linear quesion

Need some good advice but will welcome and look into any advice given....Thanks in advance to everyone who replies to this....

I have an RCI 2950 and a (approx) 500w linear. I haven't used either in approx 5 years and have recently taken them to a local CB shop to just verify they work properly.

I was told by the guy that my jumper was too long and that ONLY a 3ft jumper should be used. (I know little about this stuff and also forgot how to actually operate my RCI so will take a few days to relearn the couple basic functions that I know how to use, like changing the channel LOL!!)

Anyway, I remember being told by another guy when hooking it up in another truck 5 years ago that because I did not want my linear on the dash in plain sight and on the floor as long as my jumper was in 3ft increments IE I had a 9ft jumper that this was fine....who's right????

Do I need to have my linear on my dash??? or can I place it on the floor with a longer jumper????

Also, the ground from my linear....Is it true that the Power wire can be as long as need be but the shorter the ground the better????

And as far as antenna.....I was using a Monkey made, but I have lost it and need to replace it....can anyone (please not just preference but actually knowledge) advise me what antenna would MATCH the best with what I am using.....

Thank you again and hope to hear from someone soon as I will be heading over the road in about 2 weeks and need to get what ever I need soon...

Thanks again...

 

The length of the jumper is not very important if the amplifier is made properly and presents a correct 50 Ohm load to the CB.

I don't use a CB with an amp, but a ham radio - it is the same thing as far as the cable is concerned. My amp has a 50-52 Ohm input (measured from 1.5 to 30 MHz), and the cable is 20FT. Works perfect, but that sure is not one of those magic lengths.

Connect a SWR meter temporarily between the CB and amp, with the very shortest cables possible (1-2FT) to determine this. 1.5:1 or better is desirable. If the result is OK, then do not worry about the cable length.

From bad mis-matches between radios and amplifiers and antennas, going back decades to the tube days, come the talk of 3-ft increments and specific lengths for everything. (Some antennas today come with a specific length of wire or recommend a specific length, follow those directions if present)

If the result is 2:1 or worse, then there is an input impedance problem with the amp that needs dealt with. choices:
1.) work on the badly designed or broken amp
2.) The radio-to-amp cable length can be cut to help transform the impedance to match it up decently, but that means complicated calculations and it will vary a bit across the 40 channels.
3.)- this is where you can use the very shortest cable between the radio and amp, if you do not want to do the above.
4.) ignore it (what many people do, it'll still work just not the best).

The amp ought to be out of sight and out of mind for obvious reasons. You can find a big relay rated 100 amps and mount it near the amp. Then you could use a small toggle switch discretely mounted on the dash to turn it on for 'emergencies'.

An amp that size draws a lot of power, perhaps 70 amps. There ought to be a separate cable for the (+) and the (-) all the way to the battery.
There can also be a short as possible ground strap from the amplifier's chassis to a good cab ground if you are mounting the antenna on the cab. The cab also needs a good ground to the frame. Some will say it will cause a ground loop, but if the amp is built right (DC power negative side is not grounded to the amp's case, and only the RF ground is grounded to the amp case) and the wires to the battery are big enough, this should not cause additional issues.
It can be a 'black art' so if there's an issue, try with or without the ground strap.

If the cab is grounded well anough to the frame and to the (-) terminal of the battery, yes you can run a small 100W amp's (-) lead to cab ground, BUT this amp you describe is much larger than where that is normally a wise thing to do, especially with all the computers and other electronic crap in vehicles today. If it were only a 100W amp, sure ground the (-) to the cab ground along with the amplifier chassis ground and try it, but if it were me, any amp gets its own (+) and (-) wires to the battery. For yours, at least #6 or better #4 wire to the battery.

Antenna? anything that is a 50-ohm antenna and does not demand a specific length of cable. Specific lengths are often used to make up for oddball conditions or as part of a special antenna design. from http://www.epanorama.net/documents/wiring/cable_impedance.html: "In order for a cable's characteristic impedance to make any difference in the way the signal passes through it, the cable must be at least a large fraction of a wavelength long for the particular frequency it is carrying." 9FT is about 1/4 wavelength, so it will make a difference, 3FT is less important, and you can see why I recommended the shortest possible cables when checking with the SWR meter above.

Sorry for TMI, but your questions have no simple answer together.