All transmission lines suffer some loss, you will never get as much power out at the far end as what is put in at the source. This is true for both transmitters as well as receivers. For direct current (DC) the loss will be the resistive loss of the wire or other conductors used. At higher frequencies the resistive losses still occur, but other losses occur as well due to the dielectric loss which increases as the frequency increases and is generally much higher than the resistive loss.
In coax the dielectric is generally some sort of plastic located between the center conductor and the outside braid.
Balanced line may come in the form of twinlead,
ladder line
or open wire line
With a balanced line the only reason to have anything at all between the two conductors is to maintain a uniform spacing and for this reason the less material the better. This is also true of coax, but much harder to implement in practice. Further there is generally a greater distance between conductors in all types of balanced lines than with coax.
Generally air makes a much better dielectric than any other substance when size is not an issue since free air does not degrade over time. It is the nature of the dielectric which primarily determines the signal losses at radio frequencies and as the ARRL handbook pointed out, losses for coax are higher than for balanced lines and the higher the frequency, the greater the advantage.
As a side note, the preceding assumes a perfectly matched line, in other words the source impedance = the load impedance = the characteristic impedance of the line. When there is any sort of a mismatch, a standing wave ratio (SWR) will be greater than unity and losses in coax will increase dramatically with an increase in SWR.
You are quite correct that the loss per foot for open wire line at these frequencies is far less than coax; if it is properly installed. This is a big if. The first thing I would check is the type of coax you are using. Is it some cheap, generic stuff from a place like Radio Shack or is it a premium quality product from a firm like Belden designed specifically for low loss at UHF frequencies? Your ARRL handbook lists loss for different types of coax.
Another thing to try is a mast mounted preamp at the antenna. It is better to boost the signal before the transmission line rather than after.
Getting back to how to best install open wire line, it should run straight in free air from the antenna to where it enters the building. Taping it to a metal mast, bending around corners, running it through walls etc. will all cause it to perform in a far from ideal manner. Coax suffers far less from such treatment.
A lot of questions but if you are looking for a WWV receiver design here is one and below is one of the circuits contained on the link: -
- Do I need any special length for my antenna?
YES but it's probably not too critical if you are receiving a decent signal. A quarter wave dipole at 10MHz is optimum but this will be 7.5m long so try a couple of metres.
- Can any inductor/capacitor combo be used that meets the LC resonance
frequency equation? (C=100nF, L=50.3uH, should resonate at 10Mhz)
NO, you need to tailor the inductance capacitance ratio to give a decent Q factor but not be susceptible to parasitic components. Try for a resonant circuit that uses no less than 50pF - 50pF and 5060nH resonate at 10MHz - if you half C, double L for same resonance at an improvement in Q of 2:1. BTW it's "M" not "m" in MHz
- I'm guessing this is tied to the output voltage or current of the
antenna. How would I calculate this?
Tricky, suck it and see
- Would amplification between any step be useful for final input on my
Arduino? (Antenna->LC->RC->output->Arduino)
See design linked to for best guess at what you should be aiming for.
- Would I run the output into another LC->RC circuit tuned to get the
sub-carrier? Does an LC->RC circuit even work for dual-side-band? (I
honestly couldn't find a difference between normal AM signals and AM
DSB)
WWV uses up to 100% modulated AM (or normal DSB) transmission. Use a diode detector (as per link) to produce the demodulated waveforms.
Best Answer
Ok, doing a little work with the calculators found here and here, I came up with an idea that I think you might like.
Materials:
If you ground one end of your primary (50ohm) winding on the input transformer, you can then run an unbalanced coax line to a "loaded quarter wave" antenna that can be made resonant with a 50ohm impedance for our band of interest. FYI: AM broadcast band reaches across nearly 2 full octaves of bandwidth (0.5MHz-1.7MHz), so it's not very well possible to receive the whole band resonantly with a 'fixed' antenna.
Construction:
OK, that took a bit more explaining "on paper" than I expected in my head, but if you get this far, you should be ready to "fire her up." Start out with the tuning slug mostly outside of the inductor, then tune to a high-frequency band AM signal in your area & adjust the tuning slug for best reception. More slug in the coil = lower frequency tuning for the antenna, so if you can't get the high-frequency station to tune in 'great' at any slug position, try tuning to a lower station; if that works, remove metal filling from the slug as necessary.