[TenTec] Next on the Aragonaut 509 - output filter tuning

[MadScientist]

Well, a sweep generator, as called out in the manual, is preferred.

Lacking that. here’s a way to get around the lack of one.

This circuit is a bandpass circuit but, fortunately, only has two points of interest, rather than the 4 or more used in old TV video IF’s. One coil slug for each band peaks the high frequency end, the other peaks the low frequency end. The low Q of the circuit thus allows for a bandwidth of 500 KHz or so. This is known as stagger tuning.


1) Assuming 80 meters is OK, plot the throughput of the tuned circuit (radio power output, staying below ALC level) versus frequency, from 3.5 to 4.0. Do this in 50 KHz steps, so you will be able to see any dips in response over the range.
2) Go to 40 meters and do the same thing from 7.0 to 7.5 MHz to see where you stand at the start. You’ll probably see a single peak somewhere, which is what most people would try for, lacking knowledge of the circuit’s intent.
3) Starting at 7.0 MHz, adjust each core of T11 just a  bit, then back to original position. Identify which one makes the most difference per quarter turn at 7.0. put both back where they were.
4) Go to 7.5 MHz and do the same thing. These steps tell you which coil core tunes which end of the band.
5) Peak top and bottom alternately, adjusting the one for that end of the band only, a few times at about 7.050 and 7.450.
6) Once you reach a state at which the two adjustments are more or less peaked at their respective band ends, perform the same plot of output versus frequency as done in step 1 but on 40 meters.

This should get you pretty close. You should then be able to make fine adjustments along the entire band to get the flattest response you can.

Gary 

W0DVN

> On Feb 6, 2019, at 2:16 PM, w0ep <w0ep at w0ep.us> wrote:
> 
> 
> 80262 - Front End
> 
> It has RX filters and TX bandpass filters
> 
> In my copy of the manual it is covered on pages 3-7 and 3-8
> 
> 
> Chris
> 
> 
> 
> On 2/6/19 1:33 PM, MadScientist wrote:
>> What board number are you addressing?
>> 
>> The TX low pass board, 80260, shares one variable cap on all bands and that is for sampling to the directional coupler.
>> 
>> Gary
>> 
>>> On Feb 6, 2019, at 9:41 AM, w0ep <w0ep at w0ep.us> wrote:
>>> 
>>> 
>>> My next need for this Aragonaut 509 is tuning one of the TX output filters.
>>> The manual says not to touch them.
>>> 
>>> Ok!  I'm for that, except someone has already been there and my 7 MHz filter
>>> is blocking the signal from getting to the PA board.  How do I know?  I
>>> twiddled with it just enough to see it come up drastically.
>>> 
>>> So now I can testify for sure:  this filter needs to be adjusted.
>>> 
>>> Any ideas on how to do it?
>>> 
>>> 
>>> Chris
>>> w0ep
>>> 
>>> 
>>> 
>>> 
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