sears-roeb: Silvertone Model 4464
I am in the process of restoring the title model radio, can someone provide me with the type of antenna typically used with this radio? Under what conditions or type of antenna would the antenna ground terminal be used?
A loop aerial is best to avoid LOCAL interference, it uses both connections and is a big subject, try 20 turns any kind of insulated or enamelled wire on 12" approx non-metal frame (any shape, a picture will do). Otherwise a wire 6' above a curtain or 20' outdoors, then you can try an earth wire either to water / heating pipes or a 4' spike/pipe in lawn or flower bed if you are not in an arid place.
I wound 20 turns of 28 ga magnet wire on a 14" dia.embrodery hoop about 1/2 inch wide. Based on your 12" dia. form the overall length is maybe equal to 23 turns wound on a 12" form. The directivity inproved and therefore the reception along with reduction in background static noise; however, it did not do much to improve the shortwave reception. I have not tried the 6' long wire, although I have experimented with different length long wires, but none as short as 6' and no earth ground which did nothing to reduce the static background noise. The radio came to me with a 12" wire connected to the antenna terminal and is totally inadequate after replacing all paper caps, the 6A7 tube, and realighnment. I suspect a good earth ground would be required with the long wire, but my work space is not located where I can get to a good earth ground.
The radio owner is not probably interested in the shortwave bands, but I do want to show him how important the antenna is to AM radio reception especially in todays digital world.
Loop aerial would need to be only a couple of turns and large for shortwave. Also it's narrow band so would need tuned.
See this Philips with multiple single turn loops disguised as beading, switched in different configurations on the different bands. It has remarkable SW performance without an aerial.
My instructions were only for MW/BC band. I'd not waste an embroidery hoop, but use a card box, or a card with slots or a deep photoframe/picture frame. On some sets adding a tuning capacitor to the loop works well.
I have a 20t loop for MW with no tuning on a modern LW/MW/FM tuner, Mitsubishi M-F520. It's a $3 approx picture frame about 6" wide and 16" tall. The wire wound on a card frame. A slide switch is fitted on the rear to add 2mH in series for LW. Perfect UK LW during day and the UK MW at night here in midwest of Ireland. The VHF-FM uses a separate pair of wires on a 300 Ohm to 75 Ohm adaptor.
For a valve set with SW:
I have two pieces ot panel board cut to fit in a cross shape, about 14" across. This is on a stand orientated diamond style. There are three sets of wires wound with 1/32" to 1/16" gaps (about 0.6mm) . On MW they are in parallel, which gives more Q. On LW they are switched to series which gives about x9 inductance (N squared).
I have wire loosely coiled around the wire loop (thus at right angle) with one end to aerial or earth end of coil and the other to a wire across the window. On LW/MW it mostly picks up interence and as it looks like one turn in parallel open to a pick up wire, then it can cancel interference as it will be poor to pickup LW & MW EM, but pickup local E field. On SW it's like a whip aerial loaded by a series coil, the main LW/MW coil is high impedance on SW and has no effect. On MW / LW the SW wire coiled around at right angles is like an electrostatic shield, which reduces local electrical interference.
See the three aerials on the drum on the French set. It has vertical MW and LW coils at right angles so as to not interfere and a third wire as electrostatiic shield on the third right angle around the drum.
I also have a Vidor set which has a single turn SW loop at the front as well as the normal LW/MW loop at the rear. If does pickup the stronger SW stations with no external aerial. It's pretty good on LW & MW.
In general, SW needs a 3m long to 20m long wire for decent performance, with matching of the wire. The Telescopic aerials are rarely more than 1.2m / 4' and thus pick up a lot of interference. Most cheap modern sets need an attenuator (built in on my VR500) if a decent external wire is used. Loops are best, but on SW they need to be tuned and only 1 or 2 turns.
Thanks Michael for your input.
After trying the loop antenna design; not preferred by the owner and he did not want to string a long wire, I came upon an active AM broadcast antenna tuner in the March 1971 issue of Electronics Illustrated using a ferrite loop antenna. Although not period, the owner as mentioned is not interested in the shortwave bands. I managed to find the parts, including the ferrite loop antenna, although not the part in the parts list, I decided to put the tuner together, not knowing if it would work with the Silvertone since my understanding is these old long wire radios need to be modified to make the ferrite loop or traditional loop antennas work. The tuner gain is 40db and works with 50 to 1000 ohm radio input impedances.
I hooked the tuner to the radio and I was surprised the tuner made the radio boom like no other. It was like turning on a light bulb in a dark room. The tuner works so well you have to be careful you do not overdrive the radio into distortion on strong local stations. As a DX'er this tuner would be ideal as the ferrite antenna is rotatable to help discriminate same frequency stations.
The tuner is small in size, 5-1/4" X 3" X 2-1/8" aluminum box that can sit on top of radio or hooked on back, out of sight, with only the rotatable antenna exposed above the radio top.
On a personal level I may try to investigate shortwave loop antennas that are small in size, but I will not have the Silvertone very much longer to use as testing unit. If the radio were mine, I would incorporate a selectable loop antenna switch.
A ferrite rod is just a compact loop aerial. You don't need a complex active aerial.
Anyway, at least the owner is happy.