Low pass filter

https://www.rxtx.fi/paavalikko/rm-35mhz-hf-low-pass-filter-24-30-mhz-alipaastosuodin-600w/p/613014/#description

Any idea if this is a good filter?

Hi Glenn,

A 9-pole Chebyshev filter is always going to be good at it's job but it depends on what 'job' you want it for. (Your FT450D has similar specs for harmonic suppression built right in.)

Is it in an attempt to reduce any RF interference you may be causing?

In which case you might find yourself disappointed as well as bereft of some cash for one. (You can build these things for a fraction of the price they charge for them!) These filters are designed to reduce any RF harmonic or 'spurious' emissions that may be emitting from your transceivers but as already mentioned your FT450 is similarly specified and your other radios won't be that far behind.

There's always the argument that running a linear amplifier will also 'amplify' any harmonics but it's highly unlikely. (Either through built in additional filtering or the fact that the amplifier can't amplify such higher frequencies it's design running out of steam well before then.) Only if it is of a poor/cheap design will it produce harmonics of its own.

Your main harmonics will be the third and less so the fifth/seventh, so for CB frequencies any main 'problem' will be just under the commercial FM broadcast frequencies (80MHz odd) so not really affecting anyone. Your fifth will be within aircraft band range but so small as to be almost impossible to cause any such interference.

The main issue with any sort of RFI is usually front-end overloading of poorly designed receiving equipment or electromagnetic pickup sometimes on equipment not designed to pick up radio frequencies at all! If that's in your own property it's not usually much of an issue but does cause problems if it's affecting a close neighbour. 

In this instance your 'expensive' filter may not actually help you at all.

If you do have problems causing neighbourly interference then it's always wise to work with them to resolve any such problems. 

Cheap 'baby-monitors' can be a concern especially for 'new-parents' who will see such interference as cause for panic and a new monitor may resolve that especially if utilising better technology on different frequencies such as UHF/Wi-Fi/Bluetooth. A gift of a new baby monitor may well be cheaper for you than a filter and short lived as babies grow quickly.

If interference is over a typical sound system then just remember that all those long wires to the speakers will act like fairly efficient antennas! A few cheap toroids/chokes will help out there.

Similarly for PIR flood lights that 'go-off' every time you transmit especially in today's cheap Chinese manufactured products.

The other option.....turn down your own transmitting power. (You might 'miss' some DX! )

If you're whacking out hundreds of Watts in all directions you're bound to affect someone close by, which is why it helps if you're out in the middle of nowhere.  

That or do some reading up on 'common-mode-chokes' if your signals are coming back down your coax.....


Apologies for my 'waffle' there Glenn, but I've been away for a little while and got some catching up to do!

All the above info given can be found in any intelligent resource. Opinions may differ when armed with a small amount of knowledge, friend-of-a-friend-of-a-friend recommendations or sometimes forum threads.

All the best,
Victor

You can buy used Kenwood, Comet and Yaesu ones rated for 1kW for £30 or so, around £45-£50 new like the Kenwood LF-30A. I'd rather trust one of those.

Hi, thanks for the info, i need it for my MK KINLEY radio, FT 450D is working well, never over 2 bars of static, just want the MK kinley working better, it is getting 7 bars of noise these days, done all the tests  no luck, only one thing that i am thinking about is , i live near a Finish Defence live practice range and these days it is very active, gone for a dog walk to the area close to the main entry gate, with my hand held President , its 9 bars of static, i did the order today for the filter, so will report back next week on what it has done, thanks Victor for the good reply an d Northern crusader, Finland is expensive  and only one true radio dealer RX TX TUOTE so my options are low for shoping naround.

I hope it all works out for you Glenn but not sure whether such a filter will help you with your reception issues. It has to be said that as good as the McKinley is for a CB it isn't a jot on what the Yaesu 450D is capable of doing simply by better design.

In a day of overly sensitive receivers it's often worth remembering to not crank everything to "11" and you'd be surprised how signals jump out when you turn the RF gain down a smidge. As good as your Yaesu is I still do this with mine (450-AT) for signal improvement and know it would benefit the McKinley.

The other issue is that you may well be comparing apples to oranges by making comparisons between different radios. I know that as an owner of multiple radios myself nowadays it's a "dangerous" game to play and best to enjoy the merits of each radio individually.

Again, I wish you well and would be pleased to hear how you get on.

73
Victor

Hello, I like using the Mk kinley more than the 450d, just something about cb radio been nostalgic for me, the new Superstar 3990 with its old fashion style and moving needle, is great, and that seems to filter out signals better than the Mk kinley, 3990 is 4 of static base line, will let you know what happens, I have 14 day return policy.

Update,  after a few weeks using this filter with my radio is seems to work better for local radio within my home location,  on Dx it took about 1 signal point of qrm off the Mk kinley radio