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Author Topic: Pre-amp gain on the IC7300  (Read 379 times)

VK3LU

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Pre-amp gain on the IC7300
« on: February 02, 2021, 01:42:06 AM »

Does anyone know what the gain of pre-amps 1 and 2 are on the IC7300?
Both manuals have no info.

Nev
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K6SDW

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Re: Pre-amp gain on the IC7300
« Reply #1 on: February 02, 2021, 03:32:19 AM »

Here's an in-depth technical article that goes into great detail regarding the ICOM IC-7300 system. It includes the Preamp numbers. https://www.ab4oj.com/icom/ic7300/7300notes.pdf

Also the August 2016 QST review of the IC-7300 has performance numbers as well.  Hope this helps.

GL       
« Last Edit: February 02, 2021, 03:46:08 AM by K6SDW »
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W6RZ

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Re: Pre-amp gain on the IC7300
« Reply #2 on: February 02, 2021, 07:49:10 AM »

Looking at the AB4OJ report, there's some conflicting data.

On page 8, he says 7 dB for preamp 1.

On page 11, in table 3, the overload point changes by 13 dB with preamp 1 and an additional 4 dB with preamp 2.

On page 15, in table 12a, the S-meter changes by 7 dB with preamp 1 and an additional 4 dB with preamp 2.

One thing that is known is that there's a 20 dB gain ADC driver in front of the ADC (an LTC6401-20).
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K0UA

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Re: Pre-amp gain on the IC7300
« Reply #3 on: February 02, 2021, 08:39:12 AM »

One thing to remember is to NEVER use either preamp below 30 Mhz. Unless maybe your antenna is the size of a fountain pen. Always be thinking how much to reduce the RF gain on this rig, not adding preamp. 

Reduce the RF gain until the S meter just barely kick up from the zero point during static crashes. Now you have found the noise floor of your system. Operate from there.
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73  James K0UA

K6AER

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Re: Pre-amp gain on the IC7300
« Reply #4 on: February 02, 2021, 09:43:35 AM »

How much does the noise floor rise on the spectral display/ That is your preamp gain.

I use the preamp sometimes on 10 meters and on 6 meters.
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VK3LU

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Re: Pre-amp gain on the IC7300
« Reply #5 on: February 02, 2021, 08:02:54 PM »

Thank you everyone. I downloaded the PDF and will read it when time allows.
I wanted the gain figures as I am thinking about setting up a mag loop just outside the shack and if the preamp would give enough lift to the sigs. Failing that, I would need to instal a preamp at the loop.

Thanks again.
Nev
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N2DTS

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Re: Pre-amp gain on the IC7300
« Reply #6 on: February 03, 2021, 05:47:34 AM »

I tried that, it works well.
The bigger the loop the better up to a point.
I tried a number of setups with and without a preamp at the loop, various preamps and baluns with mixed results.
The thing with loop antenna's at my QTH is I really need a rotator, as they are directional, and I never bought one.

I also transmitted into a few preamps at the loop doing comparisons and switching back and forth between multi antenna's.
It just takes a second to forget which antenna you have selected....

In my case, I had most of the local noise come from one direction and could null that out very well, but you really need to be able to turn a loop as conditions change and for different bands.
The bigger loops worked better on the lower bands, I tried making a larger one out of copper tubing which worked well 80 meters and up but did not hold up as it was just an experiment.

I used quad shielded cable from CATV hookups and made balun's to test.

I think if you only had a vertical antenna, a loop would be a great RX antenna to kill the noise.
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VK3LU

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Re: Pre-amp gain on the IC7300
« Reply #7 on: February 03, 2021, 11:14:45 PM »

Thanks Brett,
A vertical for tx and a loop for rx is what I am aiming at so it looks like the preamps might work. A bit of fun ahead!

Nev
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N2DTS

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Re: Pre-amp gain on the IC7300
« Reply #8 on: February 04, 2021, 06:08:23 AM »

I bought the MFJ loop, which worked quite well, and seemed to have a very good preamp in it.
I quickly fried that one and bought a few off ebay that worked quite well.
I also got another version that uses coax which is good for portable work as it comes apart.
I made the one out of copper tubing with a plastic electrical box with the amp or the balun in it, it worked well and was better on 80 meters.

The MFJ was quite good as it has a fat conduit for the loop, broad banded and sturdy.
They really DO call for a rotator though, even if just to peak signals.
The null (off the sides) is deep.
I never tried it horizontal....
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