Radio reception hints from the engineer

Dave Barnett's picture

I'm often asked by people "how do I get a better signal on KVMR".  Unfortunately, there's not always an easy answer to this question.  There are two factors that affect reception:  signal strength and interference.  If a desired signal is very strong then reception is almost never a problem.  If the desired signal is weak you can usually make it stronger with a good antenna.  But FM signals in the Sierras are almost never "very strong".  This is due to the terrain we live in.  So there is almost always some interference.  The most common sources are:

1.  Electrical noise - computers, LED lights, compact fluorescent lights, TV sets, cable decoder boxes, and light dimmers are common sources of electrical noise.  Whether your particular device is a problem is hard to say.  But an easy way to tell is to take a portable radio outside, away from everything electrical and tune in KVMR.  Then take that same radio inside and see if your reception deteriorates.  If it does, move the radio around the house and see where reception is good and bad.  You will generally find the offending device.  To check if that is the culprit, temporarily unplug it and see if the reception clears up.  Based on your findings you may be able to locate the radio in a different place for better reception.  If you listen on a home stereo system you may be able to locate the antenna for that system either outside or near a window.  More on that later.

2.  Interference from other FM stations - KVMR has a somewhat unique situation in that we are on 89.5 in the foothills and there is a strong station in Sacramento on 89.3.  This would normally not be a significant problem, as today's modern radios can effectively select between these two frequencies.  What makes reception difficult in some areas is something called "HD Radio".  This is a new method of broadcast that utilizes nearby frequencies on either side of a station's main channel.  The 89.3 FM in Sacramento transmits a digital signal on 89.1 and 89.5 FM.  This would not normally be a problem, however in KVMR's case the situation is unique.  Again because of the mountainous terrain of the region.  The digital signal from Sacramento can cause significant interference in KVMR's coverage area because many places are line-of-sight to the 89.3 transmitter North of Sacramento.  As with electrical noise, the noise from HD Radio interference can also be mitigated by proper antenna placement.

ANTENNAS:  More than anything else, the FM antenna - whatever it is - plays an important part in getting clear reception.  Whether it be the telescopic antenna on a boom box, the little t-shaped antenna that comes with your stereo, or a rooftop FM yagi.  The antenna can be used to increase the desired signal as well as minimize interferernce.  For now we're going to concentrate on two common types - the line cord antenna and the dipole.

1.  Line cord antenna - Do you have a radio that doesn't seem to have an antenna at all?  It plugs into the wall and that's it?  Clock radios & table radios typically fall into this category.  Well, guess what - the power cord is your antenna.  Try moving the power cord around and stretching it out.  Maybe connect it to a different outlet with an extension cord.  In general you want the desired signal to be broadside to the power cord and interference can be minimized by orienting the cord so that the interference source is off the end of the cord.  You may be amazed at how reception improves just by moving the cord a few inches.

2.  Dipole antenna - This is the t-shaped antenna that often comes with an FM receiver or tuner.  I often find them hooked up but stuffed behind the receiver.  Don't do that!!  The top section of the "T" is actually a sensitive antenna.  As with the line cord, you should move this around to find best reception.  Typically these work well taped to a window that is facing the KVMR transmitter site.  As with the line cord, best reception is typically found with the station broadside to the wire and the interference off the end of the wire. 

TRANSMITTER SITES:  KVMR currently uses four transmitters for our signal.

89.5 - the main tranmitter on Banner Mountain (interference to this signal comes from Elverta Road to the North of Sacramento)

88.3 - the Camino transmitter in the Apple Hill district above Placerville

105.1 - Mt. pluto, the highest slope in the North Star ski area

104.7 - In the hills west of Esparto

I'm always interested in reception reports from our listeners - good or bad.  Please send them to engineer@kvmr.org.