Pre-amp suitable for connecting to 70 watt HF amp?


I believe I read that the output impedance of the LimeSDR is too high to go directly to an HF amplifier. If that’s the case, what kind of HF pre-amp would folks recommend?

I’m planning on assembling one of those $20 eBay HF amps, and it would be nice to be able to use it with the LimeSDR.


The impedance should be the standard 50 ohms.


The impedance should be the standard 50 ohms.

That makes sense. Does the LimeSDR have enough output power to drive an HF amp directly?


Obviously not, the amp should have an input for external power.


I intended to ask does it have enough signal power for a typical HF amp’s input. I’m not an EE or radio expert, so I’m probably using the wrong terminology. Apologies for that.


No problem, I’m not either. The power output of the LimeSDR should be enough to be used in a normal amplifier.


Thanks. I also just saw this thread, where I’ll ask about my specific HF amp.


I may have not been clear but I assume your LimeSDR has the HF mod.


The thread you saw is a good one. Those are good inexpensive products to get what you want done. The Lime puts out 10mW max. Every 10dB is x10, so an amplifier that puts out 20dBm is 100mW, 30dBm is 1W, etc. Gain is adding dB. So if you have a 10dBm output like the Lime and you have a 30db amplifier you get 40 dBm, or 10W. This is of course limited by the maximum power of the amplifier. Another useful relation is every 3dB is a doubling. 6dB is x4. You can feed one amplifier into another to keep stepping it up as long as you are not going over the input spec or driving higher than the output can go.

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@dylanmc - Dylan,

And check this posting I did awhile back, too ------> LimeSDR as a Amateur Radio Transciever

That’s the amplifier I’m going to use with my LimeSDR and the only thing you’d need is a 10dB pad because the amplifier drives at 0dBm, but outputs 45W (+46.53 dBm).

Let us know if you need anything else…

73 de Marty, KN0CK