[600MRG] Transformer design

[K9FD]

Why waste time, money and RF..  if your using a variometer from the 
antenna to ground,
just tap up the variometer coil a few turns from the bottom and bingo 
you have 50 ohm
match.  nothing else needed.

K9FD
>
> Winding toroid transformers is the main bang around here this week, 
> Paul...
>
> _2.4" #77 mix_ works FB here OM... ( 630m )  Like Palomar..
>
> _Ratio of turns_ is your main scope.. This 630m QRO cube is a pair of 
> hexfets with 40V @ over 10 amps available..
> It was a Mitsubishi AD7 audio amp., since which time has been many 
> different RFPA's here
> Just one pair of hexfets in push pull with some parasitic suppression 
> in each drain.. No source resistors..
> 40Volts / 2.8A =  14 ohms Z on the primary... It's more like 11 ohms, 
> not too critical on broadband device...
>
> 14 ohms to 50 ohms Z is 3.6 turns ratio...
>
> Decide early how fine you want to make your transformer tune.. 500 
> ohms worth of inductive reactance is good minimum then you have enuf 
> turns to tune both sides of 475 kc. with..
> With 4 turns on the primary, center tapped for the B+ you can start 
> with 15 turns on the 50 ohm output side interweaved with primary..
> When you hook it up to the load you can look with SWR meter then add 
> or subtract one turn of wire at a time from the secondary winding and 
> measure it again...
> Bull's eye is 50 ohms for secondary...
> Why extra hardware RF switches to go wrong?? This is a project for 
> learning and actual use, not a production model, yet...
>
> Ain't too many RF people left...
>
> First it was the 2.4" #77 core for the litz loop direct to transmit 
> converter, that's about 30 ohms run up to 50..... Then build proper 
> 2.4# #77 core for  the hexfet PA outputs...
>
> This is enuf for a while, we all can chew it up here till it comes out 
> all fine in the mind...
> Think about adding and subtracting secondary turns like sewing until 
> tuned, dress, tyrap, spit shine and go on...
>
> It was a day like that around here.. After the antenna transformer and 
> PA final toroid tank, I then had to look in to the RFPA antenna port 
> to see that it also appeared as 50 ohms as well, else goofy sparks and 
> unexplained mini lightning and now it looks like the parasitics are in 
> synclocked in phase and adding to the overall efficiency...
> Real clean @ the antenna input now... 50 db down @ 120 cycles...
>
> Used this poor man's Junk Box jewel to see litz loop Z ending up as 50 
> ohms R...
>
> You can see a lot with an old SDR-iq receiver, a simple signal 
> generator, and a swr bridge, nothing fancy just for S11 measurements, 
> this is the litz loop..
>
> http://www.radiocom.net/600M/VNAsetup.jpg
>
> Only seem to need 47 watts to the loop for 5W and ferrite / heatsinks 
> / and ammeter stay cool and low...
>
> Next time, TNX de DaveR AA1A
>
>
>
>
> On 11/2/2018 3:24 PM, N1BUG wrote:
>> Hey folks, it's that dim bulb up in Maine again! Ya know, we haven't
>> seen the sun in so long everything here is dim. And waterlogged. I'm
>> sure the answer to this is out there on one of the info sites but I
>> am not finding it in a form that speaks to me.
>>
>> I want to design an antenna impedance matching transformer for 630
>> meters. This will go between the coax and the variometer. I believe
>> a single 2.4" OD core of #77 material is sufficient at power levels
>> below 100 watts. Or maybe not, as I believe this depends on core
>> saturation which is related to number of turns. Hmm. That brings us
>> to the matter of how many turns. I believe the rule of thumb is that
>> the 50 ohm side should have an inductive reactance of at least 10
>> times 50, or 500 ohms. That would mean 7 or 8 turns minimum. The
>> antenna system resistance on 630 meters does change over time, but
>> not over a wide range. To that end I would like to have taps to
>> adjust it, but I do not need a wide range and prefer the ability to
>> concentrate on the range of resistances I will actually see. I would
>> like to do this with only one tap switch on either the primary or
>> secondary. This would dictate having more than 7 or 8 turns on the
>> 50 ohm side in order to avoid having the impedance ratio change in
>> large steps. I have been through the math on ratios. Something
>> around 14 or 15 turns on the 50 ohm side would give me the matching
>> range and adjustability I want using the core and switch I have.
>>
>> My question is, what is a practical upper limit for the number of
>> turns? Is this limited only by core saturation? Or are there other
>> factors I need to consider? I will admit to feeling a little shaky
>> on use of the core saturation formula, but *think* I can navigate it
>> from the notes I made last year when someone kindly walked me
>> through an example. I just need to know if core saturation is my
>> only worry with regard to using more turns.
>>
>> 73,
>> Paul N1BUG
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>
>
>
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