tune first with the amp off and out of line, then add the amp but leave it off. Lastly tune with the amp on.
+1
Checking and tuning antenna system first with just radio and antenna, with the SWR meter at the radio. And find and tune for lowest SWR between the RADIO and Antenna.
Doing that - saves you the headache of starting out with problems you have to sort out as combinations of this to that swap this with this and move this to there...all done because you didn't simply check to see if the antenna and radio will work together first.
Throwing it all together is not a good idea, One step at a time - stop check and proceed versus tweaking to get it all straightened out - Antenna to Radio first, then Amp in with it's patch cord to radio Coax from antenna to amp - then check - then try tweaks with amp on. IF you get low SWR and then it suddently jumps, stop there and solve the issue first.
This HTML site may help you if you encounter problems...
http://www.firestik.com/Instl-Text/ford174.htm
I would like to add if you have the ability to;
- get a barrel connector - two SO-239 so you can put the jumper in with the antenna join the coax together and check SWR - they can join the coax jumper to the one that goes to the antenna and if all that tied together and the SWR is still low - you solved a step and you can rest easy to continue with putting this together...
These, above, are for RG-58 or RG-8 - or 50 ohm impedance systems - like your's
Why the Barrel connector? Because - if you have a problem with the antenna, it's location or the radio doesn't seem to work well or you encounter mounting problems of if the jumper you want to use not of good quality, these quirks are going to cause a reaction or reflection in the system.
It will also help you when you need to remove the amp for service - you can just join the two cables together and continue on using the radio like normal. Like a break point. Take out amp, join cables together - life goes on.
But be careful, there are other types of connectors that fit different cable - they are also sized differently and you may already recognize them as TV or Cable-TV or 75 ohm Type - F connectors for RG-6 cable - these - DON'T use on your system for they will screw up your day...
The above is for 75 ohm Cable TV or Stereo Antenna or Arial On-Air cable systems
Then, of course, you'll have to tie it all together; and how you install it, and how well you do this task - plays a role in how many surpizes you can encounter if you didn't pay attention to the routing, connections and their quality and the amp mounting location and routing power and coax to where they need to go.
Notice there are two types of coax being connected above...
Can you spot the pre-made and recognize the hand-made one?
See the difference?
If the antenna was the issue - and you put it all together without seeing if the antenna was going to work as a unit with the radio - putting the amp in line just added 5 more problems to your 1st one.
What 5?
Amp,
Coax jumper to Amp
Amp
Coax to antenna
Radio and antenna working together with the amp inserted.
Now for most people they would usually wind up at a local radio shop to help tweak the system so it works and doesn't kill the car or the driver from the cars airbags going off from RF getting into things they shouldn't...
It's when you get a tuned system that was tuned elsewhere - using their equipment, their coax jumpers and their antenna - and all you get shipped from there, to you, is the radio, the amp and a power cord to fit the amp - you are now left with the task of putting it together correctly like they did.
That's the crux, so be careful...