A GFCI is always a good idea especially when you have equipment like hams have. Most have some sort of outside ground that they connect the equipment to. If a fault or leakage should get on the chassis of something and you come into contact with it and the outside ground (your antenna connection) that you are hooking up you can get zapped. It doesn't have to be a concrete floor or a wet location.
You may have the cover off working on something and come into contact with the power lead. The GFCI will trip and save you a little discomfort, maybe a lot.

And yes the GFCI looks for a difference in current between hot and neutral. No ground lead needed for them to work.

73
Gary  K4FMX

I am a little late on this post but I just saw the comments here on grounding.

First rule is you want all grounds bonded together.
At the tower you do not want a ground rod "under the concrete". You do not want any metal coming out of the tower base below grade. This will rust and allow rust to creep into the concrete and crack it. All metal coming out of the concrete should be above grade with some slight slope away so water does not collect around it, including tower legs/J bolts.

Assuming you are using J bolts in the tower foundation, tie them to the rebar in the foundation and tie all the rebar in the foundation. Do not weld! Unless you use special rebar that is rated for welding.
This will give a very good auxiliary lightning ground for the tower.

In addition place the 3 (minimum) ground rods around the tower. Do not bond the ground rods to a common point and then run a cable to the tower. Rather run a separate ground lead from each ground rod to each leg of the tower. The tower is the common point for the ground rods.
More ground rods can be added out away from these and bonded to the existing rods.

So far you have the ground rods and the tower concrete base (ufer ground) bonded together for the tower ground.

All cables should be bonded to the bottom of the tower and at the top. You should run a #6 bare wire over to the shack ground. The bare wire will also act as an additional ground radial connection to earth as well as a sure bond to your entrance panel.
There is really no need for polyphasers at the bottom of the tower, only at the shack entrance.

At the shack entrance you want a "single point ground". This is where all of the protection devices are mounted. Any thing that goes into or out of the shack should be directly bonded to that panel including RF cables, phone lines, TV etc. and your AC protectors. If this panel is located very close to your AC service panel that is good. An AC protector in the service panel will do the job. Be sure to directly bond the AC service panel/ground to your single point ground panel.
If your AC service panel is some distance away from your single point ground panel you can run an AC line over near this panel with outlets and protection devices in it and directly bond it to the single point ground panel. This is the cure for having the AC panel a long ways away from your single point ground panel.

Of course now you need another ground field of several ground rods that are tied directly to your single point ground panel as the tower ground system is too far away to be effective here.

All equipment ground leads can run directly to the single point ground panel but you don't need to get too carried away with these ground leads.
The whole idea of a single point ground system is to have a common bonded point for ALL leads entering the shack so that in the event of a lightning strike there is no voltage between any leads. This will prevent any voltage coming in on one line (antenna lead) going to a radio and leaving the radio on another line (power line). If all lines are clamped to the same potential you will not have the equipment (radio) in the middle of a loop.
Now all of the leads may get elevated several thousand volts above ground during a strike (depending on how good a ground system you have) but there will be no difference across the equipment to cause damage.

When installing ground rods, drive them in. do not dig a hole and back fill the hole or use water to wash them in as you loose soil compactness around the rod.

No braided cable for ground connections. It will corrode and not have as good a connection between strands. It is not even good to use inside.
Solid wire or copper strap (best) outside. Stranded wire will corrode at the connections and it is impossible to clean to renew the connection. Large strand cable is ok if cad welding.

73
Gary K4FMX

The diodes in a bridge do not operate in series.

Your PIV is going to be 4044 volts across EACH of the 4 legs in diode the bridge. You should have at least 1.5 to 2 times PIV for each diode leg. That means that you should use 6 diodes in each of the 4 legs minimum.

Do not use resistors or capacitors across the diodes. You can destroy the whole works by doing so. Modern diodes have an avalanche region on the reverse side that acts like a zener diode connected across the reverse junction. It will start to conduct if there is any reverse current and that will equalize any reverse current in the whole string so that one diode does not see more than any other.
With resistors or capacitors, if they change in value at all that can force unequal currents thru some diodes and destroy them. See ARRL handbook power supply section.

73
Gary  K4FMX

Still not correct. 
The old input power on SSB had nothing to do with PEP. It was average power input by plate current times plate volts. Plate current on voice peaks as read on the DC plate ammeter. The plate current meter could not have a time constant longer than .025 seconds (if I remember correct). That power input was limited to 1000 watts.

There was no limit on PEP. PEP could be as high as you wanted. In fact, average power as read on plate current meter peaks is as low as 20 to 30% of actual PEP. So in those days if you had an amplifier that was capable you could have run the 1000 watts average power input with PEP of 5 or 6 Kw input and have been perfectly legal.

The AM transmitters fell into the same boat. They were limited to 1Kw DC input but there was no limit on PEP. Some operators had super modulators that could modulate in excess of 200% on positive peaks while limiting negative peaks to 100%. This gave very high PEP power.

Now of course everything is limited to 1500 watts PEP output.
So while the AM guys lost some power privileges, so did the  SSB guys but few ever realized it as not many understood what PEP really is. Even a lot of the amplifier manufacturers had ads saying that their amplifiers would do 2000 watts PEP input while the maximum it would do on CW was 1000 watts. No way that amp would run 2000 watts PEP on SSB.
The general notion in those days was that whatever the DC  input rating was, just double that and that would give you PEP. Not correct of course.

73
Gary  K4FMX

That goes back a long way! Minimum bandwidth is with all of the rods pulled out. I can't remember what that bandwidth is offhand but I think that with the middle rod pushed in and the two end ones pulled out it was something like 2.7 KHz wide at the nose. All pulled out I think had a sharper nose than that.

73
Gary  K4FMX

Generally it is not the same rating as 1200v ct.
600-0-600 volt designates that the transformer is designed for use with a full wave rectifier with center tap at ground.
A 1200 vct designated transformer while esentially the same transformer, may be rated the same or it may be rated for use with a bridge rectifier.

some, particularly older, 600-0-600 volt transformers may not have insulation to withstand the center tap being above ground.

A transformer that is rated for a full wave rectifier will often have a different current rating than one rated for a bridge rectifier.

73
Gary K4FMX

This may not work well trying to  modulate the collector as in a class C amplifier. I believe that is what you are talking about doing. The conduction angle may be too great (not far enough into class C) to modulate properly.
The modulated amplifier must be operating non linear in order to modulate it. If it is operating in a linear mode it will not modulate.

Sometimes in tube transmitters the driver stage is modulated a small amount along with the output stage. Some tubes do not plate modulate as well as others and adding modulation to the driver stage helps achieve full modulation.

This chip looks as though it is intended as an amplifier for FM signals and you may not be able to control the drive properly in order to properly modulate it.

73
Gary  K4FMX

You are correct that a 2:1 SWR will give an 11% loss of power in a system where the generator source is a 50 ohm resistor such as a typical lab signal generator. In this case most all reflected power will be absorbed in the source resistance of the generator.

This is where "mismatch loss" calculations come from. With a 2:1 SWR in this situation you truly do lose 11% of the power because it is reflected back to the source and absorbed by it.

However a typical solid state transmitter, even though specified as having a 50 ohm output, is nowhere near a 50 ohm source. It is usually a very low impedance and as such it will absorb very little reflected power seen coming back to it.

The transmitter is comonly called a 50 ohm output but what is really meant is that it will deliver maximum power out when it sees a 50 ohm load.

So if the reflected power is not absorbed by the transmitter then there is only one place for it to go and that is to be re-reflected back to the load and dissipated there. If the load is an antenna it will be ultimately radiated.

An easy proof of where reflected power goes can be observed with a wattmeter such as a Bird thru line. you can observe the reflected power in the reverse direction on the meter. You will also notice that when reflected power is present that the forward power reading on the meter will be higher than normal.
Looking at the Bird manual it will tell you that to find the true power delivered to the load you must subtract the reflected power indication from the forward power indication.

As an example with 100 watts out of the transmitter and a 3:1 SWR which is 25% reflected power you will see the meter show 25 watts on the reflected scale and 125 watts on the forward scale. Subtracting the 25 watts reflected from the forward 125 will yield 100 watts of power that will be delivered to the load.

There is really 125 watts of forward power in this situation as the re-reflected 25 watts power combines with the original 100 watts forward power.

Now for simplicity of explanation we are considering that the transmitter is not reducing power due to any reflected power and that we have no feed line loss, which is possible if the load is right near our test setup.

Some small amount of reflected power may be absorbed by the transmitter rather than being re-reflected but that will usually be small.
If a tuner is used at the transmitter before the wattmeter then a near perfect conjugate match can be had and no amount of reflected power will reach the transmitter. It will all be re-reflected. This will also insure that the transmitter does not fold back and reduce its output because of high SWR. With the tuner in place the transmitter will never see the high SWR.

It is interesting to install another wattmeter between the transmitter and the tuner to observe that you really do have only 100 watts output when the second wattmeter between the tuner and 3:1 load indicates 125 watts forward.
Note that the 125 watt reading may be slightly less due to any loss in the tuner.

Reading the Bird wattmeter manual can be very enlightening on the subject.

73
Gary  K4FMX

[/quote]

If a VR tube lights up in the application circuit, it's good.

[/quote]

Not necessarily! I had a VR tube that i accidentally shorted the dropping restor out momentarily. The tube still lit up and seemed to have the correct voltage on it but it did not regulate as expected. With a varying load the voltage would move around about 10 or 15 volts as I remember. After I replaced it with a new tube the voltage was rock solid.

73
Gary  K4FMX

Why do you think that there is a gap in the shield of the loop antenna? If it worked as you propose, strictly magnetic, then there would be no need for a gap in the shield would there.
A screen room would pass radio signals too would it not if we were only dependent on magnetic properties of a radio signal?

73
Gary  K4FMX

DC passing to the antenna will not cause the bird meter to peg, only RF will.
I would bet that you have an open or short circuit on the antenna connection and or an extremely high swr on the bands  that you are seeing the problem on. That is the only thing that will allow the bird meter to read that high. Self oscillation could cause it also if it is taking off on a frequency other than what the antenna is resonant on. That would cause an extreme swr at the oscillating frequency.

Try the amp on a dummy load.

73
Gary  K4FMX

If you believe that a radio signal can get from the outside of a closed metal box to the inside how would you explain why a metal (box) shield used around an IF transformer will not let RF in or out of that shield? Think about a screen room used for repairing/testing radios where outside signals are not wanted inside or the radio under test signals are not wanted outside. They typically have isolation of greater than 100 db. But poke a small insulated wire thru the wall and isolation goes out the window.

73
Gary  K4FMX

I have a BC453 project that I started many years ago. Every few years I drag it out and do some more work on it.
I have added a product detector, IF driven AGC, audio amp, all band converter and power supply.

Look at the converter article in Stoners SSB handbook printed by CQ magazine. It has an all band converter that uses a single 3.5 MHz crystal. The converter is double conversion on all bands except 80 meters where the first converter acts straight thru as an additional RF amplifier.

All of the bands above 80 meters are converted down to the 80 meter band which helps the image problem. The 3.5 MHz crystal will let you tune from 3700-4000 on 80 meters. on the higher bands the first converter works the same and in addition there is a harmonic multiplier to make use of 7, 10.5 etc for the other converter.
The first IF has a bandwidth of 300 KHz (from 3.7-4.0) which the BC453 tunes across.

while the concept is neat it doesn't work quite as well as Stoner says it does. If I remember right he claims that you just add the dial on the 453 to the crystal injection frequency to read where you are. But if you use the injection harmonics that he shows in the article you will be tuning backwards on some bands. There are also problems not only with imiges spaced by twice the IF frequencies (both the 200-500 KC and the 3.7-4.0) but also problems with the harmonics of the 3.5 oscillator causing reverse imigaes to be present. Think about high side injection and low side injection at the same time due to the crystal harmonics!

My latest change was to add a different, second, crystal for the higher bands that operated at higher fundamentel frequiencis so that the harmonics of it don't cause high side and low side injection at the same time.

I am also working on adding gang tuning of that variable 3.7-4.0 IF to eliminate imigas on the conversion to the BC453. That seems to work pretty well but it adds another knob to peak in addition to the front end ganged tuning.

It is a fun project and can be made into a very nice sounding, very stable receiver that you can directly read out the frequency on.

By the way, using an 80 meter command receiver as the front end is not great as they were never very stable and dial readout/tuning is something left to be desired compared to the BC453.

Mine is all apart now in a box where it will probably stay for another couple of years until I get the bug to work on it again.

73
Gary  K4FMX

Hi Jim,

It is difficult to really measure IMD with a receiver by just listening. If we are going to do comparisons of amplifiers then a narrow filter of a few hundred Hertz is required.
Agree that the S meter will respond to PEP but doing that with a regular SSB filter not only gets the PEP value of the two tones but it may also include some of the IM products added in too which will increase the apparent PEP.

I contend that there is no easy way to measure PEP on a spectrum analyzer because the bandwidth would have to be wide enough for the modulation envelope and that could include some IM products.

by using a narrow band filter and looking at each tone individually and comparing to each IM product individually you will get the true IM level difference.

When measuring IMD it is important to use tones with enough spacing so that you can see each individual IM product separately. If the tones are too close together the IM products may fall too close in and you will not be able to accurately measure them.

For voice modulation which contains many tones spaced close to each other, many of the IM products will fall within the band pass of the receiver while listening to the wanted signal. As I have mentioned earlier and I think that you have too, switching side bands on the receiver will reveal close in IMD products.
On the wanted side band those IMD products add to the wanted signal and slightly increase PEP of the signal as observed.

My point being if we are to accurately measure IMD products a good standard needs to be followed in order to compare one amplifier to another.

73
Gary  K4FMX