[Milsurplus] LO radiation

[Bob Camp]

Hi

Well I guess I just proved a basic law of physics - never try to type 
an email while being called to Easter dinner.

Obviously the path loss was 80 db before. A 60 db path loss makes sense 
if we only changed the frequency 10:1 (20 log 10)

If you have more than about 10 db of mismatch loss on each end then you 
are in trouble.

	Take Care!
	
		Bob Camp
		KB8TQ



On Mar 27, 2005, at 6:22 PM, Bob Camp wrote:

> 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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