I've built my own PTO without 3d printer. I used? 4 small PCB boards (25x20mm) using a 9mm diam. old? pen and 2 nuts soldered.
Instead of common nuts I used 2 parts from Fisher gussets diam 6mm. I suppose it's faster to built than a 3d printed one, and is as much robust.
If PTO must be screened ( low cost is again PCB panels) why not use? PCB also for all the parts??Using? 3X470pF
common ceramic capacitors my PTO is not only very instable, but also stops to oscillate when the brass bolt is inside. With better capacitors it oscillates without problems,
but still is very instable. Supposing also C27 and C29 capacitors can be the problem, I? deleted D2, R16 and C29 and connected coil to the gate of Q6, and pin 3 to?
the center of coil with a 1K resistor. With same C31 used before ( not yet polystyrene) now is much more stable. Soon I will post pictures.
Paolo

Hi Farhan,
what a pleasure !
In attachement a pic of my PCBs.
My PTO has a coil 30mm long , 9mm diameter, 10+30 turns? for 1.997 KHz without brass inside, turns are 24mm long.

What the dimension of your 3d coil?
With some more works bigger PCB? can be built 20% smaller. I used Easyeda, Flatcam, Cncusb and K2cnc milling machine, yes it is PCB milling.
Can you please answer also my other questions? Thank you
Paolo? from Italy

OOOPS; I forgot..
blu capacitor are for teast, wayting polystirene capacitors, 6mm diameter brass bar, etc...

AS i told you, I'm wayting for polistyrene capacitors and 6mm diameter brass, and yes, with a test using? a small
3mm diameter brass I can see frequency increase when pushing bar inside the coil.
The iron bolt in my pic is used only to align parts.
Here the cost till now ( total cost items plus expedition) in EURO
10 zener 5.6V smd? ? ? ? ? ? ? ? ? ? 3.90
10x MMBFJ310? ? ? ? ? ? ? ? ? ? ? ? 12.06
100x MMBT2222? ? ? ? ? ? ? ? ? ? ? ? 5.40
10x 5MHz smd xtals? ? ? ? ? ? ? ? 10.53
Bar 6mm diam. brass? ? ? ? ? ? ? ? 11.00
5x polystirene capacitors? ? ? ? ? ?19.59
--------------------------------------------------
TOTAL COST TILL NOW? ? ? ? ? ?62.48 EURO
I still had all the other parts, but now I? need to buy parts for RF TX? board ( LP filter, transformers) and a suitable metal box.
Sorry, forgot,? I have to buy also the small frequency counter, that is 11+3? euro from China, I have to wait usually 40 days.
A programmable one costs 49.51 euro.
I can drill, mill and/or silk-screen the front plate.
I still have a Baofeng mic+loudspeaker payed little more than 12 euro.
I suppose the final cost will be much more than estimated 100 euro ( today 1 euro= 1 USD) only for? buyed parts.
BITX40 was 59 USD,? uBITX V6 basic kit complete without box but with everything ,microphone , display, etc is 160 USD.
Paolo

Years of building radiosn with VFOs/PTOs there are tricks.

The big one is having a stock of N750 caps in the 1-47pf range.
The N750 means negative 750ppm change for degree C.? They
are the fix for VFOs that drift down with temperature.? The amount
of N750 cap is experimental too much and it drifts up, too little
and it drifts down.

There are only two types of caps I will use for stable VFO, Silver mica,
Polystyrene,? some quality COG types are ok.? Generally ceramic unless
class 1 are drifty and some have serious change with temperature and
applied voltages.

As to PTOs the in-out screw woks well but not from the front panel.
The solution is mount the PTO and screw assembly add a pin to the
end of the screw and slide that into a slotted tube that can rotate but
no move back and forth.? I use a 1/4" (.25" ~5.56mm) tube and the
screw is typically 8/32 brass of I thread some aluminum rod.? FYI since
the slotted tube is fixed but rotates its easy to add a linear pointer
style dial (pointer, track to ride on and dial cord with spring for tension).

Allison
--
Allison

开云体育

Didn't need a vernier.? Knob was on the tube direct.? one turn of knob is
one turn of the screw.? Keeps it simple and for the PTO I built one turn is
maybe 5khz so its fairly slow..

Allison

Never had a noise issue but if there was the easy fix would be a long?
low tension expansion pring indie the tube to keep a metallic contact
and also keeping the screw under some tension.

Keep in mind the screw is inside the tube making contact as well as
the pin to assure it turns.

Allison
--------------

On Tue, Sep 13, 2022 at 10:35 AM, ajparent1/kb1gmx wrote:

As to PTOs the in-out screw woks well but not from the front panel.
The solution is mount the PTO and screw assembly add a pin to the
end of the screw and slide that into a slotted tube that can rotate but
no move back and forth.? I use a 1/4" (.25" ~5.56mm) tube and the
screw is typically 8/32 brass of I thread some aluminum rod.? FYI since
the slotted tube is fixed but rotates its easy to add a linear pointer
style dial (pointer, track to ride on and dial cord with spring for tension).

Hi Allison -?

VFOs and now variable inductor VFOs have become a bit of a mania for me lately!? Thanks for the description of the mechanism but if you could post a picture it would be very helpful. I'm having trouble visualizing what you describe.

73 and thanks for all you do for the hobby!
Dean
KK4DAS

Nope, not taking the screws out.? Seriously while it works copying it would
how I torture you.? Everything is built from my not near 55++ years
accumulating junkbox.

The idea is not original.?

You have images of the screw and coil assembly and asume the screw has a hex nut.
Now if you put a deep socket with the correct hex inside shape you can rotate the screw
in or out without the socket doing same.? Imagine the socket on a shaft with a bearing
and a knob.

IF the screw only had a pin at its end we still have something we can? grab and turn,
so if a tube with a long lengthwise slot were slid over that pin we can turn the screw
but the tube does not have to go in or out.

There are several ways to vary that.? The kit described and sold uses a threaded bushing
as a fixed rotary element with the knob.? A screw threads in and out of it when it turns.?
The intermediate board with nut prevents the retained threaded screw from turning see?

the manual for how that one works.? ?

One of many ways to solve this problem.? The real trick is to do it with easily obtained
materials and limited tools (hobby saw, files, drill).? FYI the slotted tube was done using
a Dremel tool and a narrow cutoff wheel, very carefully to keep it straight.


Allison
------------------
Please use the forum, offline and private will go to bit bucket.

Indirectly driving the tuning slug is one way to solve this.



There is a 3D printed solution for everything these days :)

开云体育

Winding the coil with a taper give an even frequency change for a given movemrnt of the tuning screw/slug.
In the dark ages like Collins, Drake PTO or Tentec PTOs the goal was a precision linear change of some value.
That made mechanical dials both accurate and easier to provide a calibrated scale.

With a digital display it has less significance.


Allison
------------------
Please use the forum, offline and private will go to bit bucket.