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I have a Tecsun PL-660 (link is to the manual) has the usual AM/FM radio telescoping internal antenna, and a 1/8th-inch jack for an external shortwave antenna. There appears to be no facility for attaching to station ground, unless one of the terminals in the 1/8th inch jack can be attached to a station ground. It has USB/LSB single-sideband modes, as well as AM reception and pretty good general coverage from about 3200 khz up, in AM and SSB, plus commercial AM/FM and air-band coverage.

My question is: It stands to reason I should get better reception on the 80 meter, 40 meter, 30meter, 20meter ham bands if I build a proper dipole for each, and manually switch them out. With better quality non-portable amateur radio receivers and transceivers there appears to be a way to ground the radio. Perhaps one of the pins on portable radios is also possibly the station ground pin? Does anybody ground their portable radios when using them for Shortwave listening?

I have lost the little bit of wire attached to a headphone jack as shown in the picture here, that makes up the provided shortwave listening antenna:

enter image description here

I'm about to experiment and see if I can't get good reception with a home-made replacement, or rather set of replacements, but as dipoles instead of just random-wire.

What I think I know is that:

  1. That for a particular shortwave band, a dipole for that frequency will be resonant and will thus be ideal for receiving that band.

  2. A coaxial feed, with the jacket of the coaxial feed attached to station ground will be good.

  3. That it won't take long to figure out which terminal (pin) in the 1/8th-inch 3-pin connector is for the actual antenna.

Things I don't know:

a. What the impedance of the radio tuner is.

b. What else can be done if I want to improve overall reception quality.

c. I intend to just experiment with wiring up the dipole to the two pins on the headphone jack but I have no idea if the little portable radio is likely to even have both pins connected inside the radio.

Has anyone ever made their own antennas for little portable AA battery receivers like the Tecsuns (or Grundigs or other similar units)?

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  • $\begingroup$ You should probably be able to get away with installing an external antenna somewhere with lighting. $\endgroup$
    – user9468
    Commented Feb 4, 2018 at 10:40
  • $\begingroup$ The Tecsun manual has some hilarious word choices. I believe since lightning and lighting are both valid english words, it simply escaped the Tecsun manual author's notice that he/she used the wrong word. Pretty funny. I myself hope never to experience Thunder and Lighting at the same time, either. :-) $\endgroup$
    – Warren VE3WPX
    Commented Feb 4, 2018 at 17:48

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Receiving is all about signal to noise ratio. If most of the noise is generated outside of the receiver (as it is on most HF bands) then matching the antenna system to the receiver increases the signal and the noise by the same amount so you have no change in the signal to noise ratio. Thats why the mismatched random wire works so well on HF receivers and impedance match is not so important in that case.

VHF/UHF is a different story because the majority of the noise is usually generated by the internal receiver circuits. In that case matching the antenna system to the receiver input impedance does make a difference because it increases the signal without causing a corresponding increase in noise so the signal to noise ratio improves and you copy better.

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  • $\begingroup$ SO stick with random wire for receivers on HF. Cool. $\endgroup$
    – Warren VE3WPX
    Commented Feb 4, 2016 at 2:23
  • $\begingroup$ I use a beverage antenna for my RX and a dipole or doublet for TX. Some good info on it here: w0btu.com/Beverage_antennas.html $\endgroup$
    – Bobby
    Commented Feb 4, 2016 at 7:02
  • $\begingroup$ But not too much of an antenna. While getting more signal to the receiver is generally good, if you're living close to a transmitter, especially one that's being overdriven, you'll find that signal overloading the front-end on your radio. (People in this situation will want to make/buy a broadcast-band filter, such as one of these, here.) $\endgroup$
    – Andrew Beals
    Commented Jul 5, 2016 at 15:47
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Tecsun PL660 antenna is connected to the gate of the J-FET for frequency range 1700 kHz to 30 MHz. This is a high impedance. The measured graph can't be correct. The measurement signal voltage must be low enough to prevent switching diodes to go in conductive state.

The FET transistors in the diagram have non-consistent gate-drain-source connections. The diode D3 without dc-current is also a simplification in the schematic. The signal for frequency range 100 kHz to 1710 kHz comes from the ferroceptor. The gate from the FET is connected to the (about) 1 mH ferroceptor inductance, and the drain is connected to a feedback-current winding and to diode D0. The noise matching is not affected by this feedback. The conversion from field strength to output signal can be made frequency-independent with this feedback. For frequency range 1710 kHz to 30 MHz the signal path is via D1 to the low-pass filter just before the first balanced mixer with the two J-FETs.

When you want to see a real and correct diagram, different from the PL660, that makes use of similar techniques look into Philips (Magnavox) D2935 schematic diagram: more complex but also a lot more sensitive. In 1980 I did the design of this "portable" receiver, which was planned to be better than the finally produced Philips radio :)
PA0FSB Brightnoise

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    $\begingroup$ Hello, and welcome to this site! $\endgroup$
    – Mike Waters
    Commented Apr 25, 2020 at 22:34
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Find out the input impedance by connecting different versions of unun impedance transformers, 1:1, 1:2, 4:1, 9:1, and seeing how the signal is improving or degrading.

High impedance 500-10000 ohms. Medium impedance 200-500 ohms. Low impedance 25-150 ohms.

For a given length of wire, as frequency goes up the impedance generally goes down. A quarter-wavelength wire antenna will have an impedance of 35 to 75 ohms, but that length of wire on other frequencies will be high impedance.

I think if the radio feeds the antenna input to the gate of a FET transistor frontend, it will have a millon-ohm input impedance. Just try a balun feeding to whip antenna and the negative battery terminal, with alligator jumper wires connected to the high impedance side of the balun.

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Ground terminal is on the 3.5mm antenna jack for PL600. PL660 may use similar circuit. Both units look very similar on the outside.

I experimented with 3 inch wire loop antenna and did successful QRP DF (direction finding) at 14MHz. The telescopic antenna has poor directivity. Once the loop antenna was plugged in, the telescopic antenna was disconnected and now it has good directivity, so, the ground pin was definitely there.

I believe a longer wire, up to 50 meters or even longer, at higher level and away from strong noise source like fluorescence lamp, will improve reception. You may try connect and disconnect the ground terminal at the ant jack to see what changes. PL600

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According to this:
https://sites.google.com/site/g0ftdradio/tecsun-pl660

enter image description here

It's about 35 Ohm.

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