AMband.org » Reception

Radio-Locator Decoded

Ted — Thu, 19 Jun 2008 14:47:51 +0000

I have received a lot of questions about the contours shown on the Radio-Locator maps. For AM they are:

Red – 3.0 mV/m – Generally the Sellable area of the station
Purple – 0.5 mV/m – Rural protected service area, but nobody would buy ads.
Blue – 0.1 mV/m – You might still get it on a car radio

For FM they are:

Red – 60 db/uV or 1.0 mV/m – Protected service area for Class A and C stations
Purple – 50 db/uv or 0.316 mV/m – A pretty weak Signal, nobody would buy ads.
Blue – 40 db/uv or 0.1 mV/m – You won’t pick it up, except in rural areas

I determined this by comparing the plots of sample stations in Radiosoft’s Comstudy with their Radio-Locator maps. Hopefully this clears a few things up!

NRSC Committee releases AM Quality Study for Reduced Bandwith Transmission

Ted — Mon, 19 Feb 2007 21:04:49 +0000

The National Radio Systems Committee has released a study on the effects of reducing the bandwidth of AM transmissions from the present standard of 10 kHz.Â The study used representative receivers to present transmissions of speech, sports, music and commercials with bandwidths ofÂ 5 kHz, 7 kHz and 10 kHz.Â The study assumes that both the desired and undesired stations operate using the same standard.

The results showed that mutually reducing transmission bandwidth down to 5 kHzÂ is a big plus for speech.Â There was either a benefit, or no change from the 10 kHz results when reducing the transmitted bandwidth to 7 kHz irrespective of format or first adjacent channel interference level.

The study was done with a selection of receivers, and used blind A-B testing to determine listener preference.Â This methodology is superior when the sources are a selection of several transmission bandwidths.

This study assumed symmetry:Â both the desired signal and the undesired signal were limited to the same bandwidth.Â This implies a standard to be adopted by all stations within the AM band, which may or may not be a factor for stations that receive interference from stations in other countries.

Since stations broadcasting speech receive a big plus, there will probably be pressure by the “talkers” to adopt the narrower 5 kHz limitation. Â This is also the bandwidth limitation required for medium wave HD radio’s analog signal.

The study did not include the effect of HD radio interference to first adjacent channel stations, and whether an analog station has any benefit from wider transmission bandwidth when an HD signal is the interferor.Â In the end, HD radio’s medium wave “Digital Only” signal will be an excellent neighbor to other “digital only” and Analog stations, but I expect few stations will be moving to this mode in the next year or so.

Long Distance Radio – The crackling voices of AM from far away

Ted — Thu, 04 Jan 2007 22:43:45 +0000

Late at night, the voice of Sandy Beach at WKBW or Wolfman Jack at XERB would cover the country. You could listen for thousands of miles. It is harder now, but you can still hear radio from across the nation or across the ocean. It takes more skill now that the band is more crowded, but the National Radio Club is ready to help. Check them out!

Receiver Review JVC KD-HDR1 IBOC Car Radio

Ted — Tue, 02 Jan 2007 15:29:32 +0000

I just installed the brand new JVC KD-HDR1 car radio with HD Radio. This is by far the lowest cost HD radio on the market. ($279 after rebate from Crutchfield) It has a lot of features, including multichannel capability, and auxiliary inputs (with adapters) for CD changers, Ipods, XM and Delphi radio.
I give it a 7 out of 10, unfortunately it is the AM section that lowers the rating.

It has a builtin CD/CDR/MP3/WMA player with title text readout too.

Generally it plays pretty well, except the AM band section has a few bugs:
1) It will not scan stations above 1610 kHz! You can step to them and put them in the memories, but you cannot scan to them and have the radio find them.
2) The AM HD radio sensitivity is not so great. I don’t have a good point of reference for the other receivers available, but from my location in Cherry Hill area, WIP and WPEN played fairly well in HD (although both of these stations have serious HD EQ/processing problems), WDAS sounded great, but kept cutting in and out of HD because the signal was not strong enough (1.2 mV/m) to hold the HD in lock. WOR just barely locked up at 0.6 mV/m. The text came in well enough, but the radio rarely went to HD audio andthen only for a few seconds.
3) The AM HD switching is JARRING. When listening to WPEN in analog and then have the digital switch in, it was most annoying. It almost sounded like the station was changed, even though the program was the same. As I mentioned before, the EQ and processing is so different betweeen the HD feed and the analog that it was nasty. There should be a fade in delay of 1 sec or so, not a hard switch. I know that when the signal unlocks there needs to be a hard switch.
4) If you select an HD-2 channel on FM and turn the car off, the radio comes back with the HD-1 channel. Similarly if you set a button for an HD-2 station, it actually gets set for the HD-1 channel.

The FM section played nicely with clean HD signals, and it was fun to sample the HD2 channels.

Audio quality was fine, as far as I could tell on my Jeep stock speakers, unless there is an equalization mismatch between the AM analog and digital signal paths.

Ted Schober