I'd try putting a single steering diode from the CT junction of the input
transformer to the bias network. Just ensures safety.
Are you SURE that you have good bias? Your bias is a LOW impedance source?
I use a 5A regulator for every 8 transistors, and I don't have any biasing
issues....
What is the brand / model? If this is a CB type amplifier, letting me know
this info will allow me to 'fill you in' on the mix in the transformers.
Some will go to 40 meters. Some to 80. Some I've tested will only measure
good to 21 mhz or above. Some are coming with transistors AND ferrite
OPTIMIZED for 6 meters! If your amplifier has SD1446s in it, this could be
an issue, they are VHF xisters.
IOW, a bit more info is needed, but I'd say it's probably in your ferrite
mix... If not, then I'd check to ENSURE you have a low impedance bias
supply, that can supply .8 volts under ALL drive levels.
I run a Messenger M2000 (16X2879s) and a Texas Star Sweet Sixteen (8X2879s)
mobile..... Been here, done this :)
--Shane
KD6VXI
On Fri, Nov 19, 2010 at 6:45 AM, Dan Sawyer <dansawyer@earthlink.net> wrote:
> Ah, good question. The case is a simple single tone, x MHz in produces
> an amplified output of x MHz at plus some level and a series of odd
> harmonics, 3 times x. The 3rd harmonic is down 10 db from the original
> signal.
>
> Some additional follow up information:
>
> 1. the bias is set near the high end, increasing its value does not
> significantly add to overall gain.
> 2. I suspect an output impedance mismatch, if that were the case could
> it cause harmonics?
>
> Dan
>
> On 11/18/2010 10:39 PM, Fuqua, Bill L wrote:
> > Another question.
> > Are you saying if you put in, as an example, 10 MHz you are getting a 30
> MHz signal only 10 db down from the 10 MHz.
> > Or is this a two-tone measurement and you are looking at the
> intermodulation products?
> > And if you are how do you have your instrumentation set up?
> Sometimes there are errors produced in the instrumentation.
> > 73
> > Bill
> >
> > kind of late. I must get some sleep. Check in the morning.
> >
> > ________________________________________
> > From: amps-bounces@contesting.com [amps-bounces@contesting.com] On
> Behalf Of Dan Sawyer [dansawyer@earthlink.net]
> > Sent: Friday, November 19, 2010 12:31 AM
> > To: Amps
> > Subject: [Amps] source of '3rd harmonic'
> >
> > All,
> >
> > I am trying to add bias to a commercial class B NPN RF module. The input
> > and outputs are 4:1 and 1:4 'binocular' transformers, feedback is a
> > simple CR network. The output has a significant 3rd harmonic, about
> -10db.
> >
> > I have done research on the source of odd harmonics, however I can't
> > find specific references. What is the root cause of odd harmonics, what
> > would affect the level of harmonic?
> >
> > Thanks for your help,
> >
> > Dan
> > kb0qil
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
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