I have been trying to imagine how to achieve a horizontal dipolar antenna for the C.Crane.
The answer is...
From the link posted in Reply #2:
It is possible to install the antenna either in horizontal or vertical position, allowing ease of installation in restricted areas.
SPECIFICATIONS Impedance: 50 ohms Type: Dipole, Polarization: Vertical, etc
Can anyone explain how a linear dipole installed with its elements in the horizontal plane can be specified by its supplier to be vertically polarized?
PS: Wouldn't changing the antenna of a Part 15 FM certified transmitter void its FCC certification?
The certification process exists for manufacturers to build legally saleable products under the FCC rules.
Once legally offered for sale the certification is fulfilled.
The purchaser of such equipment becomes responsible for upholding part 15 rules whether his equipment is certified or not.
The idea that an owner of such equipment can "void" the certification is fallacious.
If the certification were literally voided the manufacturer would need to recall the product and face violation notice or fines for selling uncertified equipment.
The only legal way to sell fully-built low power part 15 transmitters is to have them certified.
The only way to purchase an already built part 15 transmitter is to buy a certified one.
I always have been trained to think that dipoles were around 70 ohms.
I believe the dipole antenna supplied with my Technics Receiver uses 75-ohm flat-wire with a 75-ohm balun to whatever the unbalanced antenna jack is... guessing 50-ohms.... darn, I can't find the file on that.
But for a transmitter I would think that when the SWR is minimized on a particular setup, then you've got an impedance match whatever the impedance happens to be.
The fun part begins for me now, as I wait to become better informed.
Yes, about 70 ohms for the traditional 1/2 wave dipole which really works better at about .47 to .48 wavelength.
It should be fed with balanced feedline which is why a balun is usually used with unbalanced coax at the feed point to prevent RF currents flowing back on the outside of the shield which skews the radiation pattern.
A folded dipole impedance is around 300 ohms which is great for use with balanced twin-lead (typical old style TV antenna.) An impedance matching balun can be used with unbalanced coax to match the impedance of the antenna to the coax and convert balanced to unbalanced feedline.
The feedpoint impedance of a dipole will change with relation to the distance above ground.
The dipole can be used at odd multiples of the fundamental frequency. For instance a 7 mHz dipole works great at 21 mHz.
This shows a dipole which is 3 half wavelengths, an odd multiple of the half wavelength. The graph shows the feed point would have a low impedance at resonance (low voltage-high current.)
When I said 75-ohms I meant 300-ohms.
When I said "flat wire" I meant twin-lead.
And indeed, as gambled, fuller information arrived.
Thank you sir for your service to the lower power.