Way OT : Any java experts here ?

I hate it when I can't figure something out, but this has me stumped...

This online Helical Antenna Design Calculator has an error in it - it gives an incorrect answer for the wire length required.

I looked at the page source, and saw that the calculations are done with a javascript, I found the error quite easily. I decided to use the java formulae in an excel spreadsheet so I could get correct results.

After doing the excel equivalent of the java calculations, I spotted that my excel sheet gives a different answer for the antenna Gain than the answer given by the javascript.

The javascript formula is ...

G= 10.8 + 10*log( CL*CL*N*SL )/LN10;

Given that C = lambda, and CL = C/lambda, CL is always going to be 1.

N is the number of turns (10), and SL is an input value, typically 0.25

So the javascript returns 14.8 dB gain

My excel formula for G is ...

=10.8 + 10*LOG(CL * CL * N * SL)/LN(10)

... which gives 12.5 dB gain

CL is 1.00000
N is 10
and SL is 0.25

The two formulas look to be equivalent to me, but they give different answers, and I can't figure out why... It's been driving me crazy for a few days. Can anyone shed any light on it ?? I'm starting to think that the java isn't handling the LN10 division correctly, but I've got nothing to test it with.

I have attached the full javascript from the web-page, and my excel file...

Log called like that in Javascript is not Log10, It is LogE.

The javascript would need to specifiy the formula as such to work like Excel.

G= 10.8 + 10*log10( CL*CL*N*SL )/LN10;

You are dividing by LN(10), but Excel defaults to base 10 log and Javascript (so I'm told) defaults to base e... could that be the issue?

Did you break down the steps of the calculation to understand where it comes from??

https://exceljet.net/excel-functions/excel-log-function

https://www.w3schools.com/jsref/jsref_log.asp

The Math.log10() function returns the base 10 logarithm of a number

The Math.LN10 property represents the natural logarithm of 10


The natural logarithm of a number is its logarithm to the base of the mathematical constant e

I am unable to break down the steps of the calculation, I have nothing to run the javascript on...

daba said:

The Math.log10() function returns the base 10 logarithm of a number


The natural logarithm of a number is its logarithm to the base of the mathematical constant e

I am unable to break down the steps of the calculation, I have nothing to run the javascript on...

Click to expand...

Go here http://math.chapman.edu/~jipsen/js/

Paste in G= 10.8 + 10*log( 2.5 )/LN10;
Run.
Then paste G= 10.8 + 10*log10( CL*CL*N*SL )/LN10;
Run that.

Ahhhh !!! Got it

The Math.log() function returns the natural logarithm (base e) of a number

Corrected my spreadsheet formula to...

=10.8 + 10*LN(CL * CL * N * SL)/LN(10)

and all is well... Thanks all

Thanks for the heads-up on that online javascript tool... !