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   Home   Help Search  
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Author Topic: SWR Meter... Need Help!!  (Read 4780 times)

Posts: 2

« on: March 07, 2003, 08:24:00 PM »

I just purchased a DAIWA SWR \ Power meter (model CN101L)- it is a cross needle type.  The instructions are pretty poor but here is how I understand this meter to operate:

Set the appropriate power 15, 150 or 1500 watts.

Select either AVG or PEP....

AVG is only for FM??
PEP is only for SSB??

Notice these are questions because this is how I read the manual but I am not sure if this is correct.

I am using this to tune a 10M dipole and here is what I have seen....

With the meter selector set to AVG and the Rig in FM mode(when I key and identify) I get what appear to be appropriate readings and I have been able to make the reading better (lower SWR) by tunning the dipoles.

With the meter selector set to PEP and the Rig in LSB \ USB mode (when I key and identify) I get nothing.  The needles do not move.

Here are my questions...
Have I got this whole AVE for FM and PEP for SSB thing right?  I had assumed that I would get a reading using any mode.

Is it pretty standard that SWR meters only work in the FM mode or unique to this meter?

What are the potential implications of no needle movement with the SSB modes?

Finally, what is the difference between AVE and PEP?

Would really appreciate some feedback!!


Posts: 21764

« Reply #1 on: March 11, 2003, 12:33:01 PM »

Whether there's actually a difference between AVERAGE and PEP power depends on the transmission mode used.

If your Daiwa meter doesn't register anything at all in the PEP position, I suspect one of two things:

1.  It is a "powered" meter, requiring connection to an external DC power source in order to work in the PEP mode.  (Does it have a DC power socket on it?  Possibly one labeled "12Vdc in" or something?  If so, you need an external power supply or the PEP function will be "dead.")

2.  Or, there's simply something wrong with it (defective).

A "true PEP" meter MUST have a source of DC power applied to it, as active, powered circuitry is required to make a true PEP power measurement and that power cannot be taken from the RF applied.  A battery, or a power supply must be used.

On FM, AVE and PEP are identical.

On AM, PEP is normally 4x AVE carrier power level, for 100% modulation.  

On RTTY, AVE and PEP are identical.

On CW, PEP is the only thing that counts, and AVErage power will vary depending upon what you're sending.  If you send a long string of "di-dahs" (like the letter "A") with no pause between the letters, e.g., didahdidahdidahdidahdidahdidah, etc, the AVErage power output should be about 50% of the PEP.

On SSB, there theoretically isn't any AVErage power because if you stop talking, the power output drops to zero.  So, the AVErage power while taking a pause is zero.  On the other hand, if you continuously speak, and speak quickly, there will be some AVErage power indicated, usually about 25% of the PEP power.

PEP = peak envelope power.   Commonly expressed as the ratio of the square of the peak RF voltage across a 50 Ohm load.  For example, if you measure 100Vpk across a 50 Ohm dummy load, the PEP power that represents is 200 Watts [(100*100)/50 = 200].


Posts: 67

« Reply #2 on: April 18, 2003, 10:17:31 AM »

Tune with CW or RTTY.

Or if you need to use SSB, play an audio tone in.

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