Re: Very low power output (BitX40), everything appears to be working but setup driving me crazy!

John McFadden <johnamcf@...>


What frequency did you test on, and did you try other frequencies?

It turns out my Bitx40 shows different output levels depending on the frequency across the 40m band, maybe your board has the same issue.

I emailed out graphs of my board's output under the heading "Power output decreases as a function of frequency? #bitx40" with one today.


On 12/30/2017 9:21 PM, Gene Nitschke wrote:

Hi Jerry,

Sorry for the delay (holidays you know).  

I do have a number of the 100N50 resistors and find that they work great.

Yes, I saw the notes from Jack but I am unclear about the operation.  Software apparently is in his book and likely available in QST sometime in 2018.  

Can I just use the circuit w/o the nano, I assume the resistor divider is for sampling by the nano?  If I connect the rig across the 50 ohm load and measure the voltage across the capacitor, what is the relationship of voltage to power (is it simply V^2/R)?

From: <> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Tuesday, December 26, 2017 11:39 PM
Subject: Re: [BITX20] Very low power output (BitX40), everything appears to be working but setup driving me crazy!
How reasonable do you want to be on the cost thing for your wattmeter?

Could build a dummy load with wattmeter along the lines of the one Jack described, reads peak power:
In post 37017 Mike describes using these $0.10 resistors:
So you need a 50 ohm load resistor of some sort plus a diode (a 1n4148 or 1n914 would do) plus 2 resistors and a cap. 
Use your DVM to measure the voltage from the cap.  Total cost is around $1 from Mouser, plus $10 shipping.

Some really nice 50 ohm RF loads on ebay, need an awful big heatsink if giving it 250W
I've got some of these on order, should show up in a month or so.
1Pc x Load Resistance RFP 250-50 250W 50 Ohm 250N50 TC RF Resistors. High-frequency high-frequency dummy load 250w 50 Ohm. 3, Silver microstrip pin as much as possible with the input signal parallel. | eBay!

Alternately, no dummy load but include an inline SWR meter for daily use with the rig:
No, it's not meant to be left in line, as it sucks up all the power and is not a "sampling" wattmeter. Peter Parker had a really simple sampling as a tuning indicator ...

Cheapest solution:
Stick with the CB wattmeter, but ask local hams to check it against some better instruments.
It's probably just fine for what you are doing.

 Jerry, KE7ER

On Tue, Dec 26, 2017 at 07:53 pm, Gene Nitschke wrote:
Is there a good (reasonable cost) watt meter that would be better to use in these situations?

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