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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 2nd Sep 2019, 9:06 pm   #1
nikos111
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Default Koden KS-357 Direction Finder.

Restoration work
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Old 2nd Sep 2019, 9:08 pm   #2
nikos111
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Default Re: Koden KS-357 Direction Finder.

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Old 3rd Sep 2019, 5:42 am   #3
batterymaker1
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Default Re: Koden KS-357 Direction Finder.

I imagine that thing's sensitivity will be hotter than a firecracker once restored.
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Old 3rd Sep 2019, 8:04 am   #4
Nickthedentist
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Default Re: Koden KS-357 Direction Finder.

Hello Nikos,

For those of us who don't know much about the equipment you're restoring, could you tell us a bit about what it does and how it works, please?

Nick.
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Old 3rd Sep 2019, 8:35 am   #5
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Default Re: Koden KS-357 Direction Finder.

It's a nice little transistor radio with RF stages and what looks like several IF stages (hence Batterymaker's comment)

The big lump of a handle houses a ferrite rod antenna, connected straight down through the pivot axle to the variable capacitor below. There is a signal strength meter in the top plate.

Rotate the antenna to find a null and read the angle from the scale.

The problem is that there are two nulls if done simply. However, the little whip antenna receives a bit of (mostly) the E-field of the incoming signal, and adding its contribution to the ferrite rod makes the two nulls unequal, so there is only one good null and the ambiguity is resolved.

The scale is only good, of course, if the orientation of the box is controlled with respect to your boat.

Tuning range will be long, medium, probably the LF aviation beacons, and maybe the lower marine band.

It should work as a basic marine band RX with the adventage that you can take a bearing on the transmitter.... very handy if you hear a call for help.

Electronically, it looks pretty good. But from a point of surviving on, say, a yacht, the weatherproofing is non existant. It needs to be kept in a protected place.

If it's been restored, it looks almost like new.

David
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Old 3rd Sep 2019, 9:00 am   #6
turretslug
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Default Re: Koden KS-357 Direction Finder.

It is a nice radio, a good example of an interesting if somewhat niche type of receiver. The compactness and very low power requirement of transistors meant that what used to be called a "radio compass" (descriptive if quaint term) changed from an expensive, bulky and specialist fitment to something that was affordable and available to Joe Public for the likes of modest yachts. I'm willing to bet that it would run for a long time on even a cheap primary battery, again meaning that it makes sense to use on small pleasure craft, or available for use under circumstances of stress like power/generator failure.

There are innumerable tales, some tragic, of the ambiguity associated with radio DF'ing on a loop (going as far back as Amelia Earhart and probably earlier), so the whip resolving was an important part of the radio compass principle and adds an interesting technical aspect to the set.

If nothing else, this should make a good LF/MF DXing set, and it looks as though there are quite a few IF cans for good selectivity. Could the signal strength meter have been replaced at some point? I like the output stage heatsink- looks like a classic bit of pragmatic and down-to-earth Japanese production engineering.
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Old 3rd Sep 2019, 2:24 pm   #7
nikos111
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Default Re: Koden KS-357 Direction Finder.

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Old 3rd Sep 2019, 2:40 pm   #8
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Default Re: Koden KS-357 Direction Finder.

Image 4 in the above post is from an upmarket version of the same type of equipment: https://www.revolvy.com/page/Bendix-...9EmDQvA7E&cr=1
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