Great setup given to me, need some help...

[T23]

Alright a guy I know gave me a Cobra 25 LTD Classic and a Palomer 225 Linear, The radio is in mint condition and the Linear is a bit beat up but works, so my problem is now I have tested both boxes and they work just great, if you are familiar with this amp you'll know it has a Pre-amp aswell and auto SSB Switching, but the power leads are too short to work with and the wires are a bit worn out and brittle, so I am going to solder in some new power leads, I tried connecting this amp and a JCPenny 6247/SSB radio up to it with a "Calrad" adjustable power supply set to 12Volts (Goes up to 15Volts) but when I key up the power meter drops to 10Volts, any ideas? What about if I use only the amp on the power supply instead of both the amp and the radio?

Also what radio wold be better to use this with? The Cobra 25LTD classic , the Cobra 89XLR Base , or the JCPenny 6247/SSB.

Note the JCPenny is the only one with SSB.

I was also thinking about using it with my base station which is a Cobra 89XLR (Made in 1977)

Thanks.

73's...

 

[Robb]

I would use 13.8/14.1v on the supply, as this is the typical voltage used in an automobile. How many amps can the supply provide? That Palomar amp will draw about 20 amps under load and the radio should draw 3 more.

I'm not quite sure what you know about radios, so let's start with a basic. You don't have an antenna; did you put a dummy load on the radio before you keyed it up? You can damage the radio without an output load. You need either an antenna or a 50 ohm 'dummy load' on a radio when keying it up - or the output final transistors can fry without it.

Welcome to the forum.
Did you pick out an antenna yet?
Personally, I would go with the SSB radio...

 

[T23]

Well I know right much about radios, I am still learning, so I ask alot of questions, I have mobile antennas but I need a base antenna, so basically I have a mobile antenna connected while I do tests, I dont have a dummy load, or a watt meter , kinda short on funds so I like to build what I can't afford. I agree with the choice of the SSB radio, even though its old I would like to shoot skip, matter of fact skip was happening while I was testing the radio at the guys house I was getting it from...

Yes I know about having some form of a load on a radio/linear while keying up, as I said I have no dummy load and I use an antenna for testing...

 

[Robb]

SWR

 

[T23]

Yes, very familiar with SWR ,IT took me forever to find one locally... Since before I got my base or my mobile mounted radios, all I had were CB walkie talkies and wasent familiar with an SWR meter until I got some "real" equipment in.



Dakota

 

[AudioShockwav]

Look on the power supply, and see if it tells you how many amps it will put out. A few questions:

Will it run the radio by itself and stay up at 12(13) volts?
Does it only drop to 10 when you add the Amp?
Do you have the equipment grounded?
How far away is the mobile antenna?
Is it mounted on a large piece of metal?
And What is you SWR reading?

One of two things is most likely happening.
1:
The power supply will not put out enough amps to run the radio and the amp and is pulling down.
2:
RF is getting back into the power supply and effecting the voltage regulator circuit causing it to drop voltage.
If it is number one, you need a larger power supply, more amps.
If it is number two, you need work on that, Lower SWR by tuning and or move that antenna away from the radio/amp/power supply and or grounding equipment and so on.
While you can run a radio off of a mobile antenna, it will not be near as effective as a base antenna mounted up and away from the ground.
If you like building stuff, do a little research on the net about building Cb antennas, they can be built rather easily.
have a look here at some novel ideas about building a home made ground plane with some.....common materials.
http://www.worldwidedx.com/cb-antennas/59608-ground-plane-contest.html

I would always go with the SSB radio, that way you have the choice of using AM, or Side Band.
Also, I am going to move this to the Cb section, and leave a link here as this is a Cb related question.
Let us know the answers to some of the above questions/comments and we can help some more.

73
Jeff

 

[T23]

My power supply is a Calnad 45-743 , It says 1.5amps on th back of it, it looks like its about 40 years old? My antenna is right close while I have been doing testing, I have only keyed up twice with the linear in line so havent tested SWR yet, I have been having some problem with wiring the power wires , ofcourse I know how to hook everything up properly but twisting wires together just seems sort of primitive, so I tried some crimp on wire fittings but those dident hold well and fell apart, as I said before my linear's power leads need to be replaced, I should be getting a new soldering iron in this week, my old one was right crappy, so I can get that done, I have a second Calnad power supply but the voltage just jumps all over the place its not stable like the other one I have, That was my original intention to use separate power supplys for both boxes, any ideas? The radio works just fine alone on the power supply, only when I add the Palomer 225 does it do that, the needle might drop just slightly not even a volt when I key up just with the radio connected.


Dakota

 

[Robb]

I'm estimating that the power supply is about 10-12 amps @ 14v. Not enough to run the linear, but would be fine to run the radio by itself. Another 25 amp power supply for the amp - or use a car battery that can be charged when not using the amp.

The antenna that you are using needs to have a piece of sheet metal attached to give the radio a usable SWR - so that damage won't occur. Much simpler still - would be to install it in your car for now - and adjust the SWR so that it is 1.5 or less for best results. Do that part first - before you try to put the amp inline.

When you get or build a base antenna, you are ready for the next step.

I hope this advice isn't redundant for you; but I like to be sure that you don't damage what you have. Take it a step at a time...

 

[loosecannon]

you need a new power supply.
1.5 amps is not enough even for the radio.

a standard CB draws about 3 amps at full modulation on AM, about the same on SSB.

you should get a power supply that provides at least 5 amps continuous for the radio.

or get a power supply that will do 30 amps continuous and you can run both the amp and radio from it.

what do you have your mobile antenna mounted to currently? and what is the SWR?
LC

 

[T23]

Well for now , I have taken the test setup apart...I'll see what info I can get on that power supply, I am going to build a base antenna from an old TV house antenna, I can use some of the metal rod arrays and the mast and also the mounting brackets, and maby a large tomato can, some PVC aswell, I'll look over some plans for antennas and see what I can come up with though, I may post some pics of my setup and the antenna later.


T23

 

[AudioShockwav]

[FONT=Arial, Helvetica, sans-serif]Calrad 45-743 Variable PS 1.5a 2.3w-18.6w
Yes, 1.5 Amps is too small, you need a bigger power supply.
I agree with the suggestion to just run it in the car for now, battery`s in the house can tun into a mess and are not real safe if not done properly, unless you use a sealed AGM/Gel cell type battery, and they tend to be a few bucks.
You can run the Mag mount on the car, then build an antenna ( I kinda like the chicken wire one myself-I voted for it), then use a longer run of coax to hook it to the radio while powering it in the car....look for a bigger power supply, and work your way up....
Have fun!

73
Jeff
[/FONT]

 

[T23]

Would there be a way to modify the power supply I got to boost the Amprage? These power supplys aren't very common around my area.




T23

 

[Robb]

Well for now , I have taken the test setup apart...I'll see what info I can get on that power supply, I am going to build a base antenna from an old TV house antenna, I can use some of the metal rod arrays and the mast and also the mounting brackets, and maybe a large tomato can, some PVC as well, I'll look over some plans for antennas and see what I can come up with though, I may post some pics of my setup and the antenna later.


T23

Nope; no way to boost the power supply amperage. The size of the transformer pretty much eliminates that possibility. Used power supplies are cheap and plentiful. $20 can buy enough power supply to run the radio; $75 can be enough to buy and run the radio and amp - if it is a 30 amp supply.

Some people make a nice 1/4 wave antenna out of 108 inches of EMT/metal electrical conduit tubing for the vertical radiator hooked to the center conductor of the coax, keeping it insulated from the masting. Then use three pieces of 108 inch conduit hooked to the shield of the coax hanging downward or outward for the group plane of the antenna. Then, the vertical conduit is shortened a 1/4 inch at a time until the SWR is right on the money...Tune the SWR while on CH 20/AM...

Quick and easy...Do it similar to this picture...You don't need the little star-shaped device on the vertical radiator - it will work quite all right without it...Moving the ground plane radials up and down with also tune the SWR...

The first antenna I ever built was just like this one - and it worked REAL WELL...
Cheap too...Cost about $15; bur that was a few years back - more like $30 if you buy the materials new.

Or - just buy this same antenna for $50 from here:
http://www.palcoelectronics.com/p1005168.aspx

 

[T23]

Thanks, I think for now I'll make building the antenna and finding the right power supply my main priority, Finding the right power supply will give me plenty of time for building the antenna, I'll keep y'all posted...


T23