radio modifications?

[concrete_hed]

I have a question for those electic engineers out there. Is it possible to modify a normal anolog AM/FM radio to tune into around 10 - 27 mhz or higher? I think most short wave radio's these days use SSB (single side band) and i know you need special circuits to recieve them. I dont want to get too technical but I have a theory that by modifying the variable capacitor or the coil, i can pick up other frequencies. can someone please tell me if im an idiot for thinking this?

 

also, are most cb radio's/walkie talkies FM or AM?

[YT2095]

CB in the UK is largely FM, in the USA it`s AM.

but yes you can convert an FM radio Down to 27MHz, and you can convert an AM upwards through the lower part of the Shortwave band, you`ll be unlikely to get the thing working up to 27MHz though, the IF stages won`t stretch so good.

the only "Problem" you`re going to encounter is bandwidth, CB chans are a 10Kc spacing, FM radios are much wider, so you`ll be listening to a few CB chans at once.

[bascule]

I have a question for those electic engineers out there. Is it possible to modify a normal anolog AM/FM radio to tune into around 10 - 27 mhz or higher?

 

Depends on what type of tuned circuit it's using and what your idea of "modify" actually means.

 

I think most short wave radio's these days use SSB (single side band) and i know you need special circuits to recieve them. I dont want to get too technical but I have a theory that by modifying the variable capacitor or the coil, i can pick up other frequencies. can someone please tell me if im an idiot for thinking this?

 

The variable capacitor and coil form a tuned circuit. Modifying them without knowing what you're doing will most likely prevent you from receiving anything. Modifying them while knowing what you're doing will allow you to receive other frequencies within some hard limits regarding the hardware you're using, so again, the answer is: it depends.

 

also, are most cb radio's/walkie talkies FM or AM?

 

AM

[concrete_hed]

ok, so im thinking i could just wind my own coil to use in the radio. Does an AM/FM radio have 2 different coils (one for AM and one for FM) because im sure they would be completly different. What about the antenna, would it have to be extended? raised high above the ground? because cb's dont put out anywhere near as much power as a proper AM station.

[YT2095]

they have 2 seperate coils, the AM one is a ferrite loop-stick antenna, the FM one is a small coil (usualy local to the vari-cap) with about 4 windings.

often set in Wax also.

This is the coil that you need to modify!

think, 108 / 4 =27 so that`ll give you a rough idea of what you need to do to the coil

rem, the larger the coil, the lower the freq.

you CAN also fine tune if you use a ferrite grub screw inside this coil

 

oh yeah, and to make absolutely sure you have the right coil, tune into a station, and then insert a small jewelers scredrived into the middle of this coil (carefull not to alter or damage it) IF it`s the correct one, you`ll lose your station (it`ll appear again much higherup on the dial) until you remove the screwdriver

[DV8 2XL]

Probably the simplest thing to do is build a converter that will tune the frequencies of interest and output a signal somewhere in the radios normal band. These used to be very popular in the old days, and many hams used to use such devices to get started in the hobby.

 

Check out the kit:

 

http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=SC1C

[YT2095]

funny you should mention that, I was just discussing something in IRC this morning about using a converter with an offset making a beat frequency with the receiver and the hetrodyne would resolve to audio without ever having to take the back off the radio at all, a simple local oscillator will have pretty much the same effect

even so, the IF stage and bandwidth would still let in more than one chan at a time, you Could take the 6 filter out and put a 10.7 or 10.695 (even better) in though

[DV8 2XL]

On the otherhand it kind of begs the question of why you would want to go this route, when reasonably selectve/sensitive recivers that cover up to +30Mhz and have AM/SSB/FM detector-discriminators can be had for cheap.

[YT2095]

and the Fun in that resides Where?

[DV8 2XL]

Ya, well if that's the object, and you crave the magic perfume of flux and solder the best answer is to build a receiver from scratch.

 

Try here:

 

http://www.web-ee.com/Schematics/Simple%20Superhet/simple_het.htm

[YT2095]

hehehe the 414 and 386, I`ve not seen those in ages damn good ICs too!

the TDA7000 would have been my choice though as it`ll do 1.5 to 150mhz nominaly, I use a TBA820M for the audio.

but that`s FM use only (although it will do a pretty good job of AM to be listenable).

I`ve had alot of fun in the past with the 414 though, I think I still have one in my semis drawer, I may just dig it out