Drive-In-Freak writes:
Here's why so many of us DXers are fond of portables. There's a ton of R.F.I. running through the power lines in this day and age. Again...switchmode power supplies, light dimmers, dirty insulators, computers, and one of the biggest offenders touch lamps (why the F.C.C. hasn't stopped production on these atrocities is beyond me)...just to name a few...send so much garbage down the lines that it can and often does have a very negative impact of AM/MW and SW/HF reception. It's so much of a problem that I'm quite surprised that tabletop radios are still in production and being bought.
Not only is it best to run your radio on batteries instead of plugging it into the wall, it's also a good idea to keep it away from outlets as well as even the wires in the walls and anything that's plugged in. It's always been a bit of an issue but as we have more and more devices that create R.F. pollution the problem has gotten much worse over the past few years and continues to do so. Armstrong thought it was so much of a problem back in the '30s that he invented FM. It's so bad now that I'd have to think that if he was alive today he'd be shocked that anybody bothered with AM anymore.
As far as something running on AC not having enough current to reach it's full potential; Anything that's not complete junk would have a transformer capable of handling the load. If it didn't heat would be a major problem. If you push a transformer too hard it's going to get hot.
A good portable radio is built with battery operation in mind. It will do it's best to be as efficient as possible...efficient speakers and an output amplifier that's slightly below what the batteries are capable of producing (about 1 watt r.m.s. per alkaline D cell) without a lot of current wasted on heat. Yes, it's a compromise, but a good design will squeeze all it can out of what's available.
Again..the only real issue with a car radio set up is the lack of a directional antenna (unless you build a loop of some sort). With a stick antenna nulling isn't possible. Let's say you have a local station on 1430 and you want to tune in another station on 1410 you can't turn the antenna and null out the station on 1430. Also if you have two stations on 1490 you can't separate them. You couldn't null out a source of noise (static) either.
When it comes down to pulling signals in directional nulling can be (and often is) just as important as sensitivity and selectivity. It is a bit part of selectivity.
Add to your list of interference generators: Plasma HDTVs. I just replaced an LED flatscreen with a plasma set, and wow, RF is all over the dail on every AM radio in my house (and that's a lot). Battery-powered sets, too. Might be because it has a switch-mode power supply, not sure. But now I can't watch TV and AM radio at the same time.
Posted by: Ed S. | July 09, 2013 at 09:11 AM
Jay Allen reviews,"C.Crane CC Pocket"
http://radiojayallen.com/c-crane-cc-pocket/
Posted by: Vimal Oberoi | July 09, 2013 at 09:45 AM
Ed: That brings to mind Art Bell's story of buying a new flat screen; he brought a portable radio in to the store and then walked around all the TVs - the one that gave off the least interference was the one he bought. *That's* a dedicated radio guy..
Posted by: StarHalo | July 09, 2013 at 10:25 AM
Something to consider: I also prefer using batteries as opposed to a "walwart" transformer. The only problem is...alkaline batteries will eventually leak. The leaking chemical will adhere to the metal battery contacts & surrounding plastic. As an alternative one can use;
1. Lithium and/or rechargeable batteries.
2. A fully regulated power supply.
3. An external battery tray that plugs into your
radio that use the batteries of your choice.
#3 can use alkaline batteries without the worry
of leakage within the radio.
Posted by: spin | July 09, 2013 at 10:04 PM
I use Duracells and no leakage problems. I exclusively run on batteries; I don't trust some of those internal power supplies on old unobtanium transistors.
Posted by: dorpmuller | July 09, 2013 at 11:49 PM
I have my Kenwood R-2000 receiver, among other RF and audio equipment, using an APC LE1200 for AC power filtering.
http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=LE1200
Up to 55dB of EMI/RFI noise rejection.
I go a step further, as I am using the APC LE1200 to deliver AC to a power strip with a ferrite installed, which seems to further improve noise rejection. You might also want to place a ferrite or two on the APC LE1200 power cord as well.
As with AC power and local noise, YMMV, of course.
Posted by: RobRich | July 10, 2013 at 05:37 AM