[DSP-10] Brickette QRO QRV at n5bf/6

[Perry Ogletree]

Hint... When winding toroid cores, each time the wire passes through the 
center is a "turn", one turn would be a simple "horseshoe" of wire, two 
turns would be a single loop, etc.

73 de Perry - K4PWO

----- Original Message ----- 
From: "Courtney Duncan" <cbduncan at earthlink.net>
To: "kd7ts" <kd7ts at ispwest.com>
Cc: "Discussion of DSP-10 2-meter transceiver" <dsp-10 at mailman.qth.net>
Sent: Saturday, July 02, 2005 6:38 PM
Subject: Re: [DSP-10] Brickette QRO QRV at n5bf/6


> Yes, I have a copy of the QST article, in fact, a color one that I printed 
> from arrl.org.  Higher resolution pictures!
>
>
> kd7ts wrote:
>
>> Confirm the winding of L4 and L5.
>
> This is a little confuing.  Figure 1 says 5 turns on a T-25-17, but in 
> Figure 2 it looks like four turns to me.  I have tried both what looks to 
> me like four turns and five turns.
>
> Originally I built it with what looks to me like 5 turns on l2, l3, l4, 
> and L5.  To get it working with the SWR light out, I removed one turn from 
> each.  At that point I had inductors that matched Figure 2 and 5.1 watts 
> out forward.
>
>>
>> If these are wrong, spreading or compressing their turns has very
>> little affect on tuning.
>>
>
> In that configuration, spreading or compressing L4 or L5 had little 
> effect.  Today I took them out and rewound them with what looks to me like 
> 5 turns again.  Now I can get some roll off by compressing the turns.  If 
> I push them all up together, it drops under three watts.  I think this is 
> the right behavior.  Increasing the inductance like that should lower the 
> cutoff frequency of the low pass filter.  I spread them out to where I'm 
> getting 4.9 watts forward again.  On the schematic it looks like L2 should 
> be involved in low pass filtering also, so I took it out and rewound it 
> too to what looks like to me is five turns.
>
> With this I can get reduced power by compressing L2 also and so spread it 
> out to where it does 4.9 watts forward again.
>
> Since this is a low pass filter and since I possibly had inductors too 
> small, it is possible that the difference between 4.9 and 5.1 watts 
> forward on the Bird wattmeter to a 50 ohm resistive dummy load is power in 
> a harmonic that is now adequately suppressed.  I don't have any way here 
> to measure for this hypothesis but, thinking this, I think I'll leave it 
> this way.
>
> I cannot see how L3 is involved with anything but turning the RF and SWR 
> lights on so I left it as it was, at what looks to me like 4 turns.  It 
> had to be retuned to re-extinguish the SWR light and now I'm getting 
> expected RF and SWR light behavior again.  Is there some reason why L2 and 
> L3 have to be the same value?  I simply couldn't get reflected power to 
> null with L3 at what looks to me like 5 turns.
>
>> If the peak power (forward) is well defined by changing the spacing,
>> they are correct.
>>
>
> The peak should be broad, right?  I'm getting a peak at about the widest 
> spacings on L4 and L5 (and L2) and can certainly reduce power by 
> compressing turns now.
>
>> check the pins of the T/R relay for connection and solder bridges.
>
> Done.  Nothing anomalous found.
>
>>
>> confirm the input and output coax shields are connected at both ends.
>>
>
> I originally used a good piece of some scrap RG-58 for this which was big, 
> ugly, hard to bend, and could have been a problem.  I've replaced all 
> three RF connector jumpers (Drive, Rx, Ant) with nice miniature coax.  The 
> ends are all pretty and well made.  There is no change in max output.
>
>> Do you have a copy of the original QST article ?
>>
>> 73 KD7TS
>>
>> Mike
>>
>>
>>
>
> So, with all this, I still think I just have an underperforming module. 
> The only other thing I can think of is inadequate DC but I don't time 
> right now to try to get above the 12.4 V (after connector drops and things 
> from a 13.8 V regulated supply) that I currently have, when at max out 
> (13.6 Rx, and I think I could rewire the power to get like 13.0 at max 
> out).
>
> The low pass filter is supposed to be a matched low pass filter, not 
> particularly a matching network, right?  Everything should be 50 ohms end 
> to end and the low pass filter is just designed to be that way but not to 
> deal with any mismatch.  Yes?
>
> Oh, on the matching network L1 and C4, I do see a few percent change when 
> I bend L1 around.  I have it peaked right now too.
>
> Thanks again Mike for the consultation.  This isn't where I can't live 
> with it operationally, but the mystery is part of the fun and if there is 
> something grossly wrong I'd like to understand and fix it.
>
> Courtney
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