Quote:
Originally Posted by mc18 View Post
... If I'm sitting stationary lets say at a red light, stop sign etc. it works just fine. But when Im driving the signal gets weak and the sound is choppy and blocky. ...
When you are sitting still with the engine running, it's OK. If you rev up the engine (still sitting, car in Neutral), does it get bad? If it does, it may be interference from your ignition system - spark plugs.
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Old 08-23-2014, 11:49 AM
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Interesting! I saw this thread earlier before you replied & I was stumped!
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Old 08-23-2014, 12:05 PM
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another thing to look up is multipath interference.
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Old 08-23-2014, 1:05 PM
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Default BCD996xt Reception

This is normal, because the radio signal is line of sight everything between your vehicle and the transmitting site will interfere with the signal. Trees, power lines, hills, and buildings will get in the way. When you are stationary the signal may improve because you have less physical interference between you and the transmitting tower.When you are traveling more objects come in and out of your path and cause more interference with the received signal. Driving in town would be worse because of the amount of power lines, buildings, and other objects in the path.

You may try a higher gain antenna like a 5/8 wave and or a preamp, but understand this may also make your reception worse depending on other radio signals in your area that may cause a different type of interference. Adjusting your antenna to the frequency you are trying to receive may help also, but the distance of 35 miles and being mobile will be tough to overcome. If you are in a small town or rural area the higher gain antenna and preamp may help but will not solve your problem.
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Old 08-23-2014, 1:11 PM
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No it doesn't change if I rev the engine up. But if I'm going over 10mph it breaks up. You think a Larsen 150c 5/8 antenna would help?
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Old 08-23-2014, 1:48 PM
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external antenna is a must for anything other then local. as you move around you hit dead spots and such where the signal is weaker then it is when you sit still plus the signal being weaker still has to go through your car to get to the antenna but with an external antenna you get no interfereence from the metal in your car plus the antenna is higher up and you have more there as far as gain to grab that weaker signal... just my 2 cents lol
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Old 08-23-2014, 1:51 PM
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I currently have a 1/4 wave 2 meter antenna that is directly mounted in the middle of my car that I use.
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Old 08-23-2014, 1:53 PM
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Quote:
Originally Posted by mc18 View Post
No it doesn't change if I rev the engine up. But if I'm going over 10mph it breaks up. You think a Larsen 150c 5/8 antenna would help?
This sounds like a classic antenna connection problem. You have a loose connection at, or inside, your antenna. The wind resistance is moving the loose connection and making it intermittent. You can either find and fix the connection on your existing antenna, or replace the antenna with a different one.
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Old 08-23-2014, 2:09 PM
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ahh ok sorry about that lol i saw you said a 1/4 wave but i didnt see external or top of radio
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Old 08-23-2014, 2:10 PM
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Default BCD996xt Reception

A higher gain antenna will help your reception, but it may also cause intermod problems with your scanner. I used a Hustler 5/8 antenna when monitoring public safety freq in the 155mhz range with good results, but when I came close to pager transmitting sites the scanner became useless because of intermod and I had to turn it off. I turned the scanner back on when I moved far enough away from these sites so after awhile I knew where the interference went away. National Weather frequencies will also cause intermod on certain frequencies.

Inter-modulation distortion happens when signals you don't want to receive mix with the IF frequencies of your scanner and add up to the frequency you are trying to receive. This is received through your scanner as bursts of noise, or distortion that will drown out the communication you are trying to monitor or will open the squelch on your scanner.

A 5/8 wave antenna will give you about 3 dBd gain, your 1/4 wave is probably around 0 dBd. It all depends on your receiving location if you will have trouble with intermod from the increase in gain. If you are traveling in a rural area you may not have any problems, but if your town is large you will most likely have problems with a higher gain antenna. It only hurts the pocket book to experiment.

Do you have any intermod problems now with your set up?
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