Hello
Was just reading through this article here:

http://www.allaboutcircuits.com/vol_3/chpt_4/10.html

and found the link to the Crystal Radio in the second paragraph is broken. Hopefully this can be fixed.

I have also found when I hit one of your pages from Google, the search terms are highlighted. While this is useful for a rare word, when searching for something like 'Bias', it results in the entire document being highlighted all over, making it very difficult to read. Refreshing the page doesn't remove the highlighting.

My solution to this would be a 'Hide highlighting' button at the top the article when this feature is activated. This way the benefit is still there, but can be hidden when it becomes intrusive. I hope you can take this feedback into consideration - keep up the great work

 

In addition, there is a typo in 'Kirchhoff's' name a bit further down the article

 

Hello,

You are right about the link.
I think that the link should go to this page:
http://www.allaboutcircuits.com/vol_3/chpt_9/6.html#03442.png

Bertus

 

I have also found when I hit one of your pages from Google, the search terms are highlighted. While this is useful for a rare word, when searching for something like 'Bias', it results in the entire document being highlighted all over, making it very difficult to read. Refreshing the page doesn't remove the highlighting.

This is googles doing, nothing to do with this site. It normally does it when you view the google cashed version of the site, but not the actual site.

 

I'm pretty sure it is not Google doing it. I was using Chrome, but have just re-tested and it still happens in Internet Explorer (no Google Toolbar installed). I am looking at the actual page, not a cached copy (as determined from the address bar).

For example - if you search for 'transistor biasing' in Google, a couple of results down there is an allaboutcircuits entry. Clicking this link takes you to the highlighted version in both Internet Explorer and Chrome. As far as I know Google have no influence over this, so I assume the page is extracting the keywords and highlighting them automatically.

 

Bertus - yep, that looks like the correct place for it to link to

 

Try accessing them without using a search (not bookmarked). I've never seen the effect you're talking about.

 

Just to clarify for those who have not seen the effect - I am aware I can open a 'private browsing' window to mask the search terms, or bookmark it and go back to the page. The suggestion was to help the casual users reading a page found via a search engine - some pages become very difficult to read with the highlighting applied.

Specifically, the javascript that does this highlighting is located here on the allaboutcircuits website:

http://www.allaboutcircuits.com/scripts/se_hilite.js

Briefly looking over this code, it applies highlighting for all searched terms from Google, Yahoo, Ask, etc. I assume a button could be added to the pages to disable this feature on demand.

Hope this makes it clearer!

 

Again, it is an artifact how you accessed the site, not the site itself. It is basically coming from your end, so there is very little that can be done here.

 

Here is how I see this site, going through the internal links (and only showing part of the article)...

Although transistor switching circuits operate without bias, it is unusual for analog circuits to operate without bias. One of the few examples is “TR One, one transistor radio” TR One, Ch 9 with an amplified AM (amplitude modulation) detector. Note the lack of a bias resistor at the base in that circuit. In this section we look at a few basic bias circuits which can set a selected emitter current IE. Given a desired emitter current IE, what values of bias resistors are required, RB, RE, etc?
Base Bias

The simplest biasing applies a base-bias resistor between the base and a base battery VBB. It is convenient to use the existing VCC supply instead of a new bias supply. An example of an audio amplifier stage using base-biasing is “Crystal radio with one transistor . . . ” crystal radio, Ch 9 . Note the resistor from the base to the battery terminal. A similar circuit is shown in Figure below.
Write a KVL (Krichhoff's voltage law) equation about the loop containing the battery, RB, and the VBE diode drop on the transistor in Figure below. Note that we use VBB for the base supply, even though it is actually VCC. If β is large we can make the approximation that IC =IE. For silicon transistors VBE≅0.7V.

Base-bias
Silicon small signal transistors typically have a β in the range of 100-300. Assuming that we have a β=100 transistor, what value of base-bias resistor is required to yield an emitter current of 1mA?
Solving the IE base-bias equation for RB and substituting β, VBB, VBE, and IE yields 930kΩ. The closest standard value is 910kΩ.

What is the the emitter current with a 910kΩ resistor? What is the emitter current if we randomly get a β=300 transistor?

The emitter current is little changed in using the standard value 910kΩ resistor. However, with a change in β from 100 to 300, the emitter current has tripled. This is not acceptable in a power amplifier if we expect the collector voltage to swing from near VCC to near ground. However, for low level signals from micro-volts to a about a volt, the bias point can be centered for a β of square root of (100·300)=173. The bias point will still drift by a considerable amount . However, low level signals will not be clipped.
Base-bias by its self is not suitable for high emitter currents, as used in power amplifiers. The base-biased emitter current is not temperature stable. Thermal run away is the result of high emitter current causing a temperature increase which causes an increase in emitter current, which further increases temperature.
Collector-feedback bias

Variations in bias due to temperature and beta may be reduced by moving the VBB end of the base-bias resistor to the collector as in Figure below. If the emitter current were to increase, the voltage drop across RC increases, decreasing VC, decreasing IB fed back to the base. This, in turn, decreases the emitter current, correcting the original increase.
Write a KVL equation about the loop containing the battery, RC , RB , and the VBE drop. Substitute IC≅IE and IB≅IE/β. Solving for IE yields the IE CFB-bias equation. Solving for IB yields the IB CFB-bias equation.

Collector-feedback bias.
Find the required collector feedback bias resistor for an emitter current of 1 mA, a 4.7K collector load resistor, and a transistor with β=100 . Find the collector voltage VC. It should be approximately midway between VCC and ground.

The closest standard value to the 460k collector feedback bias resistor is 470k. Find the emitter current IE with the 470 K resistor. Recalculate the emitter current for a transistor with β=100 and β=300.

We see that as beta changes from 100 to 300, the emitter current increases from 0.989mA to 1.48mA. This is an improvement over the previous base-bias circuit which had an increase from 1.02mA to 3.07mA. Collector feedback bias is twice as stable as base-bias with respect to beta variation.

 

I agree it will look normal going through the internal links. What I am referring to is the highlighting of keywords that have been searched for in a search engine. To see this effect you need to do the following:

1) go to www.google.com
2) search for: transistor biasing
3) find the allaboutcircuits link in the results - around 5 or 6 down from the top
4) click the link, and note how all the mentions of the words 'transistor' and 'biasing' are highlighted (in green and blue)

It is this highlighting I am talking about - wholly controlled by the allaboutcircuits website through a javascript include. It is reading the 'referrer keywords' sent by google to the next clicked page (standard with webpages), and it is then highlighting them one-by-one. This is not a browser feature, is not Google's doing, but is a hard-coded feature of the allaboutcircuits website. I am hoping it can become optional, because the highlighting is intrusive when pages are found using a search engine in this way.

I hope this is clearer.

 

Oh, it was clear to begin with. As we keep saying, this is an artifact that has nothing to do with this site. It is entirely caused by other software, which we have no control over. There is nothing this site can do to fix the problem.

You are mistaken about where the problem is. My suspicion is your browser has ad ware, a mild form of malware.

To remove them, once you've found the page, access it directly. If it still does it then your browser is infected.

 

Hi Bill
I'm willing to accept if I am mistaken, and am just trying to help improve the site for new visitors. To humour me, what happens when you click this link? :

http://www.allaboutcircuits.com/scripts/se_hilite.js

This 'se_hilite' script in long-hand stands to Search Engine Highlight. If you can see this file, and it offers to download (or shows the contents), then the highlighting *is* being done by the allaboutcircuits website - specifically, by this javascript file.

 

Hello,

I think the highlighting is indeed done by the forum using the search words from google.
I dislike google so I always use altavista as a search engine.

Bertus

 

Thanks Bertus - glad I'm not going mad!

Interestingly, if you look at the script itself, it is set up to do highlighting for AltaVista searches too, but it is so old that AltaVista have changed their site and it no longer works correctly. They used to use 'aqa=' as their search query string (which is what the script looks for), but they now use 'q=' instead.

Which I think is all the more reason to remove this outdated script from the allaboutcircuits site! Or maybe allow it to be disabled with a simple button