[600MRG] Transformer design

Fri Nov 2 21:36:21 EDT 2018

Now there is a guy who can explain this phase!!

On 11/2/2018 7:19 PM, kl7aj at acsalaska.net wrote:
>
> Winding coils has been the main bang at my QTH for a long time. HI!
>
> Eric
> ---
> Eric P. Nichols, KL7AJ
> AlasKit Educational and Scientific Resources
> 3763 Lyle Avenue
> North Pole, AK 99705
> (907) 488-0483
> (907) 371-7120
> http://alaskit.co
>
>
>
> On Fri, 2 Nov 2018 19:16:17 -0400, Dave Riley wrote:
>
>     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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