Re: Duo r preamp

Neil Smith G4DBN

I guess that PRE might be Preselector?

The way the DUOr works means you get the same sensitivity across the entire frequency range and with most antennas, you will get enough galactic and manmade noise into the receiver to make a preamp unnecessary.  If it is a special receive antenna, that doesn't apply, but in general, those come with a built-in preamp. Traditional radios probably need a preamp because they are very insensitive as a result of being designed to give a wide dynamic range.  Try the test and see what happens.  If the noise rises by say 5dB with the band open, a preamp will just make things worse by adding intermod products and potentially causing overloads.

Neil G4DBN

On 23/10/2019 16:22, NEIL COLEY via Groups.Io wrote:
Great advice. Thank you. I will make those checks.

I’ve come from the ic7610 radio and I’m used to simply clicking in the preamp on the traditional radios!

I also see “pre” on the lcd screen when powering up the duo r so I assumed pre amp was available

On 23 Oct 2019, at 13:39, Neil Smith G4DBN <neil@...> wrote:

Hi Neil, do you get *any* increase in the noise floor when you connect the antenna(s) for 17 and 10m. If the noise floor rises more than a few dB then a premap isn't going to achieve anything other than reducing dynamic range. If there is no change at all, or less than about 3dB, then it is worth looking at a preamp, although you need to do trhe test when the band is open and there are some signals (unless you are listening to Jupiter radio noise or meteorscatter).

If the noise floor does increase, but you can't hear it in the speaker, try changing the AGC threshold (not sure which menu does that on a DUOr sorry).

Finding a suitable preamp would be tricky, as you would need to ensure it could not be overloaded by out of band signals, so it would need good filtering and use a high-intercept device. Not sure anything like that is avaialble commercially. First step is to ensure that you definitely don't see any increase in noise when you connect an antenna when the band is open.

Neil G4DBN

On 23/10/2019 12:59, NEIL COLEY via Groups.Io wrote:
Preamp for 17 and 10mtr ssb please

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