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Vintage tube radio antennas, 1930's

2jackmans

New in Town
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2
Is a long wire antenna directional?
Does the signal enter the antenna at right angles or straight on?
Would a circular long wire antenna, say 40' or more longer pull in signals from all directions?
Would a coaxial cable from the outside to the inside terminating at the radio be best to eliminate house generated interferences?
What size coaxial cable would be recommended if at all, i.e., RG8?
 

LizzieMaine

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A random long wire less than 100 feet or so isn't going to be noticeably directional on distant stationsm but you may notice some directionality on noise pickup, depending on how close you are to the noise source -- a power line, a transformer, etc.

The lead-in that'll give bnest results will depend on the radio. Look at the antenna terminals -- if you see two screws and a ground screw, the radio was designed for a transformer-fed twisted pair lead in. These types of "noise reducing aerials" were very popular during the all-wave craze from 1935 onward, and I can personally testify to their effectiveness. The matching transformer that comes with the aerial kit is essential, so if you don't have such a transformer, you can jump the second antenna terminal to ground and use a single-fed lead in, but it'll be much noisier. No way around that -- the all-wave antenna is designed to be part of the antenna stage of the radio. You can use a random wire but you won't get all the performance designed into the set.

A radio with a single "A" screw on the other hand, was designed for a simple single-lead-in antenna with an impedance of over 1000 ohms. Coax cable is 75 ohms, so the best signal-to-noise results would still be achieved with some sort of matching transformer. Most people at the time didn't bother with such technical details, and put up with the noise -- which is why the advanced "all wave antenna kits" were so revolutionary when they were introduced. You can also find a lot of ideas for noise-reduction and signal improvement in the DX radio magazines of the time -- Radio News, All-Wave Radio, etc.

If you want to try an original all-wave antenna. they're not uncommon on eBay. A complete kit in the original box will run $30-$50 or so. There are several good brands -- RCA, Philco, Taco, Allied/Knight, etc. all put out these types of aerials and all of them operate on the same principle.

One more thing to note -- there are far more sources of household interference in 2022 than there were in 1937. Computers, DVD/Blu-Ray players, smart appliances, smart electric meters, light dimmers, and, especially, any kind of "wall wart" switching power supply will throw off all kinds of humming, buzzing, and hash, that wreaks havoc on the AM broadcast band, especially toward the lower end of the dial. If you have a serious problem with this kind of noise, no entenna will make a difference -- you'll need to go around unplugging devices until you find the source or sources.
 

2jackmans

New in Town
Messages
2
Thank you Annie for your reply. My radio has a single terminal for the antenna and a ground terminal attached to the chassis. The radio is a Philco Model 70 cathedral style built in 1930. What type or model is the transformer you are recommending? Does the long wire antenna connect to one end of the primary and the other end of the primary to ground? And the secondary one end to the radio's antenna terminal and the other end of the secondary to the radio's ground (chassis). Is the transformer mounted near the radio or near the long wire where it enters the house and a coaxial cable from there to the radio?
Keith
 

LizzieMaine

Bartender
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32,958
Location
Where The Tourists Meet The Sea
The only matching transformers for 75 ohm coax that you can get nowadays are designed to match to the 300 ohm antenna terminals on an old-style television set, so that wouldn't be much good for a radio with a single antenna terminal. With a set of this type, you're best using just a single antenna lead, soldered to the antenna wire -- which was what it's designed to use -- along with a good ground connection to a cold-water or radiator pipe, and, if the antenna is outdoors, a grounded lightning arrestor between the lead-in and the radio. This is how 99 percent of antenna hookups were done at the time your set was built, and should give reasonable results depending on how long and high your antenna is and what sort of receiving conditions exist in your area.

There were aftermarket wave-traps and similar gadgets sold at the time for this type of radio that can be useful for nulling out specific sources of interference, and those might be worth looking for if you have problems. Most of them were just simple tunable capacitor circuits inserted in series with the antenna lead, and were just hung from the antenna lead or mounted inside the cabinet. The fancier ones might sit on the table next to the radio --

vintage-decorative-du-wa-set-top_1_97ab0c7e3cac8b4be039fd834d0ace9a.jpg

Some of these gizmos worked, some of them didn't, depending on the specific conditions. You might also have good results using an AC line filter that plugs into the wall and the radio plugs into that.
 

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