power output question about the sd1446

[221Big D]

Ok got some results. I didn't get very far before seeing a issue.

Radio to meter then antenna
Ch.1 1.2swr
Ch.20 1.1swr
Ch.40 1.1swr (maybe less needle barely move)

Radio to meter then amp and antenna
Ch.1 2.8swr
Ch.20 2.7swr
Ch.40 2.8swr

I checked transistors temp after testing swr and both were just barely warm

Thanks,
Big D

 

[222DBFL]

It should go radio to amp, amp to swr/power meter, then to antenna.
You seemed to have checked the system correclty the first time, but have placed the meter In the incorrect place for testing output of the amp. The swr/ power meter should be last.
So radio out to radio in on amp, antenna out on amp to transmitter in on swr/power meter, antenna port on power meter to antenna. Then retake VSWR measurements.

 

[221Big D]

222DBFL I tested it that way first before posting. Just about the same results connecting meter after the radio or amp they stay around 2.5 to 2.8 when amp is on. Raising the dead key the swr will go down some. I have tested this with a 1 to 3 watt dead key.

I have a TS amp that works fine using same setup I usually run it with a 1 watt dead key with no swr issues.

...Update for my last post....

With radio then meter and amp and antenna last
With amp off

Ch.1. 1.7SWR
Ch.20. 1.4SWR
Ch.40. 1.3SWR

Thanks,

Big D

 

[Robb]

What model of radio?
Did you have the radio peaked and tuned?
By whom?

If you get that kind of SWR with the amp off and you've had it peaked and tuned incorrectly; then it is possible that your SWR meter is accurately reading harmonic freq's being generated because that poor tuning job. Never overlook the obvious. Common fault w/many who have hacked radios.

That would be the first thing I would check when troubleshooting a problem like this. Happens often enough.

Has the 54mhz coils been spread?
If so; then push them back together so they are as close as possible to the original shape/form.
Retest.

 

[221Big D]

10-4. I have a uniden washington mb8719 pll.
Radio has been tuned by previous owner or Tech. No coil's inside look like the were spread. They installed variable dead key. Roughly 17 watts pep on AM around 20 on SSB.I did try a different radio still had high swr's. I also have a texas star amp using same setup and no swr problems. Jumper wires I use are 3 ft.

I have looked with magnification inside amp no visible problems or anything burnt. Didn't notice any cold solder joints or anything obvious.

I'm not familiar with the circuits in these amps but trying to learn at least how to get this one repaired. I can solder and test most components.

Thanks and 73s

Big D

 

[Robb]

When the amp is turned off, the relay in the amp is open so that what RF coming directly out of the radios flows through the amp unchanged. It is in 'bypass mode'. When the amp is turned on, and the mic is keyed, then the relay closes and power can now flow through the circuit board and amplify. Just had to say that first. All tests should be performed with a 50 ohm dummy load so that your results are consistent.

So, I would first check the straight flow through the amp (amp off) and see if it having a problem with that flow. Use a DVM and resistance setting to check through it. If everything is OK; then there are only a few things that cause problems. A radio with clean output should show a very low SWR in to a dummy load. The jumper cable should be of good quality and have no issues with the connectors or the cable.

Also be sure that everything is grounded with braided wire.

I say all of this because one cannot assume anything and nothing should be taken for granted when troubleshooting.

1) Radio (mic gain set to "0" and in AM mode) > SWR meter > Dummy Load > Test
2) Amp must be turned off. Connect DVM meter "+" lead to center of input PL connector on amp input, then connect the DVM "-" test lead to output PL center conductor. Probably shows "0" ohms. I like to be sure and leave no stone unturned.
3) Radio > Amp > Dummy load > test

Using an antenna is no way to test gear when searching for empirical data.
You will need a dummy load that can handle the power of whatever amp you have under test.
If you get a less than perfect SWR out of the radio; then obviously there is an issue with that radio.

 

[loosecannon]

while all input is appreciated, i am trying to get somewhere with 221Big D, and i am the one who told him to put the SWR meter before the amp.

His radio is not the problem, his amp is.

So, 221Big D, the problem is with your amp, and it's not going to be something you can fix yourself, unless you just want to tinker with it.

The input tuning of your amp needs to be either fixed or changed.
This isn't really something that the novice is going to have much luck with, because every change you make will effect something else in the amp.
You need to know the math involved, and do it before you make the changes so you have a way of quantifying them.

a lot of CB linear amps are this way, especially the mass produced cheaper ones.
they just don't take the time to get it right when they make them.

glad to hear your Texas Star works for you, and it's not surprising.
texas star has done the work to make their amps consistent.

if it were me, i'd pull the 1446's out of it, and either save them for a future project or sell them. or you could sell the amp to someone else, but they will probably encounter the same issues.

i can't really help with the tinkering on the amp because i don't have a schematic to use to tell you where to start looking.
I can tell you that changing the value of the input capacitor is a place i might start.
LC

PS- what kind of antenna are you using, and how and where is it mounted. also describe your coax situation.
I just want to make sure there isn't something else going on that i didn't see before.

 

[vkrules]

sounds like poor input tune, could be any no of things, before you go further try changing the patch cable(preferably a different length) and see what happens.

 

[vkrules]

Sorry loosecannon didn't see your post before typing

 

[loosecannon]

Sorry loosecannon didn't see your post before typing

no problem.
i was waiting to see the full picture before i suggested that, so that we are not masking a real problem with a length of coax.
valid suggestion though.
LC

 

[221Big D]

Thanks loosecannon. I'm using a imax2000 about 25ft up to base of antenna with 75ft of rg8x (gray coax). Antenna is mounted on back of house to facial board and is grounded.

You know which cap would be input cap also is it a electrolytic or ceramic?

What length jumper would you try.. I will make one up to try.

Thanks,

Big D

 

[221Big D]

Shockwave posted this earlier in this thread. Could this possibly help my swr issue?

Ah yes, the meat and potatoes of it all. To start with, add some negative feedback. You might get away with the simple .01 cap in series with a 100 ohm 2 watt or more resistor between the base and collector of each transistor. If that does not cure it move onto installing a tunedinput circuit. Break the RF fed to the input transformer and place and inductor in serieswith it. Usually 5 turns of #16 wire around a 1/2 inch form works good. Then place a 464compression cap between the input of the coil and ground. One more 464 cap between theoutput and ground. Tune the caps for minimuminput VSWR to the amp. Feel free to expand or compress the coil to reach the optimuminductance. Another trick in the arsenal isadding some low value non-inductive resistance in series with the input circuit.


Thanks,

Big D

 

[loosecannon]

hey Big D,

yes, shockwave's post is full of good info as usual.

I am still waiting before i suggest messing with the inside of the amp, but i will say that what shockwave is suggesting is exactly what i would suggest once we get to that point.

right now, i am concerned with your grounding system.
yes, this is a digression from what you want to know about, and yes, you do have one amp that does work with this set up already.

the reason i want to know about your grounding set up is because we want to make sure that your system is set up in a way that any properly working equipment can be added in line and be expected to work.

so, just so i have the full picture, would you describe your grounding set up to me?

include any station grounding, describing all lengths of ground wires, especially the one that goes from your station to an outside ground rod if you have one.

describe any lengths of wire coming from the base of your antenna to one or more ground rods, tell me how the ground rods are connected etc...

you see, improper grounding can cause very weird things to happen when running an amplifier.
your system may not notice something until you put that amp in line and raise the power levels.


just to keep things moving along, the input capacitor you would be looking for will most likely be a ceramic disc cap. probably .01 or .02uF.
you will be able to trace it from the "TX" side of the relay, as it should be the first component after the relay contacts.

go ahead and get the parts for the negative feedback circuit, as it can't hurt to add to an amp. make sure to get components with long leads.
you can also get the parts for the input tuning if you want, as these are good to have around for other projects also.

i will give you an example of what to buy:
464 trimmer cap: https://www.rfparts.com/464.html

the important part is the tuning range which is 45-280pF. you can find other trimmer caps that look similar, and have similar tuning ranges if you cant find a couple of 464's in your price range.

the wire for the air wound coil should be insulated, and needs to be solid wire. no stranded.

and just because i am thinking about it, have we confirmed that there is not already a trimmer capacitor or two inside your amp?

the more details you provide about your grounding set up the better i can help you optimize it.
LC

 

[221Big D]

Ok thanks again Shockwave.. The antenna itself isn't grounded the pipe it's connected to is. I grounded the mast on the lower 5ft using a screw into pipe and 10 gauge solid copper wire to a 4ft ground rod. Ground rod is maybe 2 ft from base of antenna mast.

The radio equipment isn't grounded. This house is old no ground in wall power receptacles.

Do I need a ground ran to my radio equipment from outside?

 

[221Big D]

I have components to do the negative feedback mod. I havent done anything inside the amp yet though. I will work on getting my equipment properly configured first.

Thanks,

Big D