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I think the curves on Diz's page are in the best format for varactor capacitance. We normally consider the voltage input linearly. If I'm graphing one, I automatically mark off the V (x) axis in evenly spaced volt increments. But I'm normally looking for something different on the output. Marking the C (y) axis linearly makes no sense. We are rarely looking at the linear response of a varactor because we aren't really concerned with capacitance. We're normally concerned with the resulting resonant frequency response in a tuned circuit. Log/linear can help us with that.

Most of the time, I want a frequency readout to be linear. A varactor capacitance with a non-linear response to voltage is going to give me that. On Diz's graphs, I see a linear voltage input. If I see a fairly straight curve for C, I'm probably going to get a fairly linear frequency response. So log/linear makes sense. If he used linear/linear, you would see a deceptively "hooked" curve that truly shows how C responds, but it wouldn't be as useful for predicting frequency response. Log/linear provides more insight that you can use.

Some of the newer hams may not have noticed the shape of the plates on larger "tuning" capacitors. They weren't symmetrical. They were very oddly shaped to make the dial calibration more linear.

There. Marketing guys owe me one.

BTW, I used to follow your website pretty closely in the Rock Mite days. Fun stuff.

Eric KE6US

Chuck,

It took me awhile to figure out how to make sense of it.
Could be errors, but this is what I am currently thinking:

Here's that equation again, a power of (1/2) means we take the square root:
  Cj =   A/2 * ((2*q*e/(V0-V))*(Nd*Na/(Nd+Na)))**(1/2)

V0 is very close to zero volts so we can ignore it, and V is a negative voltage.
A is the cross sectional area of the cap, Nd and Na have to do with doping levels.
Those all get determined when the diode is fabricated, and won't change for us.
e (epsilon) is the permitivity, should be about the same for all silicon diodes.
q is the charge of an electron, determined back when the universe was born.
If we lump all those constants into a single value I'll call K, we get:
  Cj = K/sqrt(V)

Assume we have a varactor diode that measures 100pf when we put 1 volt across it.
What is the capacitance when we put 10 volts across it?
  At one volt:   K = Cj*sqrt(v) = 100*sqrt(1) = 100
  At 10 volts:   Cj = 100/sqrt(10) = 31.62 pf

Getting back to our original conversation, assume our 10v power supply 
has 0.1v of pk-pk ripple on it.  How much variation in capacitance do we get
with this particular diode for a bias at 1v versus a bias at 10v?

Here's the difference between max and min capacitance at a nominal 10v of bias:
  delta-C = 100/sqrt(10-0.1) - 100/sqrt(10+0.1) = 0.316 pf 

When we adjust the pot to divide down the power supply to give 1v of bias,
we also divide down the noise by a factor of ten.
Here's the difference between max and min capacitance at a nominal 1v of bias:
  delta-C = 100/sqrt(1-0.01) - 100/sqrt(1+0.01) = 1.000 pf 

Conclusion:
Our oscillator will be significantly more sensitive to power supply noise
at low bias voltages across the varactor diode.  This is in spite of the fact
that the voltage fluctuation on a bias of 1 volt is 1/10 what it would be for a 10 volt bias.

Looking closer at the chart posted previously?from Diz's?diodes page



SMD/SMT Varactor 1SV322.?would be a good choice.??

The V/C curve is about the same as the thru-hole?MV-209 or?BB910.

Note that the curves for these two are plotted differently:? SMT part is linear/log and the Thru part is log/linear.? It gives the? plot a different look even though they are much the same.? Depends on what the marketing folks want to emphasize...8^)

Plot them linear/linear if you're curious?about?the "real" shape of the?V/C?curve.
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv

Jerry,? That's a fun equation!

The half-power Sqrt sez is not linear. I can't quite visualize** how the parallel capacitor calculation works out.? I may just have to get really curious and check out the constants and variables and work some examples from the back of the book.

In the meantime, I'll just use my measuring gadget...8^)

Fun Stuff

**I did this stuff about 60 years ago.? Kinda hazy now.
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv

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yea..... we have another term here ...goes way back before BAOFENG showed up here......

Two decades ago we had a local radio club sub-group who gathered once a month for a fox hunt...direction finding ..beacon chasing.

All you needed was an HT to participate so it was a mixed bag of old and new hams and the new guys had no HF gear

so they were looked down upon.... and called "shack on the belt techs"

meaning they were nothing more than HT operators.

I was one of those guys for 2 years.

It was very demeaning.

It really just boils down to respect.

The HF guys totally disrespected me because I couldn't pass a 13WPM CW exam and if I couldn't get a general license I had no incentive to

chase HF.

While at the same time.....? I wrote satellite tracking ..azimuth / elevation.. rotor interfaces ... in assembler... on DOS laptop computers......

so I didn't care about dickheads looking down on me because I couldn't do HF....? I was too busy running circles around them with computers

attached to radios chasing satellites with home brewed hardware...... which was definitely in the spirit of the hobby.

It has been my experience in the hobby of ham radio that IF WE DO NOT MAKE THE EFFORT TO SHARE the hobby many facets then

newbies just have ZERO footing in those facets of the hobby.

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Hi Paul,
Yes, you can measure your torroids.

What I do is put the filter together on the PCB and sweep it using my PHSNA (poor ham's scaler network analyzer).
Did my xtal filter too.
See attached (I hope).
73,
Gary
WB6OGD

I'm building a Norcal 40a and wondering if the toroids can be measured and verified prior to installation. I have an LC meter sitting here on the bench.
Thanks.
Paul VA3ZC

Gents,

Absolutely great!

Thanks for these suggestions and links! If this does not drag them out of Baofeng "Tech-hood" nothing will.
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."

--

I second what Dale says, however (since measuring traps is the subject),? a simple noise generator along with a receiver can be employed to measure traps.? Example:???>.

73.......Steve Smith WB6TNL
? ? ? ? ? ? ? ? "Snort Rosin"

?On Thu, Dec 19, 2019 at 02:07 PM, Dale Hardin wrote:

Chuck,

On page 16 of? ?
there's an equation for the capacitance of a reverse biased diode
? Cj =? ?A/2 * ((2*q*e/(V0-V))*(Nd*Na/(Nd+Na)))**(1/2)

From that, it appears that the junction capacitance is inversely proportional
to the sqrt of the voltage applied (voltage measured relative to V0)
Which to my eye, agrees with those curves.

If you happen to be exceptionally curious, the derivation is in the pages prior.
And if you're lucky, he defines some of the variables and constants in lecture 26.?

Extra credit:?
So, as the voltage across the diode decreases, the change in capacitance due to some delta-V (voltage noise) increases.
But since we are using a resistive divider to create the voltage across the diode,
any noise in the power supply voltage is reduced proportional to that resistive divider.
Which one wins?

Jerry

Don't forget the "noise bridge".? Here is a simple one that can be built out of junk parts:

It is a very useful and cheaply built antenna testing tool.? Dale KS4NS

Gary,? What was the specified part?
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv

Jerry, the shape of the curve in fig 3 is typical of?junctions of non?"purpose built" diodes. (like that term).

I've attached a set of curves from K7QO.? The curve at the bottom is a power diode.? Note that there is not much change from about 5 V so higher voltages don't help much.
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv

Tangential note and thank you to Ray for enabling the "edit" feature for comments. Sure allows one ot revise embarrassing spelling errors and grammatical mistakes.

Never did understand why Chuck did not do that with the original QRP-tech list.
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."

Rob,

Understand that. I coined the term "Baofeng Tech" -- originally defamatory -- mainly because there were a number of guys on a local SoCal repeater system who occupied commute time talking on their Baofengs from their cars with an INSIDE duck resulting in those annoyingly weak signals. Add to the fact that a large percentages spewed inanities and basically babbled on and on. Some/most continued for years without matriculating to other aspects of the hobby. I since left the system to avoid further frustration.

In our day, Rob, we'd call them "lids".

The term as used in this context is much more noble. It seems that some folks are getting into amateur radio and actually developing a keen interest in things like HF and *gasp* even learning CW! Many are receptive to QRP. Its these hams I endeavor to assist.

We found a couple of them last year -- Ed, KM6TNT and Matt, KM6TOA -- who came out for the Zuni Loop FD effort and did a masterful job for so-called Baofeng hams. Both will be back this year and will be eager to work CW. They are among the finest I have met and, I am sure, will rocket past me in op capability.

Anyway, off to try out some of the suggestions offered in this thread.

Happy Christmas and New Year to all!
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."

This is one of the great tools now available to all?for working with? project that you pump and signal into or receive a signal from?and finding out what is really going on.? The 11, 12 ports can provide some significant data..8^)

There are two versions to consider, the NanoVNA-H and the larger screen?NanoVNA-F

Join this group and do diligent research to learn what it's all about.? To begin with, it will overwhelm your senses...

[email protected]?? It would be a good idea to join before you buy your first one.

The VNAs?have a fairly steep learning curve.?If a?VNA is new to you,?it will take some study, reading?messages from an international group, and reading all the instructions?posted in the group files.

Have Fun...
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv

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I don't know about you guys but when I first got a Technician license 21 years ago (after passing 5WPM CW) and I was finally allowed to use a 2 meter HT I

could not purchase a 2 meter HT for anything less than $150.

That $150 was cost prohibitive for me back then.

Over time I observed a number of other hams who were in the same financial position... raising kids... who could not justify blowing $150 on an HT for the hobby.

BUT

now that BAOFENG UV5R costs around $30.......

it just seems to me that this 2 meter HT would be a great stepping stone to indroduce newbies to the hobby of ham radio.

And the WLN and BAOFENG 888s 440 radios are even cheaper.

I pretty much live on a $15 HT now.

Just mind blowing that my first HT cost ten times as much as this one I use now....

and

I had to drive 3 hours to go buy my first HT at HRO in Delaware.

SO

then what?

Newbie....?? FNG ....?? has an HT.....? and asks what else he can do in the hobby... having JUST that one $30 radio.

?PSK31 .....HELLSHREIBER and anything else you want to blast out of FLDIGI.... and SSTV and ? APRS .....

all work fine with BAOFENGs .....

teach them how to build an interface..... NOT BUY... an interface....

and the hobby will no longer be a repeater hobby.

73 Rob KB3BYT

Loading the clock outputs with 50 ohms (such as a 6db attenuator) will make crosstalk and phase noise much worse.
Hence the discussion here of cheap 74ACT and 74LVC series buffers to drive a 50 ohm load.

Hans reports the Si5351 based QCX does pretty good on phase noise, see the last paragraph here:
? ??/g/qrptech/message/326

Apparently much better than a traditional VFO.

If you need better than that for some reason, SiLabs does sell parts that cost more than $1.

Jerry

It's a Military/Viet Nam Era thing. "F---ing New Guy" meaning the newest arrival in a unit.

Also, many, many thanks for the great ideas. I think with the availability and affordability of the antenna analyzers (starting from ~$50 for the Cheap Chinese? ones) and the $20 component checkers or the Chinese L/C meters, that's a viable solution and can easily be argued as a "must have" for the Baofeng Techs who want to branch out and actually learn about antenna and electronics principles.?

I sure wish I has that kind of stuff when I started out as a Novice in 1961!

Again, thank you all for the robust (and informative) responses! And, by the way, thanks Ryan for the great forum. It's really running great!
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."