Viper652
Moderated
When antenna is directly connected to the radio it's fairly high SWR. So the amplifier is automatically tuning it better?
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Low SWR when amplifier is connected to the radio
- Thread starter Viper652
- Start date
Are you checking the SWR with a meter on the antenna line or at the output of the radio? If its at the radio when the amp is on the SWR meter will read the match of the input circuit inside the amplifier which has nothing to do with the antenna. The match at the antenna will be the same no matter what the power level, unless your heating up the antenna.
Viper652
Moderated
It's with the amp being off
Viper652
Moderated
I can receive better and transmit a bit further.
Does that make sense. The SWR is way above 3 just antenna to the radio. It's between 1-1.5 with the amplifier connected
Does that make sense. The SWR is way above 3 just antenna to the radio. It's between 1-1.5 with the amplifier connected
The amplifier through path will have lengths of coax, maybe circuit board traces, relay contacts, etc. In some cases where the antenna system has an inadequate ground plane, the coax to the antenna can become part of the tuned antenna system and adding or subtracting coax length can change the match. Could get better, could get worse. I suspect that's what's going on.
If you have a 50 ohm dummy load connect that to the amplifier and check the match with the amplifier off. All the extra coax and circuitry in the through path should make the match a little worse into a dummy load and that is normal. You can also put the load right on the SWR meter or on the radio if using the internal SWR meter and that will tell you if the SWR meter is somewhat accurate if it shows a perfect match.
707ways2Sunday
Member
- Joined
- Nov 1, 2023
- Messages
- 65
Normally that won’t happen if the antenna is tuned properly. What antenna do you have.???
K
ka1bwo
Guest
High SWR at the output of transmitter can be caused by the antenna being mismatched, or coax problem. If you have a 50 ohm dummy load you can isolate the problem. If you disconnect the coax from the antenna and connect the dummy load to the end of the coax and remeasure SWR. If the measured SWR is 1:1 there is a problem with the antenna, if the SWR is still high the coax is at fault. If the antenna is at fault look for the obvious things, poor connection, broken wire or connector. You can also try to lower the SWR by adjusting the antenna length and or matching network. If none of this works a SWR measurement is scalar without the phase angle you can't determine the antenna input impedance vs frequency to understand the problem. When using an amplifier, the amplifier input impedance is 50 ohms for a low SWR.
Your amp probably has the same 50 Ohm impedance as your radio so it's kinda' fooling your SWR meter into thinking it is low. If you reconnect your radio directly to the antenna then that is the true standing wave ratio (SWR). If the SWR' high (generally 2.0:1 or greater) then you have a number of ways to lower it.
An SWR of 3:1 is high. Should be 2:1 or lower when the CB is connected directly to the antenna. Check your radio's and amp's manuals to determine the maximum SWR it can handle. Some CBs and amps can be damaged by a high SWR while others have fail-safe systems that automatically lower the radio's output when SWR is excessive. Hope this helps.
Viper652
Moderated
102 inch whip
707ways2Sunday
Member
- Joined
- Nov 1, 2023
- Messages
- 65
OK then, I will second pcrguy’s post mentioning inadequate ground plane.
