Some History of Dosy Wattmeters

[NorthStar34]

Emil copied the Black Cat meters. Devon at

Dosy called them to ask how to deal with a specific problem that they were having. Kenny told him a BIG lie. They have never been able to get the meters to work as good as the Black Cat's were.




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[nomadradio]

Hmmm. Don't know any of the individuals mentioned, but the wattmeter designs are not at all similar.

Black Cat copped out and used a "narrow-band" design that would only stay calibrated over a narrow range of frequencies. It's a "RF Voltmeter" circuit with the scale calibrated in Watts. Pretty accurate into a dummy load or other low (1.1) SWR. Soon as you change frequency by more than a MegaHertz or so, the calibration goes out the window.

One of my favorite demos 25 years ago was to take a 3-Watt 2-meter ham HT and patch it into a Black Cat wattmeter, driving the dummy load. Because the Black Cat used a capacitor tapped off the coax center-wire, it was roughly 100 times more sensitive on 146 MHz as it was on 27 MHz. Sure got some suprised looks from the CB operators when my battery-powered HT showed 300 or 400 Watts on the Black Cat meter. I would assure them that it was a "false" reading, and not to be trusted.

The Dosy meters mostly used a current probe design, with the coax center wire passed through a toroid coil. Not too different from the Drake and Heathkit wattmeters, but modified to "sorta" read peaks. The higher the power range you select, the closer it will come to reading actual "PEP" power. On the lowest range, peak readings will tend to be a bit stingier. It's a trait shared by nearly all other "passive" peak-reading RF Wattmeters.

73

 

[Geekster]

I remember a few years (decade) ago we compared the Dosy/Black Cat to the PDC on our test bench. I liked the Dosy meter but I wasn't allowed to comment as such due to the conflict of interest.

I would like to find another Dosy one of these days. I find their website doesn't offer much on specs. I also found the same for Para Dynamics. However I am resolving that problem on my website. I always performed the insertion loss of each product so they could list it in the catalogs back then. I like the available manuals on the Dosy website. I am working my way down the manual and schematic list for PDC.

If I remember correctly the Dosy (and PDC) fell off dramatically in RF readings after the 12 meters band. We calibrated in the center of 11 meters.

Off topic...

But I seriously doubt Omnitronics will bring back the older PDC lineup. After Astatic bought out PDC in the late 90's (just before I had left with Paul to form Palstar) they immediately dumped the offshore lines. I am not sure if it was due to them not wanting to deal with Sam Woo and Euro-CB but I feel that most of the sales where within those lines. They only kept the PDC 600/700 lines.

I see they have incorportated the 5000 watt scale into one meter which is actually a better idea. The older PDC meters were assembled in Ohio -- however from what I have heard they are now assembled in Mexico. I guess that is enough of PDC history for now.

Sorry didn't mean to hi-jack your topic.

Do you think Dosy will ever update their website?

 

[Geekster]

Sounds good to me... I prefer the Bird or HP lineup but Dosy has been a good choice.

1stop I have heard that name before somewheres...



PDC has been around since the '70's before Valor purchased the company. I am still searching for older pictures of PDC equipment. I have quite a few thus far.