Watt Meter repair and modification advice needed

[WBear2GCR]

the meter in the Bird is well, a meter... you can outboard any suitable meter...

I have a 19" rack mounted Bird broadcast meter bridge that indicates forward and reverse (they call it something else) and has a "meter relay" on one of the two meters, with a barrier strip in the back to connect out to the remotely placed "slug" box... sorry I can't recall the model # at the moment, but I did finally find the pdf of the schematic online... I intend to put it into service... Al VTP was talking about what
he should do with his rack mounted slug box... guess that meter bridge is the right idea.

                         _-_-bear

[KL7OF]

I bumped up this old thread because I finally got around to repairing the shelf full of broken ham swap wattmeters I have acquired..I have 3 DRAKE W4..a SWAN 1500..and a MATCO PX100.
  I was able to get the Matco and 2 of the Drake W4's going with a diode or two but the biggest problem with the drakes was the trimmer pots were all dirty..a little spray and some back and forth action and the pots came to life..The third W4 has an exploded 3-8 pf tuned slug (I don't have one) on the input used for zeroing the reflected side  and I can't seem to find the problem with the Swan...The Swan shows about half values on all its scales and I can't seem to find any out of spec components...
   Since I started this thread, I have acquired 2 BIRD 43 wattmeters...Both are swap meet specials...So I decided to check all of these wattmeters today for accuracy..According to Ohms law  E= Sq root of PxR...so Sq root of 100 watts x 50 ohms =70.7 volts RMS  I set both W4 wattmeters  according to the drake manual at 100 watts using a TS520 and a HP RMS voltmeter and a Heath Cantenna  The Matco was within a couple watts and Bird #1 was reading 5 watts high with a 2500 watt slug Bird # 2 read 25 watts high with the same slug..(I know that a 2500 watt slug is not best for 100 watt range readings but its the smallest one I have right now)
  The Drake W4 wattmeters and the Swan wm 1500 can be calibrated in all their ranges..They are limited to 2KW at 2-50 Mhz..
  The Bird wattmeters cannot be adjusted or calibrated ..The slugs contain the calibration and are a  simple circuit with the pickup coil/antenna being the most critical part of the 3 active components..You get what you get ...The thruline pickup is a brass casting that looks like a kitchen faucet..They can however read from DC to Daylight at all power ranges..if you have the slugs....(expensive) and they are very rugged..
  It is nice to know the power output of your rig, but I don't feel that I have to know down to the last watt...I'm feeling good that I have 3 calibrated (albeit to my old HP 400H) and 2 others that are close.....
   I like the Drake W4 for ham use...Cheap, can be repaired and calibrated, and they are still around at festers...
  I am thinking of homebrewing a max scrote wattmeter .... WA1GFZ has suggested...the Collins circuit...I'll take a look...

[KL7OF]

Exploded 3-8 pf slug tuned cap in Drake W4 wattmeter..Made a mess but I don't think it damaged the PC board...Just blew a nice electron hole in there

[ke7trp]

None of the watt meters that where discussed are not going to take more then a couple hundred watts of AM.  You can run full legal limit but with a loss.  The torroids get hot. 

Even the so called "3kw" digital meters will be wasting power.  Run AM through one and then put your hand on the sensor.  HOT HOT HOT.  I never noticed this before but then one day, the coupler blew out. 

After talking with the manufacturer, I was told that none of them are rated for continuous use.

The larger cores are a great idea and that was suggested to me as well.  Then, when I spoke with my friend who runs SSTV at 1500 watts, He told me that even the 10KW coupler with the larger cores gets very very hot.  He said the RF heat loss is very great and as a result, None of the high power SSTV guys can use them.

The higher the SWR, The more loss of course. 

This is where the bird steps in.  RF tight, the coupler never gets warm or has any heat loss. You dont have to worry about RF in the shack or any impedance bumps in the line with some cheap wire jumper inside a box. 

If you have a small low power HAM station, Those meters are great.  But if you have a high power AM station dont bother.   For a year, I heated one of those up and did not know it.

I recently went to a dual bird setup.  A dual element line section with a dual bird watt meter cabinet with PEP kit.  This setup as a 1x a 2 x and a 5 x switch right on the front.  THis way you can use one 500 watt slug and get 500, 1000 and 2500 scales. Or a single 1000 watt slug and get 1000, 2000 and 5000 watt scales.  You also get a PEP mode which is required to make sure you are not going over the FCC' 1500 watt PEP limit.

I have a 50 watt slug in the reverse postion for tuning the antenna tuner. I can tune the tuner flat with 0 watts reflected at full power now live under key down.

No more heat loss.  Simple meters in a box with a real RF line section. Thats why this meter has been the best since the 50s.

C

[KB2WIG]

The Bird is the Word



klc

[KB5MD]

 Don't worry about how many watts, just turn up the "wick" until the house lights dim and you'll have it about right!

[KL7OF]

Clark...Thanks for telling us about your wattmeter experiences...
I ran one of the W4 Watt meters last night on my Gates BC1G on 160 meters at max AM output...After an old buzzard transmission, I was unable to detect any heating of the pickup torroid....I just spit on my finger and felt the torroid...not too scientific but it wasn't even warm...I agree that birds are the $hzit with the real RF line section..and I agree that  your rack mount PEP model is the way to go...Maybe one of those will come my way some day.....Steve

[Jim, W5JO]

I agree that birds are the $hzit with the real RF line section..and I agree that  your rack mount PEP model is the way to go...Maybe one of those will come my way some day.....Steve

Keep in mind that even the valued Bird's accuracy is no more than 5% of full scale.  I have never heard of a heating problem with any wattmeter as Clark mentioned unless you put too much power through the thing and it is not rated for that amount or maybe a very high SWR.

Some one mentioned the LP 100 by N8LP.  Typical accuracy  is 1% or less and, depending on the sampling box you get, can measure up to 10KW.  It is also very accurate for PEP and has an option for dual couplers.  It is a bit pricy compared to many hamfest Birds but the accuracy is known when you get it and you can easily adjust it.  Unlike the Bird it will read net power to the system regardless of reflected power, something the Bird won't do. 

There are some other nice features of the LP 100 that I sold my Bird 4411 to get one.  With any Bird I have ever seen requires a formula to calculate true peak mostly because of the time constant of the meter.

[KL7OF]

From the BIRD 43 operating instructions..."Caution, handle elements with care.  Calibration could be disturbed if they are dropped"
ACCURACY: 
  CW (all models) +-5% of full scale
  Peak Power (43P only) +-8% of full scale


Jim ,that  LP  100 sounds like a nice unit

[Jim, W5JO]

I bought an LP 100 several years ago and have never looked back.  Bird accuracy is good but the LP 100 is better and more accurate on peak reading.  I believe he is making a rack mount now but haven't looked in a while.  The Brid is the thing I would use for field use but for home the LP 100 is better hands down.  If you haven't looked at the specs go to his website and read the info.  If you want to spend the money for one, it would be less than a Bird with the slugs from a reputable source.  I wouldn't trust the calibration of any slug, Bird or otherwise, bought at a hamfest if you need accuracy.

When I did field work in the land mobile business I always guarded my Bird elements carefully to keep from dropping them.  If you don't have the set up and equipment to calibrate them, Bird charges a pretty penny for that service.  Of course the ones you have been repairing can be calibrated anywhere on the scale, full or half so you can use a standard to do the calibration to your liking.  That would cost a lot less but they are not linear.

[KL7OF]

As the operator of an amateur station I am  trying to get the best accuracy in my measurements that I can get with the equipment available to me..that's what most amateurs do ..It is fun bringing these older wattmeters back to life and comparing them to each other...I've learned a few things along the way as well....

[ke7trp]

Steve,  I am sitting here scratching my head on how you ran a W4 watt meter rated at 2000 watts max power with a 1kW carrier full modulated BC transmitter....

That meter is rated at a max of 2000 by drake. So either the meter is not reading correctly or the transmitter is running way down on power.  Not sure brother!  If I have my vmc rig into a dummy load in third gear,  I need a 5kw slug in the bird.

I was thinking about the torroid not getting hot at work today and it hit me. It was likely because you where on 160 meters.  On a higher Frequency, the heat might come into play.  


On 40 or 80 things might heat up,  On 20, maybe they burn down?  I dont know.  

Jim, Those LP meters are nice.   Its only as accurate as the calibration though. N8LP was nice and helpfull.  He told me about the issues with continuous RF duty with Torroid core sending watt meters.   Most of the 3k rated units will not take it and will heat up.  He recomended AGAINST AM use.

The real trouble in My case (again, Pointed out by n8lp) is that the heat over time changes the permeability of the cores.  Then, One day, Its way way out of value and the torriod starts to draw more and more current. It is placed across the antenna lead to ground (one of them is).  When you start to pull more and more current, things really really heat up.  N8LP sent me two new cores and enough wire to rewind my own cores for just $10 with postage. Not a bad deal.

The sad part for me was I did not look over at the meter when the torroid became a load.  I smelled burning and looked up to see my 4-400s GLOWING RED and my plate current way over in the corner pegged.  I let off the key but it was to late.  The 4-400s where unhappy and had to be replaced. They where vintage eimac round fin 4-400s that where new in the box. I almost cried.

When I reached back to find out what happened, the RF sensing unit Burned my hand.  It was very very hot.

N8LP told me that he uses some larger Torriods for higher power but did mention they are the same in all the RF coupler units. The only difference is the amount of winding on the core for different power take off to the meter.

I think you will be ok but it depends on the Frequency, SWR, and power you run along with time.   I ran mine for several years without any issue Jim.  

The SSTV guys just dont use them.  Even the Palstar 4KW unit with the same type of coupling unit gets smokin hot with only 500watts SSTV.  When you gotta fan cool your watt meter coupler, Its time to rethink things.

A bird runs Ice cold always..  I just dont like having a potential load inline with my transmitter.  Now for my SSB station, I love the digitals!

C

[Jim, W5JO]

I don't run 3 kw continous  Clark.  I stay just below the 1500 watt peak and haven't had a problem in the 4+ years I have owned the Instrument.   . That solves any heating problem if my sensing unit is good for 3 kw.  One must remember that all the manufacturer power ratings today are PEP not continous commercial ratings. 

It works fine up to 10 meters and I am careful to avoid either open or shorted circuits.  That helps.