[R-390] Still wondering about the 100mV detector test

[Mark Huss]

As they like to say in Boston, ‘You can’t get there from here. You have 
to go to Ayer first.’*

First the DC voltage on the Diode Load is a function of the RF Carrier 
Strength (Signal Strength).

What is shown on the Line Output meter, and a meter on the Line Out or 
Speaker Out is a function of the Modulation. To prove this, inject the 
150uV, 455 kHz, 30% mod at 1000 or 400 Hz into the IF deck. Monitor 
Diode Load Voltage and adjust Line Level Gain for a reading on the Line 
Level Meter. Turn off the Modulation. Diode Load voltage will change 
little, if at all. The Line Level Meter will drop to zero.

In other words, the Line Level Meter is handy for peaking a signal, it 
being more sensitive than the Carrier Level Meter. But it does not 
relate well to the actual uV of the signal entering the RF Deck, as it 
varies with modulation.

The Line meter reads dbV at the Line Output of the receiver. The 
standard is 0dBV = 0.707 VRMS into a 600 ohm load. This would come out 
to 0.833mW. (.707*.707 / 600).

* Boston has two train stations, North Station and South Station. They 
are 1 mile apart and have NEVER HAD a direct connection!. To 
interconnect by train you used to have to travel by train to Ayer MA, 30 
miles away! The Subway, of course is easier (course you can’t really 
haul your luggage around on it), but even then you have to change 
subways at Park Street Station from the Green Line to the Red Line! Thus 
the old saying ‘You can’t get to South Station from here. You have to go 
to Ayer first!’



n4buq at knology.net wrote:

>Roger,
>
>I'm not looking at the radio right now so can't check things, but I'm 
>wondering about something.  With the line meter switch set to +10, the 2UV 
>reading translates to 12UV.  Does 12UV correspond to 26dB (400mW)?
>
>I've looked for a way to convert these and haven't found exactly what I'm 
>looking for.  A 1000cps signal into 600 ohms at 1mW should show 0UV, but I 
>don't know how to translate 12UV into dB.
>
>As I say, with 150uV modulated into the IF deck and -7V at the diode load, 
>I get 2UV with the switch set to +10; however, I only see about 15mW on the 
>TS585.  Since the line meter and it's associated hardware are all wired in 
>the main harness, the problem would most likely not be in the AF deck.  I 
>assume I probably have something going on with the resistor network on the 
>terminal board where the line out is located but not sure about that.
>
>Any input on this?
>
>Thanks,
>
>Barry
>

>On Mon, 25 Sep 2006 19:05:46 EDT, Flowertime01 at wmconnect.com wrote :
>
>  
>
>>Barry,
>>
>>The real old test from the TM is as follows.
>>
>>Line gain to max
>>Local gain to max
>>RF gain to max
>>Mode to MGC
>>Bandwidth to 2KC
>>BFO off
>>Line meter to +10
>>
>>
>>Hang a DC voltmeter on the diode load.
>>Hand a TS585 on the line output. 
>>(AC volt meter with DB scale and 600 ohm resistor)
>>Inject about 150 micro volts of 455 with 30% modulation into the IF deck.
>>Set the gain adjust or the signal generator for - 7volts on the Diode 
>>    
>>
>load.
>  
>
>>Read at least 400 milliwatt or +26 DB on the audio output.
>>This should be +2 VU on the line meter scale.
>>
>>A good receiver will get you 500 milliwatt.
>>
>>This is a go no go test.
>>
>>You either got -7 volts and at least  .4 watt out or you have an audio 
>>    
>>
>deck 
>  
>
>>problem between the diode load and the point you are measuring (line out 
>>    
>>
>or 
>  
>
>>local out on the terminal board).
>>
>>150 UV at 455 should get you an easy -10 volts on the diode load or you 
>>    
>>
>have 
>  
>
>>an IF deck problem before the diode load. IF deck problems manifist more 
>>    
>>
>as 
>  
>
>>not making signal to noise ratio than not having enough gain. 
>>
>>If both line and local fail its the common stuff. If only one audio 
>>    
>>
>channel 
>  
>
>>fails its in that channel.
>>
>>All the other test are just to help narrow problems down.
>>
>>Any thing you read any where between the original TM and an Email today 
>>    
>>
>is 
>  
>
>>subject to the same disclaimer. Errors in print do happen.
>>
>>Do the test and put you anxiety to rest.
>>
>>Your off looking at these point that change with every tube.
>>Pick a point near a tube. Swap at least three tubes into the circuit and 
>>measure the same point with no change except to swap the tube. Wait for 
>>    
>>
>the tube 
>  
>
>>to warm up and settle down. Take a reading. If you get two tubes that 
>>    
>>
>give you 
>  
>
>>the same meter reading you are lucky. 
>>
>>Roger AI4NI
>>    
>>
>
>
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