[Premium-Rx] Modifying the Ten-Tec RX340

[EDWARD SYLVESTER]

Perhaps Rob Sherwood (sherweng.com) can chime in but he used to offer mods for the JRC NRD-545, as this suffered from the same issue. In this case, he offered a 9KHz or a 6 KHz roofing filter. 

He modified mine and it definitely improved the close in dynamic range, but affected  broadband FM, as this is equipped with a >30 MHz converter. 

.73, 
Ed NI6S

> On 19 Jan 2026, at 2:31 PM, Arthur Delibert via Premium-Rx <premium-rx at mailman.qth.net> wrote:
> 
> I’m sure I’m not the first person to think of this or even to try it, so I’d be interested to hear thoughts and experiences from others.
> The RX-340 is generally a great radio, with one unfortunate exception – it desensitizes in the vicinity of a very strong signal. Also, a weaker signal in the presence of a stronger one will often “pump.” A look at the block diagram shows why this happens.  The only filters ahead of the AGC line are 16kHz wide or more.  So even if you’re using, say, a 2.6 kHz bandwidth to listen to a signal, the AGC is responding to anything within a much broader bandwidth.
> Two of those 16 kHz filters are ceramic. I recently bought some 6 kHz filters (LT455HTW) with the same pin pattern as the originals and installed them in one of my RX340s in place of the 16 kHz filters.  The results seem quite good.  This morning, I was listening to Myanmar on 5985 when a very strong (unlisted and unID) signal suddenly appeared on 5980.  On the unmodified 340, Myanmar was completely crushed.  On the modified one, the LSB was crushed but I could listen with no problem on the USB. (The intruding signal wasn’t modulated, so no “pumping” was observed.)
> That’s the most dramatic example, but there are others – for example, listening to the Ethiopian on 6110 with the NHK flamethrower on 6105.
> There are some drawbacks.  The narrower filter seems to stretch out noise pulses a little more.  Also, I doubt that the filters I found on-line meet the same specs as the ones used by Ten-Tec, and they seem to introduce a couple dBs of attenuation.  The new filters would be a problem if I wanted to listen to a wideband signal, but in 65 years of SW BC DXing, I’ve never felt the need or desire for that.
> I’d be glad to hear other people’s thoughts and/or experiences with this or similar mods.
> Thanks.
> Art Delibert, KB3FJO
> 
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