Thursday, March 15, 2012

Needing a SWR POWER meter for 70MHz



This SWR measuring device was resting in my junk-box for many many years.
To complete my 70MHz XVTR with an internal SWR / Power meter I was planning to build a simple one. Then I remembered this very rugged device with two N-type connectors  unknown freq range.

My Daiwa NS-660P cross needle supports remote sensor / SWR head over the DIN connector at the back.  Peak hold with external 9Vbattery or power adapter.
High quality device  3 range 15 150 1500 
It even worked at 500kHz.

So I could connect it straight to the NS660  and could compare the readings  At 100W level almost same at lower levels the Daiwa is more sensitive.

The junk-box type  uses a toroid current pick up  and 2 capacitive  Voltage coupling.

But reversing the bridge in-line did not reverse the reading. I was expecting to see the same power level as reflected but  it showed some reading at both needles.
One N-port is marked  "to ant."  clearly.  
The diodes look like Germanium point contact types. 
At 70MHz good reading  but no reflected power.. My antenna just has no reflected power at  al 3 VHF bands!  hard to believe but its a fact.

Both diodes are tested good  the coil seems to be okay although I did not open the square box where this toroid must be in..

Is this type of SWR meter circuit reversible or not I am not certain.
I guess the Daiwa uses the same circuit  and not the directional coupler type of circuit used in the simple type of 27MHz SWR meters that is reversible.

Just reversed the NS-660P in the line and the reflective meter now gives the forward reading.
That means the remote sensor must have an error.
Have to check it more deeply now.

Anyway I will have to make a smaller SWR sensor to integrate in the XVTR.
But It would be nice to have an extra remote SWR sensor of good quality
I will Google some more  for  this type SWR  and its properties. 


 


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