CB (27Mhz) Shortened Dipole Antenna
I inherited a very nice base station cb radio...however as you may know I mostly operate mobile or in an apt. That doesnt do well for most RF things. I didnt expect to do much with it but I hoped I could at least RX with it. I looked locally for a mobile antenna I could easily repurpose for an indoor antenna, however the prices were way too high. I instead turned to making a shortened dipole.
I was going to run it vertically so my restriction was room height (roughly 8ft). Using coils I was able to reduce the length of the dipole. Most of the radiation comes from the center outward, so to make the antenna as efficient as possible I moved the coils near the end. Below are the diagrams and notes I used to build it.
The main length of the dipole comes off the center and shield solder joints and is 42" long. Then a 26.8uH coil is needed then a pigtail of 3" is added to the ends...to help tuning and give something to help string it up.
There are many ways of doing a 26.8uH coil. I didnt have any pvc pipe around which is what I usually like to make my forms out of. So I went and got a small jar of kraft peanut butter. Used that to make the coil form then kept it together with duck tape and a few zip ties.
The jar I used was 69.85mm across, you need 24.25 turns of wire which I used insulated house wire (14 guage), it makes it to be just about 8 turns per inch (tightly coiled together) and a rough length of 79mm. I suggest if you dont have those measurement to make several notches in the end of the last few bits of the coil and try several taps to see which is the sweet spot.
This has worked out well for me, with an swr of < 1.5 ...feel free to play around with the design and let me know how yours worked out