RFI

[kwired]

When I was a younger man I had a cb for running up and down I-95 along the US east coast. I had a fuzz buster mounted right on top of it on the dash. In probably 30+ trips I got pulled over once (cop in the median turned on radar only after he saw me) and I paid $50 cash and no points/ record. Not sure where the $50 went and didn't care.

You may have been happy because nothing went on your driving record, but that cop was likely in the process of building up his non employer contributed 401k:happyyes:

 

[K8MHZ]

When I was a younger man I had a cb for running up and down I-95 along the US east coast. I had a fuzz buster mounted right on top of it on the dash. In probably 30+ trips I got pulled over once (cop in the median turned on radar only after he saw me) and I paid $50 cash and no points/ record. Not sure where the $50 went and didn't care.

I've known some radio operators but just don't have time to commit to the hobby. Enlighten me though, other than civil emergency, what are some constructive uses for two way radio?

Now that we have tv, cell phones, texting, antisocial networking, etc. is amateur radio waning? A cell phone really is a two way radio.

The answer to that question would be enough to start several threads on.

AKAIK, there are now more licensed amateur radio operators now than there ever has been. Around 700,000 in the US or so.

One could have asked, a hundred years or so ago, if the invention the motorized boat would be the end of sailing. Of course, it wasn't.

 

[mike_kilroy]

Any radio receiver front end is made up of many frequencies, this is called super heterodyne, the cheaper the front end the more IF frequencies, or it may not be coming into the radio through the antenna at all,....

Hurk, you said this in reply to another thread recently too. Since you said it again, I thought I should correct you so you understand what superhyt rcvr means....

I may not get all the words perfect, but after a lifetime as an electrical engineer, of Extra class ham radio and 1rst class commercial licensing (when it still meant something) I think I can explain it some...

In the old days of radio the receiver was simply a cat's whisker into a rock of selenium, or similar material, and it rectified the "input." This input was 'tuned' by having an LC in front of it. As a kid, I, like many others of the Flash Gordon era, used an old oatmeal container to wrap our coil around. We tuned by moving the cats whisker on the rock.....

Then Mr. Armstrong invented the 'regenerative' receiver, then the heterodyne then the super heterodyne receiver. You can google those intermediate ones, but the superhet simply added an oscillator to mix a given SINGLE frequency with the incoming signal or frequency and get a sum and subtraction one. One was thrown away via filters; the other was then used to contnue amplifying the incoming signal. Typically this was an intermediate frequency (IF) of 455kc. By doing this, the selectivity could be increased by magnatudes.

If the input freq is high enough (like fM radio band, then a SECOND IF is used first - typically 10.7Mhz. It is not often that a 3rd IF is used, even today. So you see there is no relation between the 'the cheaper the front end the more IF frequencies" and reality. Actually the more expensive the receiver, the more IF channels.

The superheterodyne receiver has nothing like 'lots of multiple frequencies" on the input compared to any other receiver. Virtually every receiver today is a superhet design - even the single chip receivers.

 

[GoldDigger]

What you can say is that the combination of a single local oscillator frequency (per tuning setting) with the non linear circuit that does the mixing can cause output at the IF frequency for strong enough RF signals which are on the "wrong" side of the local oscillator frequency or are separated by subharmonics of the IF frequency, as well as from two strong signals whose difference is the IF frequency independent of the local oscillator frequency.
One result of this can be the appearance of a sensitivity to multiple frequencies if you do not have a sufficiently selective RF stage or stages before the mixer.

Tapatalk!

 

[kwired]

The answer to that question would be enough to start several threads on.

AKAIK, there are now more licensed amateur radio operators now than there ever has been. Around 700,000 in the US or so.

One could have asked, a hundred years or so ago, if the invention the motorized boat would be the end of sailing. Of course, it wasn't.

But you likely will not find any commercial watercraft that are powered by sails, pretty much just recreational watercraft. Imagine an aircraft carrier or other huge vessel that is powered by sails

 

[GoldDigger]

There are designs for cargo vessels that use wind power though. If fuel costs go high enough, the tradeoff of travel time for fuel economy becomes important.
Not pure sail power of course, since some other motive power has to be present for backup and maneuvering.