[TenTec] Ten Tec Centaur 411 10m Mod Needed
Rick - DJ0IP / NJ0IP
Rick at DJ0IP.de
Fri Feb 14 02:36:47 EST 2014
Though Brian is correct, it is still bad practice to do this because it does
cause additional distortion in your signal.
If you use an input filter rather than just direct coupling (with or without
a swamping resistor), it improves linearity about 10dB. This means your
signal will be broader on the band than it would be if the linear were wired
Although many of the first amplifiers did that when the first SSB linear
amplifiers came out, we quickly began adding input filters to our
amplifiers. There is always a cost for cutting corners!
BTW, at first I also made the same assumption Jim made.
I thought he removed the output filter which would be the case for a
Silly me; I forgot that the output side (here) is a Pi network and all you
have is taps to the coil.
Jim, we're getting' old!
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Brian
Sent: Friday, February 14, 2014 5:13 AM
To: Discussion of Ten-Tec Equipment
Cc: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Ten Tec Centaur 411 10m Mod Needed
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>
> 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.
> 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
>> Perry w8au
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