I have a vintage Knight Wireless Broadcaster, as I mentioned in an earlier post. It has been the subject of fairly extensive modifications, entirely in the audio department to date. I use it with an isolation transformer so that I can directly ground the chassis to earth ground. 🙂 It will deliver 100V p-p of RF directly to a 10′ wire antenna without any attempt at matching.
Where it falls down in comparison to today’s LPAM equipment is in the use of an unstabilized carrier frequency. It’s hard to enjoy listening to your station when there’s always a whistle or hum in the background. In the past, I’ve seen some circuits for modifying the Knight to use crystal control, but haven’t run across any lately. If you modified your unit to use a crystal, I’d like to hear what you did, and how it worked out.
My SSTRAN is just fantastic in this regard. There’s no carrier frequency adjustment, yet the unit is right on frequency and drift is imperceptible. I’m never going back to using a free-running oscillator…
Knight Crystal
Yes. Installed it in series with C7 and tuned C9 for max output signal. It worked great.
You will probably enjoy this site:
http://www.knightkit.com/
Neil
That’s very helpful!
Thanks Neil, I’m going to try that! I have a spare crystal at home that I was using with a Vectronics transmitter.
The Knight Kit site is very interesting! I am surprised how many others got their start in electronics and broadcasting with a Knight Broadcaster!
WEAK-AM
Classical Music and More!
More KnightKit AM stuff
WEAK,
I was never happy with the audio quality of the onboard amp. in the KnightKit so I drove the tx. audio backwards through the output transformer and I used a wire wound pot in series with the output to control the modulation. I monitored the modulation with a homebrew “magic eye” tube circuit which I calibrated with a cheap scope (Knight Kit), and my AM radio which was a junk yard Buick car radio I nailed for about 50 cents, but I had to crawl under the dash and remove it myself. I converted it to run on 6 VAC and it was a “hot” receiver…very sensitive and lots of audio power.
My setup was a Scott Kit LK-48 amp connected to an EICO HFT-90 tuner, AR-1 turntable, and VM 714 reel to reel tape recorder. I had wired the house with speakers and built a nice switching system whereby I could send signals to the speakers and/or the tx. This was based on a Stwonger switch which came from a PBX exchange that was being rebuilt. Some fast talking saved this switch from the bulldozer. (The telco destroyed all surplus equipment.) More fast talking gained me permission to carry it out of the plant where I was employed while a college student.
With a telephone dial, I could dial a 2 digit number and the switch would configure the speakers and tx. in various combinations. I thought this was kind of neat.
I still have all the equipment and it all works, except for the Scott amp. Power xfor. went south. The Stwonger was replaced with a patch panel because it became too hard to add or change the wiring.
So, if you have read this far, I guess I haven’t bored you, or as with some movies you keep going hoping it will get better. It is nice to share some oldtime experiences.
Neil
Very Interesting!
I knew I was not the only kid who was crazy about that thing! When I was in high school, a friend whose father worked for Belden corporation brought one into school. The two of us and a third friend got the idea of broadcasting a 1/2 hour program every morning before school. We would meet after school at one of our homes and record the show on a portable reel-to-reel tape recorder. Then we would broadcast it the next morning over the Knight from the math classroom on an upstairs floor with the wire antenna hanging out the window. As I recall, the antenna may have been a little longer than the 10′ specified in the instructions (ahem).
Wouldn’t you know it, the principal got wind of this and contacted the local FCC office. One day not long after, I was invited to come down to his office right in the middle of class. That was the end of our station! But I’ll tell you what– the fellow who owned the Knight became an NBC television news anchorman somewhere down in Bayou country. The second fellow went to work for NPR in the NE and as far as I know, he is still on the air. I’ve had a few gigs as a broadcast engineer here and there, and I work in the electronics industry.
Those things were sure a lot of fun!
WEAK-AM
Classical Music and More!
Principal nuts?
Nice story. What is wrong with that principal? I wonder what motivated him to call the FCC. If he didn’t like what you were doing, one word from him and it would end.
This is hard to believe but it is true. I talked my chemistry teacher into letting me make nitroglycerin! His concern was how I would detonate the stuff. My idea was to put the vial in a field and shoot it with a rifle. He actually considered letting me do this for a few days and then talked me out of it. I am glad he did or I would probably be typing this with my nose.
To tie this into part 15 radio, the blast would probably have been heard farther than my Knight transmitter signal. I know this because of some of my other outdoor “chemistry experiments”. Back then, real M-80s were available and I could buy potassium nitrate at the corner drug store. I did use the part15 AM transmitter to trigger a few of my “experiments” from a safe distance. I protected my transistor radio with a small stack of bricks.
As tech leader for our school play I needed a way to produce an explosion sound off stage. The principal suggested I use the school’s track pistol. I carried that thing around in my pocket for several weeks, to and from school. Nobody cared. How times have changed!
Neil