Saturday, September 16, 2006

Eton E1 Preamp, Strong Signal Handling

With a sensitivity at the 0.5uV level, the E1 needs to have a good front-end, especially when connected to large outdoor antennas. According to the block diagram in the user manual, the radio incorporates bandpass filters at 1, 2, 4, 8, 16 and 3o MHz. The preamp (or "DX" setting) is 10dB according to the block diagram. According to specifications, IP3 at 5 kHz spacing, preamp on, isn't really out of this world: -30dBm. It should work well in a "normal" RF environment (can somebody please tell me what a "normal" RF environment is?). What about mine?

My RF environment is surely not normal. It consist mainly of a Loran C transmitter on 100 kHz, 14 km away as the crow flies, and the output is 250kW. I also have an NDB, BV on 399 kHz, 16 km in the same direction. My North American beverages point more or less directly towards them. I have an array of five beverages, at present connected to an antenna selector, via a switchable 10-13dB push-pull Norton preamp, into an amplified 1:8 splitter where the preamp is identical to the first but has a net gain of 5 dB. It is also switchable. Normally I use the splitter preamp all the time, and turn on the other preamp when signal levels drop after sunrise or before sunset. I use the receivers' preamps as I find necessary. But after sunrise, they are indeed needed.

So what's the E1 front-end like? The Loran C should be a good indicator if the receiver is prone to overload. When both external preamps are engaged, there is a bit more Loran C noise below 1 MHz than I find on the other receivers. Nothing dramatic though. However, if I engage the "DX" setting, the Loran C will take over the AGC completely and mute the receiver. But - only below 1 MHz. The front end filters are doing their job. If I disengage one of them (no matter which), the overload disappears.

I also did a test on the 49-meter band at late evening when signal levels are very high. I used an amplified ALA100 8x4m loop, If I engaged all preamps, there was severe intermod. If I disengaged one of them (no matter which) the intermod disappeared.

Mind you that none of the other receivers behaved the way the E1 did.

Conclusion: The Eton E1 is not bullet-proof. Use the internal preamp only when it is really necessary, especially if you have a very strong RF source within the passpand. I feel rather lucky that Eton chose to put the first bandpass filter at 1 MHz and not at 1.8 or 2. That would have limited the E1's capability as a MW DX receiver. However, with the preamp disengaged MW sensitivity will still be close to 1uV. A little disappointment this, but it doesn't really spoil my impression of the E1. I keep comparing it to receivers/transceivers costing at least three times as much and it is doing remarkably well so far.

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