Date   

Re: Variable Vacuum Capacitor (VVC) Maintenance

K4MJA
 

Mine does this...I don't know if this is normal. Supposed to be 4-100pF.


Re: Variactor diode for receive loop

Immo, DL5KB
 


at the first drawing I missed the blocking C. Thanks to Gary!
73


Re: Variactor diode for receive loop

Gary W9TD
 

DC blocking capacitor required or else loop shorts out the varactor bias.
Gary
W9TD


Re: Variactor diode for receive loop

Immo, DL5KB
 
Edited

hi Simon,
main issue will be to find a Varicap which gives up to 50pF. I did a little calculation: Loop consisting of thin wire, i.e. 1.5mm diameter and loop of 60cm with 3 close windings will have abt. 15µH. For tuning it to 7MHz you need 35pF.
The blocking inductivity should be abt. 10 times the loop inductivity. 

I don't believe, that there will be any issues, except if you transmit on similar frequences nearby. 

So, do a try and let us know your success or issues.
73
Immo


Variactor diode for receive loop

Simon
 

Does variactor variable capaciance diode has high Q factor that is comparable to air cap?   

Can it be used for receive loop?  

Prelimary loop calculator shows signal at says -30 dBm will induce tens of mV and NOT significantly affecting the cap value.


Re: Variable Vacuum Capacitor (VVC) Maintenance

Immo, DL5KB
 

And another picture of COMET capacitors:


73
Immo


Variable Vacuum Capacitor (VVC) Maintenance

Immo, DL5KB
 
Edited

Hi All,
 
I see an increasing use of variable vacuum capacitors and subsequent reports of issues with driving them mechanically.
Main issue is according to my experience directly originated to the fact "NOS". These pieces are partly more than 30 years in their package and never moved since this time. The grease of the bearing and the thread is resinified due to age.
 
For renewing the lubricaion, the old grease has to be removed and substituted by new bearing grease.
 
Procedure:
- turn the capacitor to maximum capacity
- remove the srew by continuous turning ccw
- remove the bearing cap and the bearing
- clean the bearing by "bathing" in benzine or similar
- clean the thread with benzine soaked cloth and perhaps old teethbrush :-)
- relubricate with bearing grease
- reassemble the bearing, cap and thread
 
See and feel a new variable vacuum capacitor!
Any NEMA 17 stepper is able to drive it, even ungeared!
 
For information a scheme from american facturer Jennings, russian ones are similar.
 
Good success!

73, Immo


Loop controller and ICOM IC-705

Matt 9V1MH/VK3AMH/YF2AAH
 

Greetings

has anyone configured the controller to work with an IC-705 - which has a single USB port that has split channels for CI-V and GPS data i.e. 2 data streams one usb port

I need CI-V data control and GPS for digital mode use portable (no wifi or mobile coverage)

I am thinking com0com may do some/all of this but not sure how it would be configured

73

Matt


Re: program modification

Piotr Bagniewski
 

Hi Immo, 
I wasn't sure how the measuring works, that's why asked for help.
If  you really think that this wouldn't work, I will not bother, but my impression was that it should.
Does anyone else have other  opinion on SWR via CAT command?



On Tue, Mar 9, 2021 at 01:36 AM, Immo, DL5KB wrote:
hi Peter,

fine idea I think, but:
SWR-reading during tuning is required permanent.
The interface is not able to pull the SWR-data at such short intervals.

This will be the scenario:
1. pull SWR-data,
2. make a step,
3. pull SWR-data,
4. make a step, etc.
If endpoint of tuning interval is reached caused by increasing SWR, backlash-steps are inserted, to go back to the best adjustment. And a new approach...

I presume, you won't be happy of this, even if it's possible.
My suggestion: Take a little bridge from kits and parts, comp a little metal enclosure and you will get happy.

If you wouldn't have additional RF-cables at your bench, connect the bridge per cable and use it remotedly. Works fine, while regarding a good shielding and right grounding.

Good luck
73, Immo


Re: program modification

Immo, DL5KB
 

hi All,
this shows the connection to a remoted bridge:


Re: program modification

Immo, DL5KB
 

hi Peter,

fine idea I think, but:
SWR-reading during tuning is required permanent.
The interface is not able to pull the SWR-data at such short intervals.

This will be the scenario:
1. pull SWR-data,
2. make a step,
3. pull SWR-data,
4. make a step, etc.
If endpoint of tuning interval is reached caused by increasing SWR, backlash-steps are inserted, to go back to the best adjustment. And a new approach...

I presume, you won't be happy of this, even if it's possible.
My suggestion: Take a little bridge from kits and parts, comp a little metal enclosure and you will get happy.

If you wouldn't have additional RF-cables at your bench, connect the bridge per cable and use it remotedly. Works fine, while regarding a good shielding and right grounding.

Good luck
73, Immo


program modification

Piotr Bagniewski
 

Hi,

I just got the PCB in the mail today, and I will continue with the rest of components.
I just have a question if there is someone in the forum who knows hot to program the Teensy.
The original design calls for a SWR bridge, but there is an option to get the SWR from the radio using CAT commands.
I will have an Arduino library for yaesu that includes the SWR reading from the radio, but I do not think I would be able to modify the 
code to include it in the program. 

I am looking for someone familiar with the original program who knows how to modify it.

Thanks.


Re: Non Linear Vac Cap?!

K4MJA
 

Interesting! I have the same or very similat cap and it is hard to turn. I will be try to lube it tonight!


Re: Non Linear Vac Cap?!

Barry - 2E0IDE
 

Immo

 

Thanks for the comments and advice. This is my first attempt at building a Loop. I used a modified “Work Mate “ to bend the copper tube as per pic(an idea from  John G6KJK) with heat shrink instead of paint. All copper fittings were hand-made, and all plastic mounts and loop fitting were home designed and 3D printed.

 

I did wonder about the copper band on the drive end and will take your advice and re-design.

 

I’m using a coax Faraday Loop coupler that is a slightly squashed circle (squashed even more than the pic - It does improve SWR). The coupler is designed to be easily removable so that I can experiment with gammas etc.

 

After the lubricant fix on the vac cap, the SWR on 20M is negligible but rises slightly for the higher bands.

 

I’ve had good contacts into Eastern Europe on my meagre 50 watts allowance.

 

Overall, a very enjoyable project and the controller is to be commended. Arduino based rotator next.

 

Once again thanks for all the help and advice.

 

73

 

Barry - 2E0IDE

 

 

 

From: loopController@groups.io <loopController@groups.io> On Behalf Of Immo, DL5KB
Sent: 07 March 2021 15:03
To: loopController@groups.io
Subject: Re: [loopController] Non Linear Vac Cap?!

 

Barry,
your'e welcome. This experience is part of my worklife. 

By the way: beautiful work, your tuning-box.
Perhaps a little remark to this solution. The connection to the head of the capacitor elongates the loop on this side. So the mechanical middle of the loop is shifted half the length of this connection to this side. It may (I say it may!) change the reachable best SWR, because the coupling loop now is not at the point of zero of the loop. Using a gamma-match, you should search the new zero on the loop, with a coax coupling-loop it may have no such importance.
With an earlier built, I used a gamma-match and had to shift it abt. 3 inches for good result. The picture shows my first solution with a vac-cap on the bench, just with an ungeared Nema 19. My loop today has a 5:1 geared stepper and a coax coupling-loop.
73, Immo


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Re: Non Linear Vac Cap?!

Immo, DL5KB
 

Barry,
your'e welcome. This experience is part of my worklife. 

By the way: beautiful work, your tuning-box.
Perhaps a little remark to this solution. The connection to the head of the capacitor elongates the loop on this side. So the mechanical middle of the loop is shifted half the length of this connection to this side. It may (I say it may!) change the reachable best SWR, because the coupling loop now is not at the point of zero of the loop. Using a gamma-match, you should search the new zero on the loop, with a coax coupling-loop it may have no such importance.
With an earlier built, I used a gamma-match and had to shift it abt. 3 inches for good result. The picture shows my first solution with a vac-cap on the bench, just with an ungeared Nema 19. My loop today has a 5:1 geared stepper and a coax coupling-loop.
73, Immo


Re: Non Linear Vac Cap?!

Barry - 2E0IDE
 

Immo

 

You’re a star! Thanks

 

Problem solved – 30 year old grease! I oiled the thrust bearing and screw thread with clock oil, then manually ran the cap full travel several times.  Re tuned all the range settings with the swr tune button and stored results. 14.0MHz to 14.1MHz was accurate to 24HZ which is plenty good enough for me.

 

73

 

Barry – 2E0IDE

 

 

 


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Re: Non Linear Vac Cap?!

Immo, DL5KB
 

Barry,
your data as diagramm...
73
Immo


Re: Non Linear Vac Cap?!

Barry - 2E0IDE
 

Thanks for the feedback Immo.

 

I did consider slippage in the steeper. When I first replaced the air cap with a vac cap it had a non- geared stepper(i.e. 1.8 degrees) and I got very similar results. Thinking it was a torque problem I replaced the stepper with 5:1 geared stepper.

I can turn the vac cap by hand but there is quite a lot of resistance, so you could be right that there is still slippage,  even with the increase torque of the 5:1 gearbox.

 

There is a plastic cap on the drive end that looks as though it may be removeable. Perhaps this is where I can re-lubricate. Any thoughts?

 

Attached is a plot of the 20M band after pushing SWR tune and storing,  at each step – it’s linear across the band! But when I went back to 14.000 to check it, the SWR was NFG. So it does indeed look like slippage. Controller stepper settings are 60rpm, 4x, 4, so I don’t think it is a speed problem. Stepper backlash 300.

 

73

 

Barry – 2E0IDE

_,_._,_


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Re: Non Linear Vac Cap?!

Immo, DL5KB
 

hi Barry, 
I tried to retrace your data as far as possible. My experience with vaccum-Caps is another, then your data show. I believe, that you have some slip in your actuation. I did a little calculation for frquency per step and saw several glitches:  i.e. from 14.125 to 14.150 are 8.704 steps, also from 14.2 to 14.225 you have documented 1.416 steps. There are some points more.
Is it possible, that the drive-shaft turns loose sometimes or you go with to high rpm, that the stepper looses steps (glitches)?
The vac-caps are normally linear from maximum C down to 5% of C. At the last part (min C) there start, depending on construction, non linearities.
If your cap is NOS, it is also possible (and normal), that the lubrication of srew thread has got old and stiff. You should renew the lubrication. 
And yes, the controller makes a linear interpolation of the steps between two stored values to get the value for a not stored frequency. So you have to take the more programmed steps, the nearer to the minimum of cap.
So take a look to your system.
Good luck!
73, Immo


Re: Non Linear Vac Cap?!

Barry - 2E0IDE
 

Guenter

 

Thanks for the reply.

 

My Vac Cap is ex Russian – built 1991 and still in the box certified for 3KV but tested up to 5KV  and unfortunately is very non-linear.

 

I’m assuming the tuning code takes the next lower rang, next upper range and calculates accordingly. I’ll have to take a look and see if I’m correct. IF someone can point me to that section of code I’d appreciate it.

 

I hoped that adding 25KHz range steps at 20M would help but it did not .Perhaps I’ll have to add more.

 

73

 

Barry – 2E0IDE

 


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