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Silverload took a dump.. Which antenna now?
- Thread starter SuperDave
- Start date
I guess the only thing Im worried about is running the whip and my TS500, because that 1.5 SWR wont be the same when I turn that amp on... correct? Theoretically it should get higher..So yeah, that's my only concern.
If your SWR goes up (or changes at all) when running an amp one of two things is happening.
1) The output of the amp is not properly tuned to match to a 50 ohm transmission line. This is the typical cause of this problem.
2) Something in the system is being pushed to or beyond its design limits.
I'm running an amp made by a local, SWR's show the same weather it is on or not.
The DB
If the amplifiers output impedance is 50 ohms, and something else isn't causing an issue due to the higher power, the SWR will be the same weather it is on or not.
SWR is a ratio. x% of the power being transmitted is being reflected by the antenna back up the coax. It doesn't matter if the input is 1 watt or 1,000,000 watts, the same percentage of power will be reflected (assuming the antenna system including the coax can handle the power of course).
The only real issue you should have is if the amplifier is being driven hard it will be much more sensitive to SWR. You may consider getting an unun if you are worried about it. That will resolve any potential SWR issue.
How do you know your antenna is at 40 ohms of impedance? Have you hooked an antenna analyzer up to it? Most quarter wave antennas are at 35 ohms of impedance.
The DB
I replaced my Wilson 5' silverload with a Firestik 5' tuneable tip. It is mounted on the passenger side of my truck, right behind the cab. Good performance and SWR's, too. The 102" whip is just not practical for me, but I know they work great. Nice truck, btw.
73,
RT307
73,
RT307
I read that the whip was around 40 ohms and I don't have the antenna yet so I don't know the exact number. I've been running the Silverload up until I started having problems.
Thanks 2RT307, 230+ thousand miles.. it's a moving work in progress.. haha
Well, I picked up a whip and spring today, but my excitement was soon ended.. my meter is still doin the same thing with my amp on. My power when keyed should be at 125, but it jumps around and falls to 50 or so. My radio checked out fine until just a few minutes ago. The amp meter lights up but the needle moves erratically just like my external meter.
The radio DKs 2 watts but now won't swing pass 5. Just earlier it was swinging 20.
These are my symptoms so far. In about an hour I'm gonna start doing some looking around again.
This wasn't what I was wanting to happen! Haha
Edit.. when I mean erratic, I mean it goes up to 125-200 then falls back down to 50 or so. Some times it will move slowly between 50 and 100 watts.
The radio DKs 2 watts but now won't swing pass 5. Just earlier it was swinging 20.
These are my symptoms so far. In about an hour I'm gonna start doing some looking around again.
This wasn't what I was wanting to happen! Haha
Edit.. when I mean erratic, I mean it goes up to 125-200 then falls back down to 50 or so. Some times it will move slowly between 50 and 100 watts.
Brake, who do you buy your coax from? I'm looking to possible order a premade 18' section of RG-8x.
Dxengineering.com any good?
U
http://www.dxengineering.com/parts/dxe-8udu018/overview/
X
http://www.dxengineering.com/parts/dxe-8xdu018/overview/
The radio is working fine now, but it is grounded to the seat frame. It seems as if the lock washer that came with the antenna mount shorted out by coming in contact with the center of the stud, but my amp is still doing the same stuff. I noticed the washer issue when I made a new mount for the whip so I could move it away from the cab.
All of my jumpers check out fine. Next thing I need to do is pull the coax out from my antenna to the cab and check it for kinks/abrasions.
I will check the ground for the amp and check my bonding straps aswell.
It just seems strange that when I key down with the amp on the meter on the amp will jump around or sometimes not move much at all. To me it seems like it would be a short in the power wire/ground.
I got my 18' run from a local shop. It's rg59. I took a 3' jumper and cut it in half an put new ends on it. It jumps from radio-small amp in dash-meter. I have the meter removed and a barrel connector in it's place. All that puts me around 21-22' in total length. Ima try to score some large coax from work. We've got some 7018 on a fairly large spool. Make a grand total of 18' from antenna to radio.
You may just have a bad spot on your coax. If you don't have a meter to check it, it's just as easy to go to RadioShak and get another 18' piece of the cheap stuff. If all the readings are normal, then get you a good piece of coax ordered. I keep a RatShack piece for trouble shooting.
You may just have a bad spot on your coax. If you don't have a meter to check it, it's just as easy to go to RadioShak and get another 18' piece of the cheap stuff. If all the readings are normal, then get you a good piece of coax ordered. I keep a RatShack piece for trouble shooting.
I've got a meter to check the coax. The continuity checks out fine, but I didn't get to pull the 18' peice out because of rain today. However I did check continuity at the pl-259s on it and all checks out good.
Also I took the cover off the amp to check voltage coming in while I keyed the radio with the amp on. My voltage never dropped below 12.20 or so. (truck was off) Unkeyed the voltage was 12.54ish.
could this still be a voltage issue? From the way it looks the amp is getting the voltage it needs.
Any helps is appreciated!
What's with this 18 foot thing, it's nonsense. There's nothing 'magical' about 18 feet of coax, and it seldom, if ever, has any meaningful use. It amounts to trying to 'tune' an antenna system with the length of feed line. The simplest/best way to do that is by tuning the antenna. Then, the length of feed line makes no difference at all. If the antenna isn't at least close to being tuned correctly then feed line length can make a difference (usually not a good one though).
Of course, it also goes back to a lack of knowledge of what SWR is and how meaningful it is/isn't. SWR deals only with impedance matching, doesn't tell you anything about how 'tuned' an antenna. To understand that you have to know what impedance is composed of, how those 'parts' of impedance affect things, what's meaningful and what isn't.
I know that isn't what you want to hear but it doesn't affect the fact that you need to know that stuff. And until you do you are wasting your time and money.
Have fun.
- 'Doc
Of course, it also goes back to a lack of knowledge of what SWR is and how meaningful it is/isn't. SWR deals only with impedance matching, doesn't tell you anything about how 'tuned' an antenna. To understand that you have to know what impedance is composed of, how those 'parts' of impedance affect things, what's meaningful and what isn't.
I know that isn't what you want to hear but it doesn't affect the fact that you need to know that stuff. And until you do you are wasting your time and money.
Have fun.
- 'Doc
I know the 18' coax thing is a myth. My longest run just so happens to be 18'. I didnt plan it that way, it just fell out the way it did.
op: Anything else to add to my Amp problem "doc"? Being that Im seing 12v when keyed down could this mean Im having an internal problem with the amp?