Higher SWR with low pass filter

[Jim444444]

Installed a low pass filter as follows Radio/Filter/SWR meter before i had the filter the SWR was 1.1 now with the filter connected its 1.4 any idea what could be the problem.

[The Collector]

I'm not techy, but 1.4 is still very respectable SWR-wise and you pgobably wouldn't notice any difference in signal unless you were 50 miles away on FM.

Perhaps the signals above 27mhz that are being filtered out are bouncing back slightly and affecting the SWR somewhat?

I'd personally now remove the SWR meter knowing your aerial is tuned nicely, as it's just something else in the way of all your power going from your radio to your aerial. Some like to leave it inline to highlight if there's an issue like a short or water ingress etc. though

[DX-Digger]

What is the spec of the low pass filter?
Your transmission impedence has changed due to the low pass filter.

If its not 1:1:1 then the LPF is not 50Ohms at your frequency of operation. Or maybe your radio is not exactly 50Ohms, (possible if its been messed with or widebanded.
Being honest as mentioned above 1.4:1 is still a good match.
So unless you really need 1.1:1 then you should be ok.

[Jim444444]

I'm not techy, but 1.4 is still very respectable SWR-wise and you pgobably wouldn't notice any difference in signal unless you were 50 miles away on FM.

Perhaps the signals above 27mhz that are being filtered out are bouncing back slightly and affecting the SWR somewhat?

I'd personally now remove the SWR meter knowing your aerial is tuned nicely, as it's just something else in the way of all your power going from your radio to your aerial. Some like to leave it inline to highlight if there's an issue like a short or water ingress etc. though

Yeah seems good everyone can hear me good locally.

[Jim444444]

What is the spec of the low pass filter?
Your transmission impedence has changed due to the low pass filter.

If its not 1:1:1 then the LPF is not 50Ohms at your frequency of operation. Or maybe your radio is not exactly 50Ohms, (possible if its been messed with or widebanded.
Being honest as mentioned above 1.4:1 is still a good match.
So unless you really need 1.1:1 then you should be ok.

The model is a R.M. 27/586 and the radio is brand new still with seals on anyway removed swr meter i'll stick with the 1.4

[bigpimp347]

many reasons as to why your SWR can increase,
obvious is an impedance bump caused by either the filter isn't 50ohms.
other reason is you coax is acting as part of the antenna ground and matching system and changing the length of coax has now altered the length of ground, so the 'antenna' has now changed length..

a reason hacks and truck shops and clueless CBers tell you to run coax in 9ft increment lengths..

[ChrisMagpie]

The model is a R.M. 27/586

I had the same issue, with the same model of filter (which cost me £15 from Truck King, back in the day, IIRC).
After some research, I hypothesised that the filter wasn't really 50 Ohms impedance, and I bought a much better low pass filter (Kenwood LF30A) which I found doesn't affect the SWR at all. It did cost four times what the RM one cost, though. If you buy cheap, you buy twice