*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 <[email protected]> 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 < > [email protected]> 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 >> > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
