Portable radio AM dxing

iMONITOR

Member
Premium Subscriber
Joined
Sep 20, 2006
Messages
8,665
Capacitor - 365pF, Variable, Single Section
1610496668913.png
 

Patch42

Member
Premium Subscriber
Joined
Feb 14, 2008
Messages
266
Even though the two stations are on the same frequency the likelihood of them also coming from the same direction is very unlikely. I discovered this technique while out in the country far away from any electrical interference. It does work in an urban/sub-urban environment albeit with less satisfying results.
The trick, which seems counter-intuitive, is to rotate the radio/antenna not to maximize the signal you want but to null/minimize the signal you don't want. Most radios can boost a signal more than enough to get decent reception on a weak signal, but they can't do anything about eliminating a signal that gets through the antenna. Rotate the radio until the interfering signal disappears and then try peaking the remaining signal. The CCrane EP-Pro and CCR2E/3 have very sharp nulls that can do a lot to minimize even a fairly strong local signal.

The all-time best, if you can find one, is the CCrane TCF Twin Coil Ferrite amplified antenna.
Probably the best option of what's currently being produced, but not the all-time best. The Kiwa air-core loop and the Quantum QX Pro both have capabilities the TCF doesn't have. Sadly, neither is still in production. If you love MW DXing and you ever see one of either for sale, grab it. Be prepared to dig very deep in your wallet. I've not seen one in ages, not that I've been looking, but the last Kiwa I saw for sale went for something like $500.

I stumbled into a closeout sale on the TCF at Fry's a long time ago. They were selling them for $29. I bought all they had on the shelf. Sold them over time to dedicated DXers at a small profit for me and a huge discount for them.
 

majoco

Member
Joined
Dec 25, 2008
Messages
3,697
Location
New Zealand
Just be very careful connecting a long piece of wire to the whip antenna - often the whip has a high gain FET amplifier right at the base - these FETs are very static sensitive - the voltage generated by you walking across a carpet and then touching whip is sometimes sufficient to blow the FET. Outdoors the same static voltage can be generated just by the wind blowing across a bare wire! Better to connect the external wire to a socket marked with the antenna symbol or make one of Mike's attenuator boxes.
 

WA8ZTZ

Member
Joined
Feb 23, 2014
Messages
776
Just to summarize some of the things maybe already mentioned...
Many portables have no provision for directly connecting an external antenna to the radio for AM band reception.
The whip antenna is for FM/SW use, it does little or nothing for AM reception. AM reception relies on the radio
internal ferrite loopstick. Generally, radios with longer internal loopsticks are better performers.

So, you have to come up with some method of inductively coupling an AM signal to the radio. This can be accomplished
by positioning something like the AN-200 near the radio and use inductive coupling. You will have to move the AN-200
around a bit to find the sweet spot for maximum signal transfer. You will be amazed at how much it will improve reception.
There is a jack on the AN-200 that allows the included cable to be connected directly to the radio if the radio has terminals
for an external AM antenna.

The directional capability of the loop comes in very handy for peaking desired stations and nulling unwanted stations...
a great feature for use on the crowded AM band. Stations broadside to the loop will be nulled while stations in line
with the axis of the loop will be peaked. Put the loop and the radio together on a lazy susan for a convenient easily
rotatable platform. Be aware that when using the radio alone without an external loop and relying only on the radio
internal loopstick that the peak signal will be broadside to the loopstick while the nulls will be off the ends, which is
somewhat opposite of the external loop.
 
Last edited:

Patch42

Member
Premium Subscriber
Joined
Feb 14, 2008
Messages
266
You will be amazed at how much it will improve reception.
The only caveat I'd mention is that radios with large, good quality ferrite antennas will probably not be improved a great deal by a small air core loop. If you want to build a 3-foot diameter loop, that's a different story, but an AN-200 is unlikely to make a big improvement with a CCRadio 2E, EP-Pro, RF-2200, or GE Superadio. With anything smaller it will usually make a huge difference.

Put the loop and the radio together on a lazy susan for a convenient easily
rotatable platform.
Altering the orientation of the external loop and the radio can sometimes make a difference in difficult reception situations. For instance, when trying to null one of the local flamethrowers, I often find it necessary to first null the local as best I can with the radio alone and then bring the external antenna back into play, also nulling the local with that antenna. Without doing it this way the local can sneak through and overpower the desired signal. You can also sometimes overlap the nulls of the internal and external antennas in a way that reduces the depth but increases the breadth, allowing you to reduce multiple signals enough to receive a desired signal. You just have to play with the orientations and see what happens.
 

BDavis27707

Member
Joined
Jan 3, 2021
Messages
16
Location
Durham, NC
I have downloaded the FCC data for broadcast bands for my location. Part of the dataset is the Azimuth of the station from my location. That gives me a good starting orientation for my loop. I've been using NS6T's Azimuthal Map to get my bearings.
 

Boombox

Member
Joined
Sep 2, 2012
Messages
921
Even a small loop will improve performance of a Superadio or PR-D5 or similar higher performance portable. Even a dB or two can make the difference in IDing or catching a weak station. And then there are DXers who live in low signals areas (areas of the US, and the world, that have lower ground conductivity) and a loop will definitely help there also.
 

krokus

Member
Premium Subscriber
Joined
Jun 9, 2006
Messages
4,657
Location
Southeastern Michigan
Capacitor - 365pF, Variable, Single Section
Thanks for that link. I have been looking around for one of those, and that site has stuff I can use for some antique radios I want to restore.
 

Boombox

Member
Joined
Sep 2, 2012
Messages
921
I have downloaded the FCC data for broadcast bands for my location. Part of the dataset is the Azimuth of the station from my location. That gives me a good starting orientation for my loop. I've been using NS6T's Azimuthal Map to get my bearings.
A caveat: the compass bearing to the station from your location, and the real world bearing may be completely different animals. Local magnetic anomalies, and the vagaries of skywave propagation can be tricky. Some of the California stations here (and California is directly south of my state) come in up to 30-40 degrees away from where they should, due to local hills, and possibly a local magnetic anomaly.
 

WB9YBM

Active Member
Joined
May 6, 2019
Messages
847
Location
Niles, IL
A caveat: the compass bearing to the station from your location, and the real world bearing may be completely different animals. Local magnetic anomalies, and the vagaries of skywave propagation can be tricky. Some of the California stations here (and California is directly south of my state) come in up to 30-40 degrees away from where they should, due to local hills, and possibly a local magnetic anomaly.
There's also a difference between "true north" and "magnetic north"; Wikipedia probably explains that better than I can, so here's an excerpt:
Magnetic north and magnetic declination

Magnetic declination from true north in 2000.
Main article: Magnetic declination
Historically, the magnetic compass was an important tool for navigation. While it has been widely replaced by Global Positioning Systems, many airplanes and ships still carry them, as do casual boaters and hikers.[27]

The direction in which a compass needle points is known as magnetic north. In general, this is not exactly the direction of the North Magnetic Pole (or of any other consistent location). Instead, the compass aligns itself to the local geomagnetic field, which varies in a complex manner over Earth's surface, as well as over time. The local angular difference between magnetic north and true north is called the magnetic declination. Most map coordinate systems are based on true north, and magnetic declination is often shown on map legends so that the direction of true north can be determined from north as indicated by a compass.

In North America the line of zero declination (the agonic line) runs from the North Magnetic Pole down through Lake Superior and southward into the Gulf of Mexico (see figure). Along this line, true north is the same as magnetic north. West of the agonic line a compass will give a reading that is east of true north and by convention the magnetic declination is positive. Conversely, east of the agonic line a compass will point west of true north and the declination is negative.

North Geomagnetic Pole
Main article: Geomagnetic pole
As a first-order approximation, Earth's magnetic field can be modeled as a simple dipole (like a bar magnet), tilted about 10° with respect to Earth's rotation axis (which defines the Geographic North and Geographic South Poles) and centered at Earth's center. The North and South Geomagnetic Poles are the antipodal points where the axis of this theoretical dipole intersects Earth's surface. If Earth's magnetic field were a perfect dipole then the field lines would be vertical at the Geomagnetic Poles, and they would coincide with the Magnetic Poles. However, the approximation is imperfect, and so the Magnetic and Geomagnetic Poles lie some distance apart.

Like the North Magnetic Pole, the North Geomagnetic Pole attracts the north pole of a bar magnet and so is in a physical sense actually a magnetic south pole. It is the center of the region of the magnetosphere in which the Aurora Borealis can be seen. As of 2015 it was located at approximately 80°22′12″N 72°37′12″W, over Ellesmere Island, Canada but it is now drifting away from North America and toward Siberia.

Geomagnetic reversal
Main article: Geomagnetic reversal
Over the life of Earth, the orientation of Earth's magnetic field has reversed many times, with magnetic north becoming magnetic south and vice versa – an event known as a geomagnetic reversal. Evidence of geomagnetic reversals can be seen at mid-ocean ridges where tectonic plates move apart and the seabed is filled in with magma. As the magma seeps out of the mantle, cools, and solidifies into igneous rock, it is imprinted with a record of the direction of the magnetic field at the time that the magma cooled.
 

Patch42

Member
Premium Subscriber
Joined
Feb 14, 2008
Messages
266
There's also a difference between "true north" and "magnetic north"
It doesn't help that the magnetic north pole keeps moving and this movement is accelerating. If you need accuracy you need to be sure you're using up to date conversion factors between magnetic and true north.

I recall a number of years ago the magnetic/true difference became an issue when a group of listeners were trying to determine the location of a mystery open carrier using reports of signal direction from all over the U.S. Unfortunately the effort proved fruitless as the techniques for direction finding using conventional equipment is far more involved than most appreciate and getting an accurate direction on an open carrier is almost impossible on a radio without selectable SSB.
 

PACNWDude

Member
Joined
Oct 15, 2012
Messages
834
+1 on the Tecsun PL-360, or the PL-365 which adds SSB. The PL-365 is also sold as the CountyComm GP-5/SSB and sold to many government agencies for use overseas and in emergency kits. Having SW receive can be handy at times. Lots of great information in this thread.
 
Top