[600MRG] Transformer design

Sat Nov 3 05:23:29 EDT 2018

You are correct, Frank, tnx for QC..

"Fine tuning corrects fuzzy math"...

On 11/2/2018 10:12 PM, Frank Lotito wrote:
> Er, I think if my memory serves me correct, impedance ratio is as 
> turns squared ... ?ï¿½ 73 Frankï¿½ K3DZ
>
> Get Outlook for Android <https://aka.ms/ghei36>
>
> ------------------------------------------------------------------------
> *From:* 600mrg-bounces at mailman.qth.net 
> <600mrg-bounces at mailman.qth.net> on behalf of Dave Riley 
> <dave.riley3 at verizon.net>
> *Sent:* Friday, November 2, 2018 9:36:21 PM
> *To:* kl7aj at acsalaska.net; 600mrg at mailman.qth.net
> *Subject:* Re: [600MRG] Transformer design
>
> 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
>> ï¿½ ---
>> 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 )ï¿½ 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 =ï¿½ 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 forï¿½ 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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