Improving ufh voice radio
Improving ufh voice radio
(OP)
I am using a motorola cdm750 voice radio in a carbon fiber race car. The frequency range is 450 Mhz to 470 Mhz and I am currently using a 3db gain antenna and the power is up to 25 watts on the radio. My problem is that as soon as I lose line of sight the radio is nothing but static pretty much. The odd thing is that I am using a data telemtery radio in a 440 Mhz range and I do not lose the transmission when I lose line of sight. Any suggestions to improve this situation? Also would it be helpful to clear up any static if I used a noise filter on the inline power?
RE: Improving ufh voice radio
Q2- Where is the antenna located on the car?
Q3- What model of antenna do you have?
Q4- Do you have a ground plane under the antenna mount?
It is likely that you have a mobile antenna that requires a ground plane. These are relatively easy to install. If this is a roof or trunk mounted antenna, you can install a self adhesive aluminum ground plane under the surface of the ceiling/trunk, then ensure there is good electrical contact to the antenna housing.
You can also try a no ground plane antenna; Antenex has a 3dB gain, low profile stealth design antenna that requires a Motorola style mount, P/N- ETRA4503.
I would install a filter on the power to the radio, every little bit helps.
RE: Improving ufh voice radio
Here is a link to the current antenna that I am using. It is a bulkhead mount style. The car is a LMP2 Race Car, all carbon fiber body.
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The telemetry radio antenna is located on the right side of the car where the voice radio antenna is located in the center of the car in front of the driver.
RE: Improving ufh voice radio
RE: Improving ufh voice radio
You DO need a ground plane to get it working properly.
Refer to thread http://www
RE: Improving ufh voice radio
RE: Improving ufh voice radio
Has anyone checked the current antenna system? Measured the VSWR? ...not for purposes of tweaking to perfection, but simply to confirm if things are connected properly at all.
RE: Improving ufh voice radio
RE: Improving ufh voice radio
Any additional ideas?
RE: Improving ufh voice radio
Huh? Checking VSWR means inserting the appropriate meter into the coaxial cable (using a coax jumper, preferably down near the radio) and simply taking the reading. What exactly do you mean by "depending on the area.." ??
Also, starting the car shouldn't affect it. If it does, then the connections are loose.
By the way, 1.3:1 is perfectly acceptable if that is an accurate reading.
Might as well check the transmitted power while the meter is connected. Usually just turn the slug around or flick a switch. What type of VSWR meter was used?
A high electrical noise level in the car would not normally be expected to affect the outgoing 25 watt transmitted signal other than any noise you might hear on the transmitted audio (when the car is within radio range). In other words, having someone whisper in your ear doesn't normally affect your ability to shout.
On the other hand, a high noise level in the car might certainly make the radio deaf, even if the noise is rejected by the FM discriminator (in other words, the radio can be deafened by a high noise level even if you don't hear much noise on the driver's headset). But, most normal electronics doesn't generate much noise at frequencies as high as 470 MHz.
RE: Improving ufh voice radio
I think, the voice 3 inch antenna energy is getting sucked up by your composite fiber, which also makes the VSWR look good. It's like adding a resistor to your antenna. The Telemetry radio looks like it's attached to a metal oval shape. The voice antenna can't be 3 dB gain, a bit o marketing going on there, maybe 3 dB directivity, but probably -3 or -5 dBi gain.
To evaluate if the carbon is sucking up the energy, try taking Reynolds wrap aluminum foil, circular shape, 15 inch diameter and add it to the base of the voice antenna, oriented horizontally. Alternatively, take 4 wires (each 10 to 20 inches long, awg #24 or thicker) with alligator clips and attach them to the voice antenna base, spread them out horizontally. Or just strip them and wrap them around the antenna base and tape them down. If your range goes up alot, it's probably the carbon fibre as the culprit.
Can you also see what your signal strength is when your receive Voice. Have someone with a spectrum analyzer compare the voice and telemetry signal strengths. If the antenna is the culprit, you'll see big differences just standing in front of your vehicle.
kch
RE: Improving ufh voice radio
A battery nearby is unlikely to be any issue other than shielding, nor will a real bad VSWR prevent transmission over a mile or so with a 25W TX, provided some sort of antenna is connected. The proximity of the ECU might affect reception due to EMI.
What is the problem again, is it transmission from the car to base, or received signals at the car? A source of local interference could block reception, and an antenna that is radiating straight up in the air could block things both ways.