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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Mar Tue 20, 2018 2:07 am 
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1500kHz is 666ns per cycle. 22/666 = 3.3%, so better than 52/48 duty cycle. I know I'm the guy saying anything other than 50/50 is unacceptable but that feels like a pretty small error. I thought your earlier traces looked much worse.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Mar Tue 20, 2018 2:32 am 
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richfair wrote:
I thought your earlier traces looked much worse.


They were worse. The earliest traces were on the Motorola PLL and the later / current ones on the TI PLL which is much better.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Mar Tue 20, 2018 9:09 pm 
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Rich;

I was thinking about your circuit to use your signal generator but don't have all the parts needed. But it did make me wonder how much output my BK Precision generator had. It outputs 90 mv. It also has a monitor output that I keep connected to my frequency meter so I can set the frequency exactly where I want it. Just made me curious so I measured the output of the monitor output. HOLY COW! It is 2.8 volts PP and the attenuator does not control it. I hooked up a single 7414 inverter / Schmitt trigger and got a solid square wave @ 4.5 volts out that was almost exactly 50%. Connected that to the transmitter and it not only does the transmitter work but the output of the 7414 stays at a solid 4.5 volts and the antenna tuning has no affect on the waveform. Dang. Didn't see that coming.

So another confirmation that all you need is a good 5 volt square wave from any source to feed this transmitter.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Mar Tue 20, 2018 9:28 pm 
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Holy cow, that is fantastic! Sure makes it easy for you. I've noticed that as long as rf drive squares are at least about 3 volts, with fast rise and fall, the transmitter works well.

My grungy old Heathkit beater gen doesn't have any fancy outputs like that. I bolted on an extra BNC for a counter which is just a take-off from the top of the attenuator pot, and so is around 100mv "sine". Counter is perfectly happy, thankfully.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Mar Tue 20, 2018 10:41 pm 
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richfair wrote:
1500kHz is 666ns per cycle. 22/666 = 3.3%, so better than 52/48 duty cycle. I know I'm the guy saying anything other than 50/50 is unacceptable but that feels like a pretty small error.
I feel so special when I quote myself! :D
So, for rf drive I have a choice of perfect squares or somewhat-adjustable pulses. The pulses are not very symmetric, at best I can make them about 30/70. Having such a unequal duty cycle messes with the antenna peaking and also with audible distortion. The antenna peak is at one point, lowest audio distortion happens when tuned to one side of the peak and worse on the other side. I don't know why that is exactly but there is no doubt in my mind that rf drive symmetry is important, but I'll be surprised if 52/48 is even noticeable.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Apr Mon 02, 2018 5:49 pm 
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I finished up Macrohenry's Frequency Synthesizer and got it into a case as a standalone unit rather than integrate it into a transmitter project. My reasoning is that the transmitter section is now able to use Oscillator chips, Frequency Synthesizer, or Signal Generator as the source for the RF frequency base. So, I am building the transmitter to work with all three and selectable by jumpers in the transmitter. I had this case left over that once housed a Cisco Digital Media Player. The top is held on by thumb screws so it requires no tools to open it and set the DIP switches. Inside the case is an adjustable regulator so I can run the synthesizer at 9 volts for the transmitter or up to 12 volts if needed. Posts on the back are the 12 volt input and the PLL output. Transmitter will have a socket for the ECS Oscillator so I can swap out the 3 frequencies I have available.


Attachments:
synthb.jpg
synthb.jpg [ 58.25 KiB | Viewed 569 times ]
synth.jpg
synth.jpg [ 38.62 KiB | Viewed 569 times ]

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Apr Tue 03, 2018 12:11 am 
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Location: Mesquite NV 89027 (from Coventry, UK)
Very nice Rick!


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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Apr Tue 03, 2018 2:08 am 
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That's the coolest job I've seen in a long time. Case is perfect. JEALOUS!


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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Apr Tue 03, 2018 2:17 pm 
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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Apr Wed 04, 2018 1:41 am 
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WOW Rick that is superb! Thumbs screws for access, size is perfect, ventilated, stylish, I love it. I don't suppose you have another one of those cases to stack your transmitter in?

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Apr Wed 04, 2018 2:20 am 
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richfair wrote:
...... I don't suppose you have another one of those cases to stack your transmitter in?


As a matter of fact I do have another one. Great idea. The transmitter I am currently building won't fit but I could do one just for the synthesizer and pair them together. Thanks for the thought.

I think that will put me at about 6 working transmitters on hand. :shock: Just can't shake the urge to build when I see an interesting design.

Sidebar; These Cisco devices were part of a project I worked on years ago and they became obsolete. I held on to a couple of them "just in case" they might be useful "someday". Worked out well this time but I have way to much "just in case" and "someday" junk!!! Wish I was better at knowing what I need to hold on to and what to trash. Always seems that when I trash something I will need it within a week.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Apr Fri 06, 2018 12:35 am 
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Transmitter is in final form and working as planned. There are a couple of adaptations. First is the green wire inductor at the top. I used 1/2" delrin rod and drilled it out for the 3/8 inch ferrite core. This is the form for the inductor. On the end of the ferrite is a cap made of the same delrin to connect the ferrite to the 6-32 threaded rod. The delrin block on the left is drilled out to 1/2" to mount the inductor form. The block on the right is threaded 6-32 with a knob on the outside to adjust the inductance. Just below the variable inductor is a blue screw terminal that holds a fixed inductor. To cover the entire broadcast band requires taking it in chunks. The fixed inductor is 220 uh and the adjustable inductor is 4 uhto 80 uh, so together 224 - 300 uh which puts the adjustment centered for the 1228 kHz frequency it is currently set to. I can loosen the two screws holding the inductor and swap it to tune other portions of the band. I suppose a band switch would be more elegant but I don't have one and don't expect to change frequency very often. The variable inductor tunes in very small increments and peaks the output well so I have no need for a variable capacitor with this setup.

The transmitter is built to accept its RF frequency from an ECS oscillator chip, Signal genterator, or Frequency synthesizer. On the right is the socket for the oscillator chip. Just to the left of that is a 7414 Schmitt trigger with adjustable threshold to convert the signal generator to a 5 volt PP square wave and adjust its symmetry. I am using several jumpers to select the input I want and connect it to the transistor.

Since we pretty much settled on 9 volts being a good operation level I replaced the adjustable power supply on the prototype with a 7809 for the 386 and 7805 for the 7414 and ECS chip. The transmitter is fed by a well filtered Astron 12 amp 12 volt linear supply.

Front panel is not complete. I am waiting on a 200 ma meter to peak the antenna and monitor power level. Case is a weather proof box I found at a surplus store and got at a bargain price.

Edit: I am testing one of these for possible install in my transmitter. It eliminates the wall wart for bluetooth, mp3, iPhone, etc. It is powered from the same 12 source as the transmitter. I am hearing no noise or hum from it. Originally I bought this to add to my friend's old DeSoto car so he can charge his phone but decided to test it in the transmitter.

https://www.amazon.com/gp/product/B01N6S2SNM/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1


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transmitter-001.jpg
transmitter-001.jpg [ 96.73 KiB | Viewed 508 times ]

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Last edited by black85vette on Apr Fri 06, 2018 1:38 am, edited 1 time in total.
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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Apr Fri 06, 2018 12:57 am 
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Location: Mesquite NV 89027 (from Coventry, UK)
Nice work Rick!


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