Baffling experience with SpectrumForce wide-band antenna

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designeq

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I’ve run into an issue with my recently-purchased SpectrumForce wide-band antenna (SpectrumForce Wideband Antenna with Mag Mount and BNC | Scanner Master) that has me baffled.

I primarily use two handheld scanners—my GRE PSR-300 and my Whistler TRX-1. The GRE is a much better radio and always outperforms the TRX. The TRX misses the beginnings of some transmissions and misses others altogether. In order to “equalize” their performance, I thought to get the SpectrumForce antenna, with the primary logic being that if I could mount it up high, it would pull in a better signal than the rubber duckies I use on the scanners. This SpectrumForce antenna has generally received good reviews.

I have it mounted on a window ledge at 9 feet. While this isn’t extremely high, it has a much better line of sight than my handhelds. But so far the only real improvement I’ve seen seems to be on the air band.

The thing that has puzzled me is this: I listen to two trunked systems: Clackamas County and Multnomah County (in Oregon).

While the systems in Multnomah County come in ok with the SpectrumForce antenna (but no significant improvement over the ducky) the antenna seems basically deaf to the Clackamas County system. I don’t understand how this can be.

On my handhelds, I use the RS800/Remtronics REM-800 800 MHz duckies. I’ll listen to one scanner with the ducky and the other connected to the SpectrumForce antenna with both scanners scanning the same systems. The one connected to the SpectrumForce picks up almost nothing in the Clackamas County system, but the Multnomah system comes in ok. Then I switch the antennas and I see the same thing in the new configuration—the scanner connected to the SpectrumForce loses the Clackamas County signal and the one with the ducky gets it fine.

So I am completely confused. These are both 800 MHz trunked systems. Why would the SpectrumForce antenna pick up one system and not the other? Both systems come in pretty good with just the duckies.

I can speculate that the SpectrumForce doesn’t really enhance the reception because it is a general wide-band antenna and the signal lost from the thin coax maybe overcomes any gain I would get with the higher mounting. But none of this explains why one trunked system comes in fine while the other doesn’t.

Does anyone have a clue as to what might be causing this or have suggestions that would help me bring in Clackamas County when using the SpectrumForce antenna?
 

designeq

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Portland, OR
Do you have it attached to something metal? If you don't it is not going to work properly.

Hmmm. This is interesting. The antenna has a mag mount so many people use it on their cars. However, I've read that people also use it at home, as I am. I attached a metal plate to the window ledge so that the antenna would stick with the mag mount, but the plate is small. Why do you say it won't work properly unless it is attached to something metal?
 

mule1075

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Hmmm. This is interesting. The antenna has a mag mount so many people use it on their cars. However, I've read that people also use it at home, as I am. I attached a metal plate to the window ledge so that the antenna would stick with the mag mount, but the plate is small. Why do you say it won't work properly unless it is attached to something metal?
Because the metal makes a ground plane. Most of the ppl you see that use it at home have it attached to a cookie sheet,air conditioner etc.
 

designeq

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Thanks for the info. I did some more research and took the following action: 1) I removed the plastic cover from the base of the antenna, 2) I used a piece of aluminum foil (as per the suggestion of mmckenna) that was 36” long by 4” wide, for a surface area of 144 sq. inches. After this I got a small improvement. Clackamas County came in on the GRE (the more sensitive radio) but the Signal Strength meter only registered the S icon. With the ducky, I got 4 bars. I haven’t heard anything on the TRX.

Unfortunately, I don’t have room for a larger ground plane up there. Is the signal strength a linear function of the ground plane size? IOW, would a larger ground plane provide a better signal in proportion to its size?

Also, someone mentioned using sheet metal. Would this produce any significant improvement over aluminum foil? Other than this change, I don’t know what else I can try.

Any other suggestions would be appreciated.
 

N9JIG

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A groundplane works better if it is roughly uniform in size, linear strips may work OK but not as well as a square or circle.

Try mounting the antenna on a large metal object such as a metal shelf, file cabinet or fridge if possible.

Remember that scanner antennas are art as much as science. Since you are not transmitting you can afford to experiment and find different solutions. I have had great luck with these small mag0mounts doing things like hanging them upside down off a ceiling vent, putting them on the outside part of a window mounted AC and using a baking pan as a ground plane until the wife discovered it missing.
 

designeq

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Joined
Aug 20, 2009
Messages
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Location
Portland, OR
A groundplane works better if it is roughly uniform in size, linear strips may work OK but not as well as a square or circle.

Try mounting the antenna on a large metal object such as a metal shelf, file cabinet or fridge if possible.

Remember that scanner antennas are art as much as science. Since you are not transmitting you can afford to experiment and find different solutions. I have had great luck with these small mag0mounts doing things like hanging them upside down off a ceiling vent, putting them on the outside part of a window mounted AC and using a baking pan as a ground plane until the wife discovered it missing.

Hi Rich,

Thanks for the response. I posted my question without realizing the full extent of my being an antenna moron. With the responses of Mule1075 and the detailed private messages from WA0CBW, I’ve realized that this antenna was exactly the wrong one for what I wanted to do. I primarily wanted to get the advantage of height, however, I had no understanding of ground planes (and still am pretty ignorant about them)

Your suggestions are appreciated, however the conditions where I can put this antenna are severely constrained, making it not possible to use a baking pan (no room) or filing cabinet (no height) or other possible solutions. I clearly didn’t think this through, and had not considered the need for a ground plane with the mag mount antenna.

I used a mag mount antenna years ago on my car and since the car itself acted as the ground plane, and the antenna just worked, I was never forced to understand the details of antenna ground planes.

That ignorance showed up in this attempt. Even with the tin foil strip, my reception was worse than with the duckies, in part because the antenna probably became directional (and not in the right direction, if you can believe that!).

So I’ve moved the antenna to its proper position on my car, and I was happy to find that it does work fine in my car.

I appreciate the help people have offered and I have to say that the RR forum rocks in how people are willing to help even those of us suffering from IIS (Impaired Ignorance Syndrome).
 
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