[TenTec] Ten Tec Centaur 411 10m Mod Needed

[Brian Carling]

The absence of a low pass filter on the input stage of a linear amplifier doesn't always mean that you will automatically have unacceptable harmonics.

Radio amateurs have use linear amplifiers for years with a 50 ohm or 200 ohm swamping resistor on the input at the cathode of the amplifier whether then a low pass tuned filter.

You may very well be right there, depending on the design of the amplifier. I have not looked at the circuit all taken a measurements.

Best regards - Bry Carling



> On Feb 13, 2014, at 9:44 PM, "Bob McGraw - K4TAX" <RMcGraw at Blomand.net> wrote:
> 
> The filter is a Low Pass filter with a nominal cut-off at about 23 MHz or slightly above 15M.  As designed this prevents operation above this frequency being on the 12/10M  bands.  This filter also provides attenuation of harmonics above the designed cut-off frequency.  Now with the 12/10M filter installed the cut-off is raised to about 32 MHz thus allowing operation on 12/10M and yet  still providing adequate attenuation of harmonics above that frequency.
> 
> Removing the filter and replacing it with a jumper will allow the amp to work on 12/10M but WILL NOT provide ANY harmonic attenuation.   Any harmonics, i.e. 2nd, 3rd, 4th,  could fall into one of the Public Service bands.  Should interference occur and the user complain to the FCC, a written explanation by the operator will be required.  Frankly, in this case, I can't think of an explanation that would be acceptable.  Just remember, it is your amp and your license.
> 
> 73
> Bob, K4TAX
> 
> 
> ----- Original Message ----- From: <w8au at sssnet.com>
> To: <tentec at contesting.com>
> Sent: Thursday, February 13, 2014 8:06 PM
> Subject: Re: [TenTec] Ten Tec Centaur 411 10m Mod Needed
> 
> 
>> At 02:48 PM 2/13/2014, Kris Merschrod wrote:
>>> I did the mod from the schematic and parts that T-T sent on a perfboard - it really isn't much, but, before hand,  I pulled the 15 meter filter and put in a jumper wire - it worked like a charm w/o the filter - I am not sure what the harmonics on that looked like - others can do the hi-tech work :>)
>> 
>> Ooops... there goes the FCC type approval.. ;-)  (hope your antenna was selective)
>> 
>> Perry   w8au
>> 
>> 
>> 
>> 
>> 
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