Why buy something when you can make something? Since you already have coax out there, how about making an antenna from the coax?
The "metal tubing" is the shield of the coax, and the "solid metal or tubing" is the center conductor. So you just strip a long length of the coax, then carefully fold the shield back over the coax. Keep in mind the shield will get shorter as you expand its diameter to fit over itself, so strip it a bit longer then trim it to length.
The whole arrangement should be half the wavelength long (so each section is a quarter wavelength). As an approximation:
$$ \text{length in feet} = 460 / f $$
Where \$f\$ is the frequency in MHz. For your application, \$ 460/495 \approx 0.93 ft \approx 11.2 in \$.
You can cut it a bit long then fine-tune the length if you have the appropriate equipment or through trial-and-error, but that may be unnecessary.
Also, take care to weatherproof the end of the coax. You don't want water getting inside the coax. There are any number of products out there, but some epoxy thinned with alcohol brushed on the end also works great.
Of course this isn't the most perfect antenna design. But if you are getting some signal without any antenna at all, this will be at least an order of magnitude better, and probably, good enough.
The most likely explanation is the new UHF connector you fitted.
UHF or PL259 connectors aren't really suitable for 450 MHz as the 50 Ohm impedance is not maintained through the connector.
Here is a site that describes some experiments, on a pair of connectors the vswr was about 2.3:1. Another site has some graphs showing up to 2.5:1 for various combinations of UHF connectors.
Why did the VSWR change? I can think of a few effects.
First, it's possible your UHF connector, and your soldering, wasn't as good as the original. These connectors vary in quality, it's likely that the antenna manufacturer chose a fairly good one.
Second, the mismatch of the connector will interact with the mismatch of the antenna, which might actually make it slightly better, or worse. It's possible that you were unlucky, and went from a match-improving location, to a worse one.
Cable loss also improves VSWR, so in the absence of any other factors, shortening a cable will increase VSWR slightly. At UHF, a 1 m change would only account for 0.1 VSWR though.
Finally, if your antenna mount isn't well grounded, the coax cable itself might be part of the antenna. Changing the length will change the antenna performance. This isn't ideal, you should ground the mount properly with its screws... If you have a magnet mount, then this might also be happening. It's easy to tell - while measuring VSWR, just move your hand along the coax, starting from the radio. If the VSWR changes, then you are part of the antenna.
What to do about it? You can probably ignore it, and suffer very little impact. The additional loss is well under 1 dB. A radio for 477 MHz with a UHF connector can't expect an SWR of 1.5:1 anyway. 1.7:1 sounds like a reasonably good match for a mobile antenna.
If you want to fix it, the simplest is probably to join the coax where you cut it. You get back the better connector, and most of the old length. It is possible to join coax, but you need to be careful. Here is my method:
- Cut the coax cleanly by rolling it under a sharp knife.
- Prepare both ends: Cut off about 20 mm / 3/4" of outer jacket, without damaging the braid.
- Carefully fold the braid back slightly, trying not to destroy the weave.
- Cut about 3 mm / 1/8" of the dielectric.
- Now tin each of the inner conductors, and solder them together lying side to side. Just let them touch, don't twist them or make a mess. Be quick and use a cool iron, otherwise the dielectric will melt. It melts anyway, so be careful not to stress the plastic until it cools.
- Insulate the joint with tape. First take a piece of tape 3 mm wide and wind it several times around the bare wires. Then wrap one layer of 10 mm wide tape over the top.
- Now fold the braid of one side down over the joint. Use a piece of very fine wire, hair thin, to tie it down, if it doesn't lie flat.
- Fold the other braid down, it will lie over the first braid. It will overlap only about 3 mm. Smooth it down and possibly tie it down with thin wire or cotton.
- Gently solder it in a few places. You're not looking for a massive shiny solder joint, as you'll destroy the dielectric or melt through the tape if it gets so hot. Just tack it in 5 places, letting it cool each time.
- Insulate the whole thing with more tape. Watch out for short spikes of braid that penetrate the tape...
The goal of the above procedure is to keep the cable as coaxial as possible through the joint, and to keep the region of incorrect impedance as short as possible.
You should also try tweaking the antenna length - see this answer for some ideas of the procedure.
Best Answer
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.