Radio Freq Antennas

Improving reception of medium wave broadcast stations. The reception of medium wave broadcast stations has become worse for several reasons. The receivers that are sold nowadays still have the possibility to tune to the medium wave band. The quality of the AM-part of most receivers is not better than that of the cheapest portable radio. With modern techniques this could be much better. With a communications receiver the reception is much better. However, the filters in most modern communication receivers are too small for high fidelity reception. While the performance of the receivers is decreasing, the interference levels increase as a result of the use of digital circuits, switched mode power supplies, energy saving lamps, digital motor control etcetera. In some areas the interference levels are so high that the reception of medium wave broadcast stations is almost impossible. But to solve your problem, what can you do? Most man made noise is distributed mainly by the mains wiring. Even at a short distance of a building the reception is much better. Using an outdoor antenna will help. Coupling the antenna signal via isolated RF transformers prevent common mode ground signals to enter the receiver. Ferrite rod antennas can be connected to a coaxial cable, using an extra winding of one or two turns. Big antennas are not necessary, the signal strength is high. Unfortunately the noise level is also high. A receiver made before 1970 or an old car radio is sometimes much better than a modern receiver. You could decide to build your own radio or improve an existing radio. High sensitivity is not important. Narrow bandwidth and high dynamic range are. The use of a synchronous detector in stead of a simple diode detector will reduce the unwanted signal output. Signals in the upper sideband and signals in the lower sideband that are not related to the carrier are reduced this way. In some radio receivers the coupling capacitors are too big. The result is that small clicking noise pulses with high amplitude are rectified in the RF and IF amplifiers and temporary change the bias voltages setting of those amplifier stages after each pulse.  This way the small pulses are widened and distortion will occur. Replacing those capacitors by capacitors with a lower value might help. Resulting noise pulses can be clipped or cut out using a noise limiter or noise blanker circuit. As you can see there is a lot to improve. I hope this information will help you to improve the reception of your favourite radio station.

jvdberg, your post is greatly appreciated and your knowledge is impressive.  I have been interested in all things electronic all my life, but my background and profession are completely apart from that.  consequently, your post is a bit over my level of understanding.

so please, if you will, allow a specific question or two that stem from your post:

[my receiver is a rel new, expensive do everything box with HDMI switching for my TV etc & I'd like 2 see what I can do with RF AM signal interfearance on that device w/o rewiring anything inside that box]

- do I remove the ferrite bar, connect a coax running 2 a better location and put the ferrite bar on the distant end of the coax?  and, what did u mean by an extra turn (of wire) or two to do the connection?

- i am purchasing an in-home elect power line noise filter for use on a branch circuit that has hard-wired smoke detectors that talk to each other & a few more plug-in noise filters to go on the power cord ends of several suspect appliances for my home (by suspect, i mean likely a source of line surges since they have motors-compressors;  these from www.X10.com (items XPF-TEL and XPPF-CS-122205-TEL).  do you think this would help my AM RF reception?

thanks 4 your interest & expert commentary.

jvdberg, your post is greatly appreciated and your knowledge is impressive.  I

have been interested in all things electronic all my life, but my background and

profession are completely apart from that.  consequently, your post is a bit

over my level of understanding.

so please, if you will, allow a specific question or two that stem from your

post:

[my receiver is a rel new, expensive do everything box with HDMI switching for

my TV etc & I'd like 2 see what I can do with RF AM signal interfearance on that

device w/o rewiring anything inside that box]

- do I remove the ferrite bar, connect a coax running 2 a better location and

put the ferrite bar on the distant end of the coax?  and, what did u mean by an

extra turn (of wire) or two to do the connection?

- i am purchasing an in-home elect power line noise filter for use on a branch

circuit that has hard-wired smoke detectors that talk to each other & a few more

plug-in noise filters to go on the power cord ends of several suspect appliances

for my home (by suspect, i mean likely a source of line surges since they have

motors-compressors;  these from www.X10.com(items XPF-TEL and

XPPF-CS-122205-TEL).  do you think this would help my AM RF reception?  Or, what

about a choke (on the coax to the relocated ferrite ant, or on the pwr cord of

the receiver?

thanks 4 your interest & expert commentary.

It is possible to modify a radio with a ferrite antenna into a radio with a connection for an external antenna. To do this, you have to remove the ferrite rod and replace it by an inductor with the same inductance. I did this using a small ferrite ring core. After the removal of the ferrite rod I measured the inductance of the coil and the tap. I wound the ferrite ring core to achieve the same inductance. I did this so well that it was not necessary to realign the radio. The photograph below shows how this was done. On top of this photograph the ferrite antenna that is no longer in use. The red wire is the coupling winding to the coaxial cable.