I took a look at W1HUE's article in The ARRL Antenna Compendium, Volume 2, and it looks like the standard formulas for inductance and capacitance hold; that is, capacitance is the coax's characteristic capacitance per foot, and inductance is calculated the same as if it were one solid conductor (i.e., not one conductor within the other, as in coax). What Larry did in his article to present a BASIC computer program that took inputs of coax diameter, coil form diameter, coax capacitance per foot, and trap frequency; and provided number of turns of coax for the trap, the length of coax needed to wind the trap, the amount of capacitive and inductive reactance, actual capacitance and inductance, and an "effective" length (the amount of length to shorten the next leg of the dipole by).

Obviously, Larry wrote the program back in "the day" when most hams had BASIC packaged with their computer's DOS, but it shouldn't be difficult to convert the BASIC listing to Excel. If you still have BASIC somewhere in your computer, you might try requesting EAST.BAS from either Larry or the ARRL.

By the way, I recall two different ways to make coax traps, but I'd have to look at my notebooks to find the differences. You might research the following issues of QST: May 81 and Dec. 84, and Ham Radio Oct. 1981. The construction method Larry used was to connect the braid of one end of the coil to the center conductor of the other.

FYI - Stew

Good quality PL-259 hardware speaks for itself. I swear, some of the plugs I've seen were chrome or nickel plated, and wouldn't solder worth a flip. I found that by drilling out the solder holes, making them a little larger, and scraping the plating away from the copper or brass underneath, made attachment much easier.

I have found that resistance soldering is a fast way to heat up the barrel quickly. Take the heating element out of a 140 watt or so solder gun, then hold the gun's two prongs against the PL-259 barrel and pull the trigger. The solder should melt within seconds.

FYI - Stew

As an aside, I believe in George Hart's account of the early days of Field Day, it was all scheduled on local time. That meant the folks in New York, for instance, got a three hour head start over Californians, but would have to stop three hours sooner. In those days, when Field Day was mostly about message handling, the east coasters racked up the most messages sent, but the west coasters got points for most messages received.

Time is based on the Prime Meridian, which runs through England. If it's one minute past midnight on Wednesday at the Prime Meridian, it's 2301 the night before (Tuesday) just 15° of longitude further west, and so on across the western hemisphere. So, even it is two hours into Wednesday at 0200 UTC, it is still late Tuesday night across the Americas.

Like, when it's 1 a.m. Wednesday in Miami, what time is it in San Francisco? You'd back off three hours, so it would be 10 p.m. there, and it would be yesterday, so it's still Tuesday for the left coasters.

This is one reason DX chasers have to be careful in keeping their log dates caught up with UTC time. Imagine trying to claim a QSO with someone you know you worked, but they report you're not in their log. One of you may be a day off, simply because his Wednesday is your Tuesday.

Also, UTC does not change with daylight saving time. To further complicate matters, countries in Europe do not change their dates for daylight saving at the same time, and some don't change it at all.

Good luck! Several ideas: 1) check local antique stores and at ham flea markets; old hi-Z phones sometimes turn up. 2) make a set using old-style 600-ohm telephone headset earphone pieces. 3) check www.tubesandmore.com or www.midnightscience.com for crystal earphones. Cost is around $4 each, plus S&H. 4) build a hi-Z to low-Z amplifier. Many op-amp circuits will work, and I have several designs for simple one-transistor impedance converters.

Idea 1) would be coolest. Old Alnico, Argonne, Trimm or Murdock sets would offer the best bang for the buck (Alnico's have a 5000 ohm DC resistance, 16,475 ohm Z at 1 kHz, 0.2 mV MDS and on as little as 2.4 pW of power! At one time, Fair Radio Sales sold the Murdocks as their model HS-23 phones. They had about 2000 DC ohms, 9300 1kHz ohms, 0.2 MDS and 4.3 pW threshold.

A cheap earcushion, and one I used in the Air Force, is to cup each earpiece with cloth sports wristbands.

Flat black works best.
That's why stealth aircraft are black
-----

The aircraft are black because that's the color of the radar-absorbing material they're covered with.

FYI - Stew

Ask yourself this, "If maximum power transfer, from source to load, occurs when impedances are matched, would matching these impedances help?" I can tell a difference between not using a tuner and using one; but when I took my shortwave receiver on various world travels, I never took a tuner, and I got along just fine.

As to antenna terminology, a non-resonant antenna is one that has no standing waves because it is terminated in its characteristic resistance, and terminated antennas are somewhat directional. Off-resonant antennas are those that do have a resonant frequency, but are not being used at that frequency.

Okay, Danny then. You have a computer, you can look up the rules yourself. I gave you the FCC authorization site, and you can peruse the Title 47 Part 15 rules at the GAO web site. As for your one tube transmitter, you're okay. At least one of the rules states:

"Title 47: Telecommunication
PART 15—RADIO FREQUENCY DEVICES
Subpart A—General

"§ 15.23   Home-built devices.

"(a) Equipment authorization is not required for
devices that are not marketed, are not constructed
from a kit, and are built in quantities of five or
less for personal use.

"(b) It is recognized that the individual builder of
home-built equipment may not possess the means to
perform the measurements for determining compliance
with the regulations. In this case, the builder is
expected to employ good engineering practices to meet
the specified technical standards to the greatest
extent practicable. The provisions of §15.5 apply to
this equipment."

Enjoy your hobby, Stew

Daniel,

As a ham for 25 years, you know that FCC rules cover more than just Part 97, and we hams are responsible for complying with the whole Communications Act. As hams, we can build our own equipment without seeking equipment certification, and can build kits, and even modify radios that were designed for use in other services, and as long as they are operated by hams in the ham bands they're legal.

But manufacturers of radio equipment, including ham radios, must have their product certified and authorized by the FCC before that equipment can be sold. If the UHF radios that were purchased over the Internet don't have the FCC Identification Number on them, then they are in this country illegally. If they do have the identification number, then the manufacturer's information is available at the FCC web site under that number. Procedures for authorization are not in Part 97, but a good starting place to find more information about the process is at http://www.fcc.gov/oet/ea/.

FYI, Stew - W5FYI

Ditto on certification. If there is indeed an FCC acceptance number on the devices, manufacturer's information will be at the FCC web site. If there isn't an FCC number, somebody got took.

This should tell you something: "I'm guessing that most of the variable capacitors I have knocking around in the junkbox (age between 30 and 70 years old) are either aluminum, brass, or some sort of plated steel for the plates."

I agree that brass is probably best, from the workability and durability standpoint. Silver plating using photo fixer is viable if you electroplate and not just "dunk plate."

If your capacitor is for a high-power tank circuit, you should strive for the best electrical contact between vanes and rotor and plates and frame (e.g. welding or brazing the parts together), and keep the plate edges smooth to avoid potential spark gaps.

Just my 2¢ worth. Tell us more about your project.

I did the math and got 1.08 dB, (using base 10 log).

OK, so there's technical problems to work out for capacitive coupling to work; micron-thick crystalline aluminum oxide dielectric? Teflon-coated steel tape passing through a trough of mercury? Something's bound to work, at least in theory.

I had thought the tensioning spring would add inductance, and if it's in a metal housing it would be somewhat lossy as well. But since this is a poor man's project, it just might not matter all that much.

It seems to me that a capacitive connection to the metal tape would do it, so you really wouldn't have to strip the tape to bare metal. A piece of insulated printed circuit board arranged near the tape, so there's about 0.1 µF of capacitance between the tape and the pcb, should work quite well.

FYI, Stew

Adding extra coax could have reduced the apparent SWR through line losses. On 80-meters, 1.2:1 means you are losing 0.82 watts, or less, for every 100 you pump in. At band ends, 4:1 SWR means, at worst, you are transmitting 76 watts (probably a lot more, due to reflections). The theoretical vertical (36 free-space ohms) would exhibit about 1.4:1 SWR to 50 ohms, so your 1.2 SWR indicates some antenna, ground and line loss.

A 3.5:1 SWR on 20 meters would still radiate more than 70 watts out of ever 100, probably a lot more because your coax would only attenuate about 0.4 dB of the signal, and transmission line reflections would increase the radiated power somewhat.

If you need lower SWR to "protect the rig," think about installing an antenna tuning unit (antenna tuner) in the shack.