2024-T3 is probably the most common aluminum sheet available.  Quite stiff, easy to work.  So would be a good choice.  T1 is quite bendable.  Would probably work in a cap, but I think T3 is a better choice.  2024-T6 is even stiffer than T3, and for this application would be find.  Doesn't bend well, but likely not a factor for you.  7075, 6061 are also fairly common aluminum alloys, and also available in the various T's.  All would work.

.050 is a good compromise thickness for strength vs thickness.  If you go with T3 or T6, .032 should also be fine.

I have had good luck going to a metal scrap yard and finding some scrap sheet aluminum.  Most all is stamped (with ink) as to the alloy.  Also T3 is obviously stiffer than a T1 or T0.  T6 is usually heavy weight due to the alloy.  After you cut the aluminum, it would be good to round the edges very slightly to eliminate any small burrs that could cause arcing.

I seem to recall an old article in QST about making variable caps.  You might try a search on the ARRL site.

SOunds like fun, good luck.  John

I have always visualized a vertical as 1/2 of a dipole, with the other half being the radials.  Thus when you eliminated one half of the dipole (resonant on both 80 and 40), and replaced with radials, you "messed up" the resonance on 40 of that missing half.  The radials, being longer than 1/4 wave at 40, have a high reactance at 40.  

Assuming this is true, your SWR on 40 is high because the vertical side has about 36 ohm impedance, but your radials are presenting much higher impedance.  The sum of these two impedances is much higher than 50 ohm, thus high SWR.

So adding some 40-meter resonant radials (1/4 wave) would re-establish the 40 meter resonance on the missing side (ground).  

Anyway, that's my take on it.  Good luck.  John

I have a log home and, as you might suspect, the logs to shift slightly from time to time (mostly temperature, I suppose).  When this happens I hear a fairly loud "snap" that might be similar to what you have heard.

If so, the cause might just be your roof rafters shifting slightly.  And being in the loft, the sound would be easy to hear.  Another possibility, of course, would be the cold air return, with a crimped (fold-over)joint shifting (again likely temperature related).

John

If there is any way to mechanically mount both antennas in parallel, you would have the best of both.  The 20M will appear to be a high reactance when operating 40 (and therefore mostly out of the circuit), and vis versa.  Sort of like two parallel dipoles.

Thanks for above comments.  I have just purchased a used Daiwa RF440 (external RF processor).  Hope it works ok.  John

I'm wanting to add an RF speech processor to my KWM2A to enhance ability to work DX.  There are several models of older vintage that might work fine, including Comdel, Magnum 6, Drake, DX Engineering, and probably some others.

Does anyone have recommendations as to which model(s) work best with KWM2?  Thanks.

I purchased from ebay a few months ago a Collins Radio 35C-2 low pass filter.  Have also seen some others from time to time for sale, selling from $20 to $40.  This filter has 80 db rejection!, less than .2 db insertion loss (I've tested this using watt meters), and will also handle MUCH more than 1500 PEP (I have tested into dummy load at 3KW continuous with absolutely no heating).  Very heavy all-brass, silver plated.  Uses door-knob caps (much more expensive).

A golden-oldie, but built to last, much better than any of the higher-power filters I have seen on market today.  If you can find one, you will be satisfied.  John

Is it true that you have to know code to use a fan dipole?

For what it is worth, I have purchased Chinese 6146B's and 572's from Penta Labs, and am very satisfied.  Saved money.  6146b's neutralized at same point as Sylvania versions and slightly higher output.  Ditto for the 572's.  

My experience, however, might not be applicable to the 3CX800's.

There also seems to be a supply now and then of the pulse version of the 3CX800's at prices around $300 or so.

John

I agree with the above suggestions about checking the contact alignment.  Having done that, you still may have problems.  For relay contact problems the best method I have found is to cut a strip of cardboard (business card is perfect), then spray on some brake parts cleaner (buy at auto parts place).  Place cardboard between contacts and press down on the key knob.  Slide the cardboard back a forth a few times.  Repeat with clean part of cardboard if necessary.  Brake Parts Cleaner is a very powerful cleaner.  I have not had problems using, but do recommend not allowing to stay on plastic.  It may also remove markings.  Then for relays (and switches) I spray some standard contact cleaner since it has a lubricant that the brake cleaner doesn't.

John

Pins 1 and 4 (the big ones) are filament.  Pin 3 is grid.

John

I like the idea of taking calls "by the numbers".  Being in Colorado, it is not unusual to get beaten out by the east coast due to propagation (east coast reports of 20 over 9 when I'm hearing the DX station at S5).  So gives the rest of us a reasonable chance.

Like the other comments, I think it is vital that the DX station retain control over the pileup.  And split frequency usually keeps the long-winded callers more under control.

Enjoy your adventure.  Hope to work you.  John.

Change the power cord on the 830 to 3-prong so it will connect to the ground on your 120 volt circuit.  From safety perspective all of your equipment would then be grounded, just like other 3-wire devices plugged into power.  Like above post, not sure why the concern about lightning ground on an attic antenna.  If lighting is going to strike, it probably already has a bunch of stuff in the attic to hit.

With or without a ground, it is a good idea to disconnect antennas from rigs during storms.  Even without direct hit (unlikely), static buildup can damage components.

I remember seeing some earlier posts from you regarding other start-up questions.  Nothing wrong with that, but you might also find it very helpful to check out a local radio club and see if you can become acquainted with some helpful members.  There are so many little hints that can be make your start-up go smoothly (and may save you some money and frustration).

If you haven't already, go to the www.arrl.org site and click on the "clubs" link to find a club near you.  

Best of luck.   John.

There might be bypass capacitors connected between each side of power and chassis.  If so, that could cause a voltage potential on the chassis.  As noted in above posts, replacement with 3-wire cable would probably solve the problem.  If not, you might have a bypass capacitor that is leaking, and needs replacing.

By the way, buy a cheap power strip, cut and use the power cable for your replacement.  Nice molded plug, good wire, and cheap.