QRM from TV Receivers on 136kHz

Known Problem Sets

Users of the 136kHz band are increasingly troubled by noise and carriers from neighbouring television receivers.  Although modern receivers are designed and tested to comply with the requirements of EN55013, the European Union EMC Specification, the only tests performed below 30MHz are conducted emission tests (ie from the mains cable) and not for radiated emissions.  The radiated levels of some current models, both in the lf and the hf bands, leaves something to be desired.

An excellent article on hf emission problems from televisions appeared in the EMC column of RadCom (The RSGB member's magazine), August 2000 pp80-81.  In that article Dave Lauder G0SNO of the RSGB EMC committee gives an outline of the problems and a whole list of TVs which have been reported to radiate noise on the HF bands - most of the noise in this case tends to peak around 18MHz.

However this page is devoted to reporting problems in the 136kHz band (and 73kHz).

Interference problems on 136kHz come in various forms.  Most TVs use switched mode power supplies operating at around 50-75kHz.  The harmonics of these can be heard in the 136kHz band as carriers, often drifting in frequency and modulated with a buzz whose pitch varies with the video content being transmitted.  More of a problem are instability problems in the television which produces a wide rasping noise over a fairly wide band of frequencies.  It has been reported that digital tv set top boxes and cable tv systems can also produce this sort of interference.

It is hoped over time to build up a picture of the extent of this problem, and to that end I have offered to build a database of televisions with their known problems, which ones to avoid and which ones seem OK.  Please send any information, preferably for UK sets only,

I have the following information at the moment:

Grundig MW82 Arganto series   No problems (G3YXM)

Panasonic TX25CK1    Strong rough carrier spreading up and down several hundred Hz (GW4HXO)
Panasonic TX28DK1    No problems (GW4HXO)
(Could be that the strong carrier is just sufficiently out of band though)

Toshiba 32Z17B  Intermittent rasping noise s9+ spreading over many kHz.  Strong rough carrier on 140.5kHz) (G3YMC)

Information published here is for information only.  I have had no direct involvement with the sets mentioned, and I cannot vouch for the accuracy of the information.  No specific recommendations are being made of any one make of TV over another, and I am not responsible for any problems resulting from use of the information.
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