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Hello I'm new to AM Transmitters and have some questions




 
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Author Topic: Hello I'm new to AM Transmitters and have some questions  (Read 1320 times)
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VA3ACJ
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« on: November 09, 2021, 11:33:05 PM »

Another New Update Nov.17th 2021: Squealing in Transmitter on TX! Can't get on the Air yet, more work to get sorted out.
I tried testing the transmitter last night and it worked fine on the dummy load antenna, then when I hooked it up to the tuner with ladder line it had a type of feed back on the TX. It reminds me of when you have a mic next to a speaker and it screeches! My ladder line comes into the window about 1 and 1/2 feet long right into the back of the tuner. Should I try to shield it somehow? I don't want to be sitting in a room full of RF for that matter either lol. My field strength meter went off scale also, I may try to shield the Mic wires with foil just to see if that may be the cause or is there something I'm missing here? The Audio/(Mic Gain) could not even be cracked a pinch or the squealing with a full TX power out on the mere happens. Again I'll note that everything works fine on the dummy load when testing. Thank you for all your advice for the comments below, very helpful information here.

Old Update: Hi everyone, I'm New to AM Transmitters and looking for advice tip's and tricks,
I'm posting my update of the project for the Mod I did to my Johnson Viking Ranger. I've added a cord with a ground on it and a 5Amp fuse that is RE-Set Type on the "Hot" side that feeds that power transformer. There was limited space to fit everything but I managed to get it all in there. I relocated the cord and used the old location for the re-set fuse. I removed three of the disk type caps (as per instructions from a video I watched) I was wondering if the other small ceramic caps should be removed that are on the other side of the small coils? What do you think? As now it has an "Electrical Ground". I live on a 2nd floor of the building and only have a radiator system to use for grounding things. I was thinking to tie my gear into that hot water heater rad system but not sure if that's advisable or not. Now that I have the electrical cord on the Transmitter there may be no need to add extra grounds as it may cause a ground loop, right?

I may try to install a grounding rod outside at some point in time but the wire going to it would be long like 15-20feet and may act like a part of the antenna system. What is best to use for ground rods? Copper pipe will corrode in a short time and is costly, I may be able to drive something about 4-6feed deep, where as I know 8ft is recommended. What is your best experience with this grounding?

On my closing note if anyone has tips about tuning this "fine business" Transmitter that would also be great. I read the manual and watched some youtube videos it seems the drive should be set for 2.5mA and no more correct? My Diawa Cross Needle PEP watt meter shows 40Watts Carrier and about 60Watts on Voice Peeks into a 1KW Dummy Load Antenna. Is this normal for the Rangers?

I uploaded the schematic as per a request here on the forum and two pictures of the mod. There was no room for me to post more pictures of the process but if you want to see them just send me a request and I may email them for you.

Happy AM'ing
73
VA3ACJ
Samson, Toronto Canada.

 
 


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W1NB
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« Reply #1 on: November 10, 2021, 07:43:31 PM »

Samson,

It would really help if you would post a picture of the pertinent schematic section with the components you are referring to highlighted or circled.
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ve3bkd
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« Reply #2 on: November 14, 2021, 04:03:12 PM »

Hi, Sam
Nice job on your RE-Set Type fuse , its a good thinking .
I would put back does ceramic caps back i don't think  it would  hurt anything if you could still fit in there , but replace them with new small ceramic type .
As for ground you are in an apartment so i personalty would not ground the transmitter and antenna to a water heater if you can run an outside separate ground . keep your RF away from neighbours   .
my 2 cents.
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WD4DMZ
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« Reply #3 on: November 14, 2021, 08:22:38 PM »

Copper pipe will corrode in a short time and is costly,

I used a standard piece of 1 inch copper pipe. Purchased an 8 foot and cut it in half, pounded one end flat on each piece and pounded them in. One 8 is better than two four foot pieces but it seems to work. About two months ago I had to pull up one piece as it was in the way of my neighbors new fence. After 11 years it was was not at all corroded! Discolored but otherwise fine. I used a torch to solder a #12 wire to the pipe and the other end to my stainless ground radial plate with stainless hardware.

Also, I found I could access the utility's 8 foot ground rod at the service entrance to my home. Here I connected to my station with a #8 wire.

Neither ground run is perfect but I have no issues with RF in the shack on any Amateur frequency. It is likely the #8 radiates on some frequency but no problems on Amateur frequencies.

So, a piece of copper pipe is fine for a long time. And it does not need to be perfect.

Rich

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« Reply #4 on: November 14, 2021, 08:30:43 PM »

And if your dirt is mostly insulation (dry, with no conductivity), try using a post hole digger, and refill it with soil mixed with powdered copper sulfate. 

The drive your rod into that. Wink  Two or three is better, space a few feet apart. 

Periodically wet it thoroughly if rain is scarce.

If you can't source copper sulfate, rock salt will do in a pinch.  Make sure your rod is copper or at least copper clad.

73DG
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« Reply #5 on: November 15, 2021, 05:42:14 PM »

If you have access to the actual physical earth......  But no access to the AC service entrance (you know, where the AC is brought in from the utility pole or underground, DON'T go around adding grounds willy nilly.  This is against the NEC.

There is no such thing as an RF ground.

RF is hard and costly to generate, why would you want to shunt some of your costly rf to ground?

Feedline chokes (if using coax) are your friend to force the rf out the antenna.  Your neighbors will also appreciate it as it prevents common mode radiation:  Which is what a lot of people try to mitigate with RF grounds.

To meet code, you have to bond all 'external' grounds with your service ground. #8AWGbis a minimum, and it goes up when breaker sizes go up.  You can get away with not bonding to the service ground by ensuring you have an isolation xformer.

What will help you is ensuring the green wire on your 3 wire cords is properly connected to actual chassis.  Clean, bright chassis.  Not the way astron does it by using a black screw to ground the case through the painted finish, but clean, bright metal (and then put something over it....  Even the wife's fingernail polish works, to keep the connection from corroding). A common mode choke where the antenna feedline exits the station (after the tuner or swr meter, whatever is last) and a common mode choke at the feed point of the antenna will negate the 'rf ground' BS as well as the extended piece of ground wire possibly radiating.  Bonus, it will also minimize noise pickup along the coax.

If using parallel line (ladder line, etc) common mode chokes won't help.  Just ensure you have equal currents at the same point on your feedline.

Adding ground rods that aren't bonded to the service ground is inviting yourself to be open to litigation if something happens and an inspector sees the 'station' ground.

--Shane
KP2 / KD6VXI

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W4AMV
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« Reply #6 on: November 16, 2021, 02:57:37 PM »

Hello Samson,

I received a Ranger I to restore. As received one of the line fuses in the 2 fuse cartridge was blown. No apparent reason. I assumed HV caps were possible fault and replaced. There were issues with the meter switch, the plate current meter position had burnt out contacts. Fixed and proceeded with following the manual and running on a variac and all was well.

About a week latter with the unit still on a variac, I slowly increased the line voltage and at about 90 Vac a loud ZAP and that replaced fuse, blew. What the heck... all was well last time operated. Turns out, one of those ceramic caps on the line TVI filter affair had a chip in its case. The line voltage conducted to the chassis frame from that small crack-chip in that cap. Easy to tell, the ZAP left a nice black trail about 1 inch long on the chassis.

Take care in replacing those caps and do a real close visual on them. Any that have a chip or crack around their surface, replace... or leave them out. No TVI today.

Per DMOD posts... Yes, I used and failed to mention the X type, Line to Neutral Safety Capacitor. They are rated at 250 VAC, and you can get larger. I had these left over from another project. There designed to handle high transients and if they fail, they fail in a "safe" manner. Their body is a thick molded coating.


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Opcom
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« Reply #7 on: November 17, 2021, 12:37:01 AM »

There are certain kinds of caps that are supposed to be used on mains bypass, in mains filters etc. They have some marking on them, I can't recall, but are called Class X and Y, I think, these pages might apply:

https://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/

https://justradios.com/safetytips.html
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DMOD
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« Reply #8 on: November 17, 2021, 12:13:10 PM »


Take care in replacing those caps and do a real close visual on them. Any that have a chip or crack around their surface, replace... or leave them out. No TVI today.

I have also noticed that a failing or failed capacitor may have one or more white or dark spots on it, the spots being about the size of a #2 or larger pencil dot, and usually located near the edge of the cap.

Phil - AC0OB
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« Reply #9 on: November 18, 2021, 09:46:10 PM »

VA3ACJ
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By the way, WELCOME! These folks have a lot of experience and are always helpful!
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VA3ACJ
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« Reply #10 on: November 19, 2021, 01:45:09 AM »

Hi Opcom, DMOD, W4AMV, KD6VXI,W7TFO,WD4DMZ,VE3BKD, and W1NB.
Sorry about my slow reply as I've been busy with work this past week. I've taken some more pictures of what I've got to work with for time being. I plan on upgrading when I get the budget to a proper monitor scope, and proper tuner for balanced line as I'm not sure that this one I'm using is the best even it say's on the back "for balance line antennas" with the jumper wire it's simply bypassing the inner choke to ground so one of my fee-lines is grounded to the tuner box. (not truly balanced) I think. I have not yet found why I can't turn up my Audio without very bad feed-back. I'm planing on re-installing the original cord & Plug with the fuse holders and caps as it may be something gone wrong with what I did there. I really enjoy finding out about the filter cap's and the difference with the x type and y type, I was not aware of this! also the tips about grounding rods and connections is encouraging to me I have to get it done before the ground freezes here, winters is on it's way, I went to the Local Home Depot and they were out of the copper pipes I was going to buy so I'll have to try another location. Thanks again for the advice everyone.


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VA3ACJ
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« Reply #11 on: November 19, 2021, 02:00:03 AM »

Here is a picture of the 600 Ohm feed line I've made going from my window to the back of the Antenna tuner, I'm concerned that I may be getting RF off of it into the room and into the gear so I've thought of this cleaver way of shielding it until it reaches outside the window area where it will then go back to being a single wire. I've drawn it up and will post the picture of what I had in mind. Basically it's taking two equal lengths of 50 Ohm coax and using the core to extend the ladder line, tie off the inside shields to the ground of the tuner and on the outside keep the shields open to air/floating. So it should act as a faraday cage and help reduce the RF inside right? What do you think is it worth the effort or will it mess up the tuning capacitance of the feed line?


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DMOD
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« Reply #12 on: November 19, 2021, 09:18:28 PM »

Here is a picture of the 600 Ohm feed line I've made going from my window to the back of the Antenna tuner, I'm concerned that I may be getting RF off of it into the room and into the gear so I've thought of this cleaver way of shielding it until it reaches outside the window area where it will then go back to being a single wire. I've drawn it up and will post the picture of what I had in mind. Basically it's taking two equal lengths of 50 Ohm coax and using the core to extend the ladder line, tie off the inside shields to the ground of the tuner and on the outside keep the shields open to air/floating. So it should act as a faraday cage and help reduce the RF inside right? What do you think is it worth the effort or will it mess up the tuning capacitance of the feed line?

You're going to have about 46pf of shunt capacitance and 0.16uH of series inductance.

Unless your balanced tuner can tune out those reactances I would say the tuning would be affected.


Phil - AC0OB
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VA3ACJ
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« Reply #13 on: November 19, 2021, 10:08:18 PM »

OK DMOD, I was thinking on that similar line. How close to those wires should the radio equipment be and perhaps an even better question may be how close should the station operator be sitting in relation to those feed-line wires? I read in a book one time that the safe distance to sit for a transformer power supply unit is about three feed as to avoid EMF radiation and this is just a simple 13.8VDC power supply with a 120VAC transformer. I'm aware that the HF signals pass threw the Human body due to the wavelength. In the past I've always used 50 Ohm co-ax that's shielded so it's never been a concern of mine. This is the first time I've tried using my home made 115 foot long ladder line, I'm really enjoying the receive compared to the old run of co-ax I've had in the past. I'm doing my best to not have any baluns or anything that will cause losses in the line as that's been my number one problem in the past. I'm also looking for ways to make my own true balanced tuner with a few coils I have laying around and capacitors. Here is a shell of a tuner that I'm planing to modify, what would you do if it was your project? I was thinking to add a SWR meter, new coil that will balance the antenna correctly somehow with taps and switch on front for the taps, outer coil with maybe 2 or 3 turns around the longer smaller tapped coil that will feed the antenna. Dose that seem workable? I've attached a picture of an internet find that I hope I can replicate in the tuner box that I've also attached a picture of. If you have any schematics as to how to add the meter in or tips about this project that would be great.


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W4AMV
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« Reply #14 on: November 19, 2021, 10:18:08 PM »

Take a look at Tom, K1JJ tuner on this site. Just enter into the search bar, K1JJ tuner.

That should be the ticket solve your issues.

Alan
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« Reply #15 on: November 21, 2021, 10:47:02 AM »

The scope has a 4Mhz bandwidth and this model is very compact, making it hard to get to the deflection plates and also add the small network to get high frequencies to the plates yet block them from being fed tnto the deflection amplifiers, while allowing DC voltage from the deflection amplifiers to get to the deflection plates for spot positioning in the usual manner. So, it is fine as a servicing scope for audio and signals up to 4MHz but not a good candidate for a monitor scope above 4Mhz, whether by mods or otherwise.

A purpose-made monitor scope would be worth waiting for, unless you have the inclination to do mods on a scope and can find a simple, more roomy, and probably tube-type scope to modify. But that's another story.

---
What stands out is that you have said one side of the feed line is connected to the tuner ground/chassis. This can be a great source of feedback and other troubles. Can you try an external current balun connected to one of the coaxial outputs on the tuner? Then no side of the feed line will be getting its RF from the tuner chassis. That chassis has to be grounded.


On the shielding of the wires from the tuner, it seems to be a really short length. I have been using a 3 FT coaxial cable from my tuner to a 1:1 or 2:1 curent balun, hung the balun from the overhead, then run about 20 FT of 450 Ohm 'ladder line' straight to the wall, where it passes through in a manner like yours. The balun should have low losses unless the match is poor. I found that out by melting the plastic case containing the balun core/transformer itself when I didn't know one side of my feed like was bad. Otherwise the balun never gets hot even with the highest power.

The tuner does not seem to have any trouble with the short piece of coax, but all tuners are different.
I will comment that I had trouble with the tuner's internal 2:1 voltage balun, and I stopped using it. Therefore the antenna signal is coming out of an SO-239 on the back of the tuner, through the 3FT length of coax to reach the balun, and out from there in what I presume is a balanced manner.

Every piece of radio gear in the shack that has a ground terminal is connected by its ground/chassis together with #12 wire (additionally I use racks though that should not be a huge factor). I also took a 20 FT length of coax cable and connected its shield to the transmitter, and threw it out 'scribble-scrabble' on the floor to act as a sort of ground. I am on a rebar-reinforced concrete slab, so there is maybe something. Although you are on wood, a good grounding and shielding scheme should still prevent the feedback you are having. Has the microphone cable good quality and in good condition -since the transmitter is an old one so may be the mike cable and connections?

The only real point in all this is that I took advantage of every possible and creative means of shielding and grounding, and I use a 15 FT microphone cable and can walk around in front of the radios setup without feedback.

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VA3ACJ
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« Reply #16 on: November 23, 2021, 02:34:22 AM »

Thanks for sharing your HAM Shack Set-Up with us here. I've done more work on the Ranger and found out that it's not getting feed back after all it's something a bit different. I ruled out most if not all of the tubes as I've changed them and the problem remained, I've also carefully checked the resistors, capacitors and again all seems fine. What's happening is no matter what antenna I hook up or dummy load, after I go threw the tune up of the transmitter and have it on "Phone" when I turn the "Audio" up more than 1/4 the way it will trigger something in the transmitter to produce a low buzzing/screeching from the smaller power transformer. I've taken a video but can't figure out how to share it here. I'm going to start another post with the tittle aimed at finding out more about this. It has the D-Lab mod pcb installed for the Keying. I wonder if there is something going on there? No mic connected and getting the same results.

Thank you all again for your advice and looking forward to updates as they happen.

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