[patmat2350]

blacks and reds, oh my.

First, sorry, searching here on "antenna" yields a bizillion results but I haven't yet cleared up my foggy understanding of antenna technology.

- Is there a primer anywhere here on the basics of antennas?
- Does any of the Philco lit tell the user how to connect Antenna, Ground, and Red & Black? And what are those even for? (I haven't found any info here yet).
- I see lots of "advice" in various places, with little explanation. Like ground the radio but don't use house ground. Huh? Why not?
   - Speaking of grounds... is it advisable to install a new grounded power cord, connecting the ground to chassis?
    - Speaking of new cords, if a new polarized plug is used, does it matter where the neutral and hot wires go?

[MrFixr55]

Hi PatMat

What model radio are you dealing with?  Is it transformer powered?  AM Broadcast only or shortwave?  FM?

Radios that require an external antenna usually have a tuned circuit that includes an air core transformer "antenna coil".  The primary connects to antenna mad ground.  the secondary is tuned and connects to the grid of the 1st RF amp or 1st Detector (Convertor or Oscillator / Mixer).

If the radio has 2 wires for the antenna, one should be hooked up to an "Inverted L" (more later), and the other should be connected to a "ground" such as a cold water pipe.  Connecting to the electrical supply ground may or may not inject a hum.  If a separate ground rod is sunk, some recommend bonding it to the electrical system ground, some don't.  It depends on local codes, ground moisture, etc.

If you can find the owner's manual for the radio, there will be recommendations for antenna and ground.

I believe that an "inverted L" antenna is directional for reception, with the strongest direction being opposite that where the lead -in wire is connected.

As to the length of wire, ideally, if it is end-fed, ideally, it should be "1/4 wave", in other words, the length of the wire should be 1/4 the length of the wave.  Therefore, for the AM Broadcast Band (assuming 1000 KHz has a wavelength of 300m, the wire should be 75m or 225 ft.  This is not practical in most places.  Fortunately, for short wave bands, to have a 1/4 wave antenna is a lot easier to erect, and unless you are trying to get distance records for AM, a 75ft antenna will do very well.  For local stations, even 25-50 ft will do well.  many apartment dwellers routed an antenna around the perimeter of the ceiling of the room, hidden by moulding or a "picture rail".

Standing waves affect the efficiency of the antenna.  Attached below is a treatise from RCA regarding the best lengths for antennas depending on the band or frequency:

Antenna Length Chart.pdf Size: 74.46 KB  Downloads: 170

As to a grounded or polarized plug, you definitely need the schematic of the radio.  If transformer powered, ensure that the switch is on the "hot" side (narrow blade) and the unswitched side on the neutral side (wide blade).  Ensure that the any fuse is also on the hot side.  Filter caps should be across the transformer primary after the switch.  If there is only 1 cap between the transformer and the chassis, it is safer if that cap is on the neutral side.  Ensure that you are using "Safety Caps"

If the radio is a "hot chassis" type without a power transformer, then some rewiring needs to be done.  For some reason, possibly doing with minimizing hum, the power switch on AC-DC radios was always placed at the "neutral" side of the radio.  These same radios had either a 0.05 - 0.1 uF cap and 10K resistor connecting the chassis to the neutral sidefor RF coupling, or the neutral side was directly connected to the chassis.  If the switch was on and the plug was connected so the chassis was on the neutral leg, then there would be no shock WITH THE SWITCH ON.  However, with the switch off, the chassis now becomes dangerously hot due to the flow of current from the hot leg through the now cold, low resistance tube filaments.  The following rewiring makes the radio safer (This procedure is not possible if a working "Cordohm" power cord will remain in use):

• Disconnect the wires from the power switch.  Note that often that the ground side of the volume control is connected to the load side of the switch also.
  
• Put the switch on the "hot" side (input to the rectifier plate and heater).
  
• Connect the "neutral" wire of the power cord (wide blade) to the load connection and volume control low side connection removed from the switch this usually connects to the common B- and low side of the 1st AF tube's heater.  This also connects to the aforementioned capacitor that couples the chassis.
  
• If the radio uses a "Cordohm" (sometimes referred to as a "curtain burner") where a tube heater dropping resistor is contained in the power cord, this feature must be substituted by either a resistor or suitable AC electric capacitor.
  

Hope this helps.

[Chas]

- Is there a primer anywhere here on the basics of antennas?
- Does any of the Philco lit tell the user how to connect Antenna, Ground, and Red & Black? And what are those even for? (I haven't found any info here yet).
- I see lots of "advice" in various places, with little explanation. Like ground the radio but don't use house ground. Huh? Why not?
   - Speaking of grounds... is it advisable to install a new grounded power cord, connecting the ground to chassis?
    - Speaking of new cords, if a new polarized plug is used, does it matter where the neutral and hot wires go?

Wikipedia has several explanations on antennas. Be aware that many antennas mentioned are resonant by design to match a transmission line to the radio. If a domestic receiver has the option of two antenna connections then a transmission line can be used, with or without a ground. Most often that line is a balanced twisted pair, common wire in the 30's but can be easily replicated with modern wire. The twisted pair is roughly 72 ohms impedance, its connection to the antenna is specific in design such that the antenna "delivers" 72 ohms. Such an arrangement keeps the reception confined to the actual antenna and not the transmission line. Resonant antennas can be directional.

The most common antenna for receiving is the aperiodic and mostly non-directional, depending on what frequency is to be "listened" to (tuned) that antennas impedance varies widely. For BC reception the best results is that the lead-in (single insulated wire) is mostly vertical of some 20 to 50 feet but any vertical component is good.

The house grounding system is for protection from electrical faults not for the facilitation of RF, it is NOT a one-way street but has the connected noises from all the electrical device that are on the home circuits. It will introduce noise in most instances and instability in early regenerative radios.
Radios provide RF bypassing to the line in most models, ground the chassis to yhe AC line defeats the purpose as would using a polarized cord where none existed. Some radio models advise reversing the (plain) power cord if the radio has noises.

Only communications receivers (some) use a 3-wire grounded cord.

The antenna is only half the receiving equation, the other is the ground in most aperiodic antenna installations. That wire to EARTH should be as short as practical, can use a homes metal water plumbing if need be.

The result obtained from a outdoor antenna vary widely, all lightning protection must be followed.  Often protective covenants prevent an outdoor "visible" wire, so stealth means have to be used.

Often defaulting to an indoor loop antenna is the only answer, that too, is full of "landmines" Best suggestion is either build or buy a simple loop and experiment often it will work satisfactorily. Antennas will also vary when used for short wave generally much more directive.

GL

Chas

[patmat2350]

Many thanks, let me digest all that!

It's a Philco 655 in a 645k console. The 655 has AM BC, SW & police bands.

Schematic is here, yay, but I haven't found a manual yet. It has a single clip each for ant & grnd, and screw terminals for red & black. These are all grouped together on the schematic.

House ground is of course bonded to a ground stake, so would any hum in the house ground be due to proximity to the AC wires, yet not be strong at the ground point itself?

Polarized plugs etc: Obviously the radio is designed to function with a nonpolarized plug, but it sounds like some thought is needed before connecting chassis ground to house ground. Thx again!