DXing with car radios

Mark Connelly, WA1ION, USA, 3 August 2004 via NRC-AM

I drove a Pontiac Grand Am on a business trip to Bristol-Johnson City, TN in 1987 or 1988. The front end on that baby was exceptionally sensitive. It sounded as though they were using a varactor circuit that tracked the frequency being tuned and that the Q of the input tank was almost on the verge of putting the front end into regeneration, sort of like a Kiwa Loop but using the car whip. Received bandwidth was tight as a result and sensitivity way up there. The ground conductivity in that hilly area is poor, but still 300+ mile reception of lower band groundwave signals occurred. This thing would have rocked at the seashore or out on the Nebraska plains. I suspect that this may very well be the same Delco model that's in Craig Healy's '88 Blazer.

In the 1970s when I first started seriously Dxpeditioning from the car ('74 Pinto at the time), the first thing I did was place a regenerative FET preamplifier between the car whip and the input to the car radio. At the time I was working at Teradyne in downtown Boston near South Station and my northerly homeward commute along the Central Artery (still the elevated structure in those pre-Big Dig days) was a really slow crawl at 5 p.m., much of the time not moving at all. In autumn and winter I had noticed that I could do a certain amount of DXing with the unaided car radio. Around sunset at the waterfront location, many of the common TA's could be heard. Dakar, Senegal on 764 and Morocco on 818 were two of the "biggies". When I started using the regenerative preselector, I could successfully slice away more usable TA audio on splits that were just hets against domestics on the normal car whip directly to radio set-up. If an opening was a real "screamer", I'd get off the Central Artery and park along Atlantic Avenue near the New England Aquarium, Waterfront Park, and Joseph's Aquarium Restaurant. After about an hour I'd have a good assemblage of DX notes in the logbook and I'd head home. Because traffic was lighter later on, the seaside stop didn't add as much time to the trip as you might think.

When receivers other than the car radio (which, of course, was designed for the high-impedance whip input) were used, use of the preselector became absolutely necessary. In the '80s I did some in-car DXing with the Sony ICF-2001 and ICF-2010 fed by the car whip / regen FET preselector combo. Later on I used a Kenwood R600 before graduating to a Drake R8 (and later an R8A) in the '90s. Though I seldom DX while in motion any more, other than just to spot openings and size up conditions, I have used the Drake R8A and a broadband active whip clamped to the roof rack if I wanted to listen to BBC-5975 or other shortwave on a long ride. I now do most of my serious DXing from the car while parked, usually around local sunset at seashore sites in Rockport and Rowley, MA. Almost always this involves the use of the R8A receiver and two antennas with a phasing unit to create a cardioid pattern nulling to the west.

Most cars are too noisy when running for serious down-in-the-mud MW DX. Your best bet is to use the car whip, the placement of which has been optimized for low noise. It is designed for operating into a high-Q high-impedance tank, so a tuned FET preselector is advised for any receiver other than the car radio itself. Even the car radio can benefit from the use of such a preselector, as noted above. In-window antennas are junk as far as I can tell.

When the car is stopped, noise is usually not a problem (though, in these wonderful modern times, some cars have computerized alarm and other digital supervisory circuits that can generate strange signals even when the ignition is turned off). On the Taurus I have now, about every 30 minutes a low-level buzz noise will come on. You clear it by putting the key in the ignition momentarily if it hadn't been in it, or by removing it momentarily if it had been in. I call the buzz "the voice of da car", not to be confused with something from Senegal. It has been there on two different Taurus models I've had. I have no clue what causes it. It's one of those minor irritations on DXpeditions, like the mosquitoes and gnats at the Rowley salt-marsh.

I think that all automotive receivers should have audio line-in jacks. The need is mostly justified by all the IPods and other MP3 players out there (including audio-loaded laptop PC's). A case for input jacks can also be made by "old-timers" who still want to be able to play cassettes from a Walkman through the car's speakers.
I've tried the FM audio transfer scheme. Many of these devices drift badly and can barely put out enough signal to be consistently clear in urban areas where just about every channel has something on it, either a real station or a mixing spur. Line-in audio is definitely the way to go.