[AMRadio] FM transmitter

Jim Candela jcandela at prodigy.net
Sun Mar 5 09:16:16 EST 2006


    Mack in the early 1970's I did something similar
to your six meter signal blanking the guys FM radio. I
was a novice, wn8pep, and was experimenting with old
computer circuit boards (RTL logic). The transistors
were silicon 2N706, and would often oscillate when
testing in my transistor tester using the long leaded
aligator clip option for in circuit testing. If I
wiggled or twisted the leads, the FM radio, or TV
would be disturbed. 

    The oscillator discovery lead me into a series of
oscillators placed inside of tin cans with a variable
knob. Eventually I AM modulated the things (AM = ALL
modulation!). Once I blanked my mothers FM stereo, and
then I modulated my own program material. I was
blanking "elevator music" and replacing it with "hard
rock" rebroadcast from an am radio. My mom went
through fits about this!

    A few years later when WB8PEP, and in a college
dorm, I evolved this transmitter into a MOPA design
with the oscillator collector modulated. Since the PA
was class C, the final emission was mostly FM with a
little AM. For about 3 months in the winter-spring of
1975, Puterbaugh hall had a Saturday night broadcast
that was campus wide. This was WRFP, radio free
Puterbaugh. With a groundplane coat hanger antenna on
top of a 3 story building, and maybe 50mw of power, we
achieved full campus coverage with good quieting, and
decent quality. We had pre-recorded announcements, and
used the dorm main desk for requests. It was a lot of

Jim Candela

--- SBJohnston at aol.com wrote:

> > So sometimes others find our contacts interesting.
> True - when I was a teenager in Ohio I ran a lot of
> 6m AM.  I didn't know it 
> but my 2E26-based 3 watt signal was getting into the
> local cable-TV system and 
> being amplified and carried all around the
> neighborhood - or perhaps even all 
> over that part of town.  I learned about it when an
> elderly neighbor stopped 
> me walking home from school and said that she'd
> heard me on her TV and found 
> my discussion of the new designs for "space
> shuttles" interesting.  She also 
> said that she'd talked to other people she knew and
> they were hearing me too.  
> They all knew who I was but none of them ever
> complained.
> That also points out how old the space shuttle
> design has become... 
> I did have another neighbor complain very harshly
> about my 6m AM operations 
> one time...  He was hearing me on his stereo when he
> played records on the 
> turntable.  I  tried to explain how it might be
> happening and how we could fix it 
> - but he just said if it happened again he would
> "kill me".   Yeah right... 
> real nice to threaten a 13 year old.
> A few weeks later I was looking out my bedroom
> window and noticed this bozo 
> working on a new stereo for his "rockin' van".  He
> was listening to an FM 
> station on 100.7 MHz as he hooked up the speakers in
> the rear doors..   I got the 
> bright idea to key up my six meter rig on 50.4 and
> the sure enough the second 
> harmonic blanked out his reception beautifully. 
> Each time he went back to work 
> on one of the speakers I keyed up and his outfit
> went silent.  Then when he 
> jumped up and ran to the front to fiddle with the
> radio I unkeyed and his FM 
> reception returned.  I made him dance back and forth
> for a considerable time...  
> I still cherish the memory.
> Steve WD8DAS
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