[Milsurplus] LO radiation

[Bob Camp]

Hi

Ok, just looking at 500KHz for a bit let's see what comes out of the 
numbers.

A wavelength at 500KHz is 600 meters. At 100 wavelengths you are well 
over the horizon, even from something pretty tall. On the same basis as 
before 100 wavelengths gives you a path loss of around 60 db.

Neither the RX or TX antenna will be anything other than short at this 
frequency. However if you are running a tuned loop you still can get a 
reasonable antenna gain.

 From what I have seen written about radio setups on merchant shipping 
during WW2 they ran a pretty rag tag bunch of gear. This seems to have 
been especially true of stuff like 500KC monitoring receivers. I 
certainly have seen descriptions of liberty ships running straight 
diode detectors in their 500KC alarm receivers.

So, here's a few guesses:

TX antenna loss 20 db
RX antenna loss 20 db
TX isolation 10 db

That's fifty db worse than the previous numbers. The path loss at 60 KM 
is 60 db less than the previous numbers. It still sounds like you could 
get a bearing out to 20 miles or so.

	Take Care!

		Bob Camp
		KB8TQ


On Mar 27, 2005, at 5:44 PM, Hue Miller wrote:

> However, we are not talking about a diode mixer or a regen in the 
> simple
> detector + audio circuit.  The latter were quickly replaced near the 
> start
> of WW2. Also, i assume we are considering mainly  or only 500 kHz.
> If that is true, the ship antenna was (probably? ) a short reactive 
> antenna.
> I am thinking, and i believe it can be shown, that the receiver match 
> to the
> antenna was not a good one in terms of favoring power transfer.
> I am saying, between the RF stage and the unfavorable receiver match
> to the antenna, there is not enuff signal to worry about past the radio
> room, or maybe the radio room in  a convoy vessel a few hundred yards
> away.
> I would also guess that the actual radiation varied by frequency and
> was less at 500 kHz than at say, low HF.
> -Hue Miller
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