There are a number of after market peak/rms meter boards sold for the Bird 43 and other popular watt meters.
Electronic circuits can easily be adapted to scale the meter movement to X2, X5 & X10 values in both the original rms & peak reading functions. T'was what I did before I stopped using the Bird meters in lieu of the simplicity of the Telewave units. Over time I realized I mostly only needed an inline relative figure for both forward and reflected power values as long the ratios are correct. cheers, skipp > "Gary Schafer" <[EMAIL PROTECTED]> wrote: > > The calibration won't be good for that element either. The 43 meter is 30 > microamps full scale and has a resistance of 1400 ohms (if I remember > correctly). If you put a resistor across the meter or in series with the > meter that changes the part of the curve that the diode detector in the > element works on as more or less current has to flow in the diode from the > original calibration to the meter scale. The linearity will change. > > The only way to accurately change or add a scale to the wattmeter is to > change the coupling in the element. This lets the diode work on the same > curve as the meter scale is set up for. > > If you will notice, the bird meter scale is not linear and it is not log > either. There is no direct correlation between meter current and any kind of > linear or log scale. It is a non linear scale that corresponds to the curve > of the diode in the element and that curve is dependent upon a fixed load > that the meter movement provides. > > All elements have their coupling (rf) adjusted so they work in exactly the > same part of the diode curve. Meaning that a 5 watt element works on the > same curve as a 500 watt element. If it did not then the meter scale would > not track from element to element. For the diode in one element to work on > the same curve as the next the load current must be constant (same 1400 ohm > load resistor, the meter movement) and the coupling to the rf adjusted to > produce that same current. The pot in the element varies the resistance a > slight amount for final calibration but contributes to inaccuracies. > > Not that the scale on switchable power meters such as the telawave or the > bird 44** type have a scale that is much different than that of a 43. Those > meters switch in series pots for different ranges but each range is > different. > > By the way if you want to check the meter movement in your bird 43 use about > a half meg pot and a 12 volt power supply and feed directly to the meter > with a good digital current meter in series. Adjust for exactly 30 microamps > on the digital meter and the bird should read exactly full scale. Beware > that all digital meters are not exactly right either. A good bench type > fluke or hp will be best to use. > > 73 > Gary K4FMX > > > -----Original Message----- > > From: [email protected] [mailto:Repeater- > > [EMAIL PROTECTED] On Behalf Of Bob M. > > Sent: Tuesday, August 14, 2007 8:25 AM > > To: [email protected] > > Subject: Re: Re: [Repeater-Builder] Bird Wattmeter X2/X5 Range Switch > > > > The QST article achieves the X2/X5 scales by putting > > resistance ACROSS the 30uA meter. This is fine if your > > meter is reading too high, but it won't help if the > > meter is reading too low. And, of course, the > > calibration would only be good for the particular > > element you're running at the time. When you put in a > > different element, the calibration could change. Best > > thing to do if you really need accuracy is to remove > > the nameplate from the element and tweak the pot > > inside, using another known accurate power indicator > > and source. > > > > Bob M. > > ====== > > --- Ron Wright <[EMAIL PROTECTED]> wrote: > > > > > At 5% accuracy the Bird 43 aint all that accurate, > > > but has been the industry standard. But for 2-way > > > work which is long way from high tech it is good > > > enough. > > > > > > The QST mod article is good and does allow for some > > > calibration since adjustable. They simple put pots > > > in line and adjust for whatever power level one > > > wants. Bird does same with fixed resistors, but > > > wants you to buy slugs. > > > > > > 73, ron, n9ee/r > > > > > > >From: Doug Bade <[EMAIL PROTECTED]> > > > >Date: 2007/08/13 Mon PM 12:49:00 CDT > > > >To: [email protected] > > > >Subject: Re: [Repeater-Builder] Bird Wattmeter > > > X2/X5 Range Switch > > > > > > > > > > >I have a Bird 4410A which has a range selector > > > switch ( rotary) but > > > >have never seen a modified 43... maybe an amateur > > > mod??? Calibration > > > >certification would seem to go out the window... > > > > > > > >Doug > > > >KD8B > > > > > > > >At 01:17 PM 8/13/2007, you wrote: > > > > > > > >>There's a modification to the good old Bird 43 > > > >>wattmeter that adds an X2/X5 switch. I suspect > > > this > > > >>just shunts the meter movement with pots. One > > > person > > > >>was selling such a meter on eBay and claims the > > > mod > > > >>was seen in a magazine. > > > >> > > > >>Anyone seen this mod, or know where it was > > > printed? > > > >> > > > >>Thanks. > > > >> > > > >>Bob M.
