>Don't think any diodes in the circuit are linear from 160 to 10.
Diodes are not linear. But, that is not the problem. The non-linearity does
not depend upon frequency but is controlled by the rectification process.
Non-linearity can be calibrated out easily with a meter scale. The change in
levels due to frequency are caused by the frequency response of the toroid
device. Both the core material and the number of turns can be adjusted. It is
quite easy to determine what the bandwidth is by feeding the sensor with a
wideband signal generator and measuring output of the sensor versus frequency.
If adjusting the number of turns and the core does not give you the range you
need, you can make frequency dependent compensation on the output of the sensor
(for example, small value bypass caps on the output line will not charge the
diode at the lower frequency and be useful if the voltage output of the sensor
dropped off with frequency). The right combination of these three factors
should allow you to construct a sensor that covers the range you need. This
empirical approach is perfect for the amateur since it requires no math, no
knowledge of physics and very little expenditure of money. You should be able
to become an expert in this area with less than a 6 pack and one evening of
bench work.
Colin K7FM
-----Original Message-----
From: craxd <craxd1@ezwv.com>
Sent: Oct 7, 2004 11:13 AM
To: robrk@echomatrix.net, "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] Power metering in linears
Rob,
You are correct on this. Most use a 1N270 or so, but I'm not sure what
would be needed for that wide of a range.
Will Matney
robrk@echomatrix.net wrote:
>Don't think any diodes in the circuit are linear from 160 to 10.
>
>
>
>>Tom,
>>
>>Stripline type RF sensors are narrow-banded and generally won't work
>>with that type of band spread. The toroidal transformer should work if
>>the core is rated for the complete frequency range like 3-30 MHz. If
>>not, you may have to add a switch to kick in another potentiometer just
>>for 80 meters and maybe 160 meters. To get the meter to null is another
>>thing and has to be done to read forward and reflected power. You may
>>just try different toroids first before doing any modifications.
>>
>>Will Matney
>>
>>
>>Hello technicians,
>>
>>I was adding a power meter to a new homemade linear. I used the
>>directional coupler of the "Digital PEP Wattmeter and SWR calculator" from
>>an old ARRL handbook (1987). I did not get a too deep null on calibrating,
>>so the directivity was only 20 dB. As I only wanted to monitor the output
>>of a linear with that coupler, the directivity was sufficient.
>>
>>The problem: The output voltage for a given power is the same from 40-10m,
>>but nearly null on 80m and different on 160m.
>>
>>Then I tried the design from the linears in the W6SAI handbook. They use
>>Amidon 50-6 toroids. The output voltage ón 160 is about 1/2 of the voltage
>>on 10m.
>>
>>Has anyone successfully built a directional coupler with constant
>>frequency behaviour from 160-10m?
>>
>>I would like to have proven designs.
>>
>>Thanks!
>>
>>Tom, DJ5RE
>>
>>
>>_______________________________________________
>>Amps mailing list
>>Amps@contesting.com
>>http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
>
>
>__________ NOD32 1.880 (20040928) Information __________
>
>This message was checked by NOD32 antivirus system.
>http://www.nod32.com
>
>
>
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|