PLL unlocking-exciter common problem!

[Radio Garfield]

Hello folks, hope you are all fine!

http://electronics-diy.com/8w-pll-stere ... mitter.php

In the link above is famous PLL exciter. I have one complete box with this exciter and BLF278 PA. Problem is, when ever I reach to about 200W out of PA unit, PLL of the exciter goes unlock. Probably RF energy breaks the loop. Exciter is in its own metal enclosure and has its own 13V power supply.

I had similar problem before with another exciter like this, when it was unlocking with its own full power of about 6-7 W! I saw that people wrote on forums that they have this problem also. One German guy solved it by soldering the case of both crystals to the ground. I did the same thing but it dont solve the problem for me.

This exciter in the box, that I am talking about, is made on the single side PCB and it is just the same like the one on the picture on the link at the beginning of this post. It has the same metal enclosure and same parts, on the same PCB.
Only thing that is missing is the feed trough capacitor for the power line. It is a bit complicated to remove the exciter outside and place that capacitor, so I hope that I will find the cure before that option

Do You guys have some experience with problems like this on this exciter? I have hit the wall right now!

Small editing: Just for the info, here is the topic on this forum, where you can see the pictures of the complete box. Problematic exciter is there on the photos.

viewtopic.php?f=11&t=1567

Thank You.

[sinus trouble]

Hello Mr Garfield!
I am no expert on these exciters but it could possibly be that your supply voltage is dropping when the PA start pulling current?
From what I know? The PLL voltage to the varicap goes up in increments when tuning, as you reach the top end of the band the varicap voltage can be equal or close to supply?

This may not be the symptom? but worth checking?

[sinus trouble]

This may not be the symptom? but worth checking?

Cause!! Not Symptom!! Idiot!!

[Radio Garfield]

This may not be the symptom? but worth checking?

Cause!! Not Symptom!! Idiot!!

Hehehe, Dont be so rude on your self
Thanks for tip but that should not be cause. Exciter have its own power supply.

[sinus trouble]

Haha! Ocasionally my brain can be genius, but mostly its in standby!
The only other thing I could suggest? As the exciter is not 'No Tune' the input of the PA could be presenting the exciter with a less than ideal 50ohm match?
You could try tuning the exciter alone on a dummy to max forward power @ your frequency? Once set then connect to the PA and proceed with tuning the PA only!

I hope this is of some help?

[Albert H]

It's almost certainly RF getting into the PLL. You may have to put the PLL in another part of the case - or even outside the case altogether! Check your earthing. Make sure you've got a proper Star Point earthing scheme. Also filter the DC going into the PLL box - break into the power lead just inside the case and tack on a 1n from the power lead to the box. This will help to strip any RF off the DC supply.

[Radio Garfield]

All right, I will try those tips Albert. Many thanks.

[Shedbuilt]

If it's as per the linked thread, the ribbon cable is another likely source of RF pickup, so if you can unplug it at the driver board end, and temporarily at least use the on-board switches (without the front panel switches and display, to set frequency etc - if necessary), I think that's also worth a try.

[Radio Garfield]

If it's as per the linked thread, the ribbon cable is another likely source of RF pickup, so if you can unplug it at the driver board end, and temporarily at least use the on-board switches (without the front panel switches and display, to set frequency etc - if necessary), I think that's also worth a try.

Hello. Well, we have a winner.
That ribbon cable was the problem. When unpluged from the exciter everything is working fine and PLL is stable. I will try to put ferrite bead or some other suppressor to see will it work with cable.

Many thanks for good tip.

[Maximus]

Had a similar problem with the 15w PKBEE exciter. At high power levels the control became unresponsive. I fitted it in a separate enclosure and scrunched up the ribbon cable.


Sent from my iPhone using Tapatalk

[3M amateur]

If it's as per the linked thread, the ribbon cable is another likely source of RF pickup, so if you can unplug it at the driver board end, and temporarily at least use the on-board switches (without the front panel switches and display, to set frequency etc - if necessary), I think that's also worth a try.

Hello. Well, we have a winner.
That ribbon cable was the problem. When unpluged from the exciter everything is working fine and PLL is stable. I will try to put ferrite bead or some other suppressor to see will it work with cable.

Many thanks for good tip.

Hey, I had a similar problem with a transmitter that had noise for when you joined the LCD display but was quiet without. And I tried to ground the LCD earth to the chassis, and then became silent. Try it, I think it's working.

[Radio Garfield]

Wow, lot of problems with display! Ok, I will try to ground it. Will let you know about the result. I am busy with some other stuff.

Thanks folks.

[radium98]

Radio Garfield sorry for asking you say you get about 6-7 watts can you what you have done i built this one year before all is good but cannot get more than 2-3 watts in good case with original genuine c1971
be aware from fake palso c1971 chinese rubbish i bought some and all go to recyclebin

EbqW99d.jpg

for the first picture any one can modify the hex file like this up to 300 mhz ?

[Radio Garfield]

Radio Garfield sorry for asking you say you get about 6-7 watts can you what you have done i built this one year before all is good but cannot get more than 2-3 watts in good case with original genuine c1971
be aware from fake palso c1971 chinese rubbish i bought some and all go to recyclebinEbqW99d.jpg

Let me start from the end. Yes, lot of junks on ebay from China. I have few sellers who have good products and I keep buying from them.
BLF177 and RD15HVF can be found good.
2SC1971 bought from some seller from Bulgaria and they are old stock good pieces.

Now about this exciter. Yes, it can be done to give 8W. Lot of things are must to achieve that power. First good drive-power from BFR96 and good output stage from 2SC1971. Its that simple.
It all depends on your previous experience and knowledge about RF electronics. Good trimmers and capacitors, short connections, big and good grounding, quality PCB etc. Lot of small stuff that make the difference between good and poor work. Maybe you can place the photo and we can give our suggestions on your work.

Edit, while I was writing this post You uploaded the photos. We will make some comments on it.

[radium98]

no bro dont comments on theses photos they were old i will upload new ones
can i ask a fever about an rd15hvf1 amplifier layout to build to get 13-14 watts ?


and what about the hex file i asked can u modify i need that to work on studio link .

[Albert H]

Radium - the code can be easily modified to cover other bands. However, the board isn't really suitable for 300 - 400 MHz, you need quite a different layout. I used to link in the TV bands, using boards from gutted police UHF radios modified for wideband deviation. The beauty of using those frequencies is that you can use ordinary TV Yagis at each end. TV Yagis don't look out of place on any building!

[radium98]

so Albert H please modifiy please the hex code to me for such frequency i want try a thing thanks never mind that is suited or not yess it is not a uhf design if not so hi i prefer if u modify code for 108-200 mhz
thanks

[MC Spanner]

so Albert H please modifiy please the hex code to me for such frequency

@Albert, at some stage during this work can you please post your disassembly of the hex file.

However, the board isn't really suitable for 300 - 400 MHz, you need quite a different layout.

An understatement. Matching, PCB material, decoupling, stitching, 2SC1971 ft = 175MHz, yaddah, yaddah.

[yellowbeard]

Freddo did a TSA5511 PLL with a PIC16F628 back in the day, hex code is on the page and allows for a few different I.F. offsets - there is no R.F. circuit with it though...

Code: Select all

http://home.deds.nl/~radio102/freddos/default.htm

[Radio Garfield]

Freddo did a TSA5511 PLL with a PIC16F628 back in the day, hex code is on the page and allows for a few different I.F. offsets - there is no R.F. circuit with it though...

Code: Select all

http://home.deds.nl/~radio102/freddos/default.htm

Good link. Lot of nice projects there. There is also thing that @radium98 wants so here is the answer for him also.

Thanks again.