*Amp/antenna noise *-- is the AD8045 noise low enough for a 3-meter
monopole? *0.26 uV amp noise vs. 0.16 uV man-made rural noise and 2.3 uV
city with a 3-meter monopole. *
Feel free to review my method/math and make corrections as needed.
*Rural Noise*, ITU-R P.372-14 (link below)
Working thru formula (7) on page 4 using Figure 7 the man-made noise (quiet
receiving site) E-field at 1.8 MHz is *4.8 nV/m* in a 1 Hz BW. In a *500 Hz*
bandwidth this is *107 nV/m*. Given that a 3-meter (circle array) monopole
has an effective height of 1.5 meters the antenna terminal voltage is *0.16
uV*. Median city noise is 23 dB higher at *2.3 uV.*
*Noise Calculation Inputs*
6-meter monopole source impedance -j3700 ohms
AD8034 voltage noise 3 nV/Hz^0.5 @ 1.8 MHz
AD8045 current noise 3.2 pA/Hz^0.5 @ 1.8 MHz, thru the 3700 ohm antenna
reactance is 12 nV/Hz^0.5
Total noise voltage is the RSS of 3.0 nV and 11.8 nV = *12 nV/Hz^0.5*
https://www.analog.com/media/en/technical-documentation/data-sheets/AD8045.pdf
https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-14-201908-I!!PDF-E.pdf
Dave KH6AQ
On Thu, Mar 12, 2020 at 6:18 AM Dave Cuthbert <telegrapher9@gmail.com>
wrote:
> *JFET op amp vs bipolar op amps, *LTSpice simulations connected to a 3
> meter monopole
>
> A bipolar op amp doesn't always give the lowest noise with a short
> monopole at 1.8 MHz because the op amp current noise creates noise voltage
> across the antenna capacitive reactance. Additonally, op amps can be
> connected in parallel for lower voltage noise at the expense of higher
> input capacitance (which loads down the antenna signal voltage).
>
> Simulations of the YCCC amp with a bipolar op amp and a JFET op amp were
> performed. Next, preamps having 2, 4 and 6 JFET op amps were modeled. As
> the number of op amps goes up the antenna voltage goes down with optimum
> S/N ratio, in this case, with 4 op amps. It shows 4.5 dB better S/N than
> the bipolar op amp. The bipolar op circuit is modeled with an LTC6228
> rather than an AD8045 because I didn't have to import the AD8045 model into
> LTSpice. I can try to import the AD8045 later if anyone is interested. The
> LTC6228 op amp has 1/3 the voltage noise and the same current noise with
> Bias Current Compensation disabled, so it should show lower noise than the
> AD8045. The JFET op amp is the ADA4637 and IMD simulations were run with it
> looking better than the bipolar.
>
>
> *YCCC amp with bipolar vs JFET op amp for a 3 meter monopole at 1.8 MHz*
> LTC6228 bipolar op amp, 9.5 nV/Hz^0.5, loaded sig 0.93, relative S/N ratio
> 0 dB
> ADA4637 JFET op amp, 6.7 nV/Hz^0.5, loaded sig 0.85, relative S/N ratio
> 2.2 dB
> 2 X JFET op amp, 4.8 nV/Hz^0.5, loaded sig 0.74, relative S/N ratio 3.9
> dB
> 4 X JFET op amp, 3.6 nV/Hz^0.5, loaded sig 0.59, relative S/N ratio *4.5
> dB*
> 6 X JFET op amp, 3.1 nV/Hz^0.5, loaded sig 0.49, relative S/N ratio 4.2 dB
>
> Dave KH6AQ
>
> On Wed, Mar 11, 2020 at 1:49 AM Chris Moulding <
> chrism@crosscountrywireless.net> wrote:
>
>> As well as being a radio amateur (G4HYG) I also run a small business
>> designing and making radio equipment (Cross Country Wireless).
>>
>> Recently I've been asked by a radio contest group to see if I can
>> redesign the YCCC Hi Z amplifier using modern components and using
>> similar mounting arrangements to our Loop Antenna Amplifier.
>>
>> The first prototype using surface mount components is working well.
>>
>> So far I've not build an array of antennas but that will come later when
>> the production boards arrive.
>>
>> The prototype uses a unity voltage gain amplifier and a BNC connector.
>>
>> I've a couple of questions for others on the list with experience of
>> running vertical receive arrays:
>>
>> Is a unity voltage gain amplifier OK or do you think it needs more gain
>> for long coax runs?
>>
>> At present I'm using a BNC male connector for the output. Would an F
>> type connector be more compatible with existing antenna arrays.
>>
>> 73, Chris G4HYG
>>
>> _________________
>> Searchable Archives: http://www.contesting.com/_topband - Topband
>> Reflector
>>
>
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