low pass filters

hi i allways have several low pass filters for hf kenwood type there apear on ebay there cost about 15-20 pound  the only rfi has been this lap top noisy audio when on 50mhz one ferite ring i colected the old ferite cores of the back of tv tubes there are lots of help on ham sites if you are not putting out tvi/rfi dont worry unless you interfear with your next doors tv leave well alone if you have interferece on your own gear again there are lots of info on the web good luck stay safe do radio 73s paul m0kbd

.,'

Hi
As you can see from my post on low pass filters I decided to put one on regardless of whether or not I know about interference. I know I don’t in my own home but I’m certainly not going to knock on doors and ask if there’s any problems in other peoples electronics because they will blame me for it even if it’s not me.
Answer. Just put one on!
They are relatively inexpensive and hardly effects your power output so you have nothing to lose and everything to gain.
If cb radio manufacturers would put it in the box instead of saving every penny for profit it would be a done deal!

Well, regardless of actual known need, it's still a sound practice. The one I had in my CB days, which was a 30 MHz cutoff LPF had about 30dB attenuation for a 0.5dB insertion loss, and I still use the same item on my low power gear. It was a ham radio market item, bought new at a rally, that cost me a fiver vs the silly money garbage sold to the CB market back then filter wise. I eventually added one inline with every base setup CB rig (I had a dozen of various gens) pre antenna switch and a final on the antenna side, so effectively any radio had the benefit of two cascaded LPF's and minimal insertion cost.

£30 was a small price, all told, for piece of mind. But it was a sore point of making me look like, in today's vernacular, a "try hard fake" - but I was just taking responsibility for my radio usage and consequence of it by avoiding avoidable issues.

And for certain, it demonstrated just how much impact not having one fitted makes because it's not just the attenuated low harmonics and overtones that cause problems, it was the cleaning up inherent on the fundamental as well adding to the effect as often your fundamental was carrying nasties introduced by PLL and other circuits that induced into the carrier. Even on my HF ham gear, there's a cascade setup which defines my faith in the use - and given I worked a lot of SSB and CW/TG in my early ham license time before analog TV got shut down, it was pretty much essential as it was very much needed on SSB and TG even on well setup gear.

If the CB manufacturers hadn't been greedy exploiters who corner cut to the nth degree, external LPF's would have been added piece of mind as usually the case.

Mind you, some later Chinese gear and not just export and legit CB gear, had questionable LPF's internally anyhow.

A5H5ATAN1C wrote:

If the CB manufacturers hadn't been greedy exploiters who corner cut to the nth degree, external LPF's would have been added piece of mind as usually the case.

Mind you, some later Chinese gear and not just export and legit CB gear, had questionable LPF's internally anyhow.

Hi  
But also remember that CB radio was a mobile radio system that was primarily used in cars and trucks. They shouldn’t need the filters. 
 As far as I’m aware there’s no new Homebase sets with decent filter systems built in so it’s just a case of taking responsibility and doing it. 
It would cost more than £30 added to your new cb radio if it was built in anyway.

True, in the CB market there's very few of any kind with built in very high rejection LPF's - but the ones I know of weren't UK/CEPT gear and wear purpose built manpacks that predated CEPT standard stuff and were used (under specific license) as training gear before the conscripts and volunteer reservists (mid 70s era) got let loose on the pricey military gear. Mind you, they also had much better Rx side filters too. I had one here on test for repairs, and was very impressed how clean they were, and the effective cost of both lots of filters was peanuts compared to what the manufacturer stiffed the services who used them for.

But as for use of LPF's on the output side, there's actually no exception to why any application shouldn't have a suitable LPF fitted into the final chain or in the transmission feed. Where you use the gear and why, is irrelevant to why an LPF should be used. Even if your gear is super clean, it's a precaution that's worth having as much as even a plug in RCD makes sense with power.

You seen, aside from precaution as radios and their TX purity decays over time as components age and there are times when integral filters can fail in a bypass way rather than go open circuit. So having an inline retrofit internal high grade unit or a functional LPF in the feed line adds creditability to your efforts to keep your shack in order - and as any ham can tell you, if your shack ever gets scrutinized formally (all radio users are at risk of that) - evidence of actually making an effort to fit an LPF works in your favour two-fold as beyond a spot random check instance, the most likely reason for a check is following a complaint where you've been cited as the cause without evidence.

Whilst I respect my £5 high grade stuff, a quantity of them, isn't really something you'll find generally (not 500W rated surplus gear anyway), even if you end up just using one and it costs say 30UKP for 30dB rejection and 30W rated, it's a piece of mind bargain as that's a good ratio of cost vs spec and definitely over spec for Tx requirements of legally certified CB gear and all bar the very high output (40W plus) export gear and for most QRP HF ham gear fitting.

But as a counter to the argument about CB radio being primarily mobile focused and BS associated reasoning using that logic to why LPF'S aren't really needed/necessary even for precautionary purposes, I'll point out also that there was and still is 11m professional usage of mobile gear that predated CB and still is on the books as primary service use for the military and they all incorporated high rejection/attenuation LPFs internally, externally or a cascaded combination of by default even though the users were a law unto themselves when using radio gear on duty.

So like I say, there's no context really where you can legitimately argue LPF's are unnecessary/pointless and the sanity and beneficial peace of mind and residual benefits of an effective legit functional LPF that's fit for purpose brings in a huge peace of mind and is good precautionary body armour vs back-stabby bstards who fabricate interference claims against you at the level when you have to address your setup under formal assessment and rapidly goes a long way to disputing such claims when you're clearly actively employing precautionary methods to reduce out of band and allocation secondary emissions and keeping a station that minimises intentionally generated legit in-band and in-allocation RF emissions to a necessary evil level worse case, so adding to your out-of-band consequential reduction efforts notably.

If only things were that clear cut and simple in other contexts, a great many other 'to use or not' dilemmas would be easily as easily solved as to rationality vs practical application.

rabbi wrote:

hi i allways have several low pass filters for hf kenwood type there apear on ebay there cost about 15-20 pound  the only rfi has been this lap top noisy audio when on 50mhz one ferite ring i colected the old ferite cores of the back of tv tubes there are lots of help on ham sites if you are not putting out tvi/rfi dont worry unless you interfear with your next doors tv leave well alone if you have interferece on your own gear again there are lots of info on the web good luck stay safe do radio 73s paul m0kbd

Got to say Paul, I have always used LPF's and as you say either Kenwood or Comet, even and especially in the "Old days"

Just coming back to 11m after so long, realised I need one as I TX'd on 26MHz yesterday to test tuning on the long wire and got RF in the shack bad enough to start my paper shredder up  
So I think I will be looking for an LPF before utilising all 3 bands on the SS9900, may actually look for the Zetagi TVI Filter just to be fashionable 

BAREFOOT wrote:

rabbi wrote:

hi i allways have several low pass filters for hf kenwood type there apear on ebay there cost about 15-20 pound  the only rfi has been this lap top noisy audio when on 50mhz one ferite ring i colected the old ferite cores of the back of tv tubes there are lots of help on ham sites if you are not putting out tvi/rfi dont worry unless you interfear with your next doors tv leave well alone if you have interferece on your own gear again there are lots of info on the web good luck stay safe do radio 73s paul m0kbd

Got to say Paul, I have always used LPF's and as you say either Kenwood or Comet, even and especially in the "Old days"

Just coming back to 11m after so long, realised I need one as I TX'd on 26MHz yesterday to test tuning on the long wire and got RF in the shack bad enough to start my paper shredder up  
So I think I will be looking for an LPF before utilising all 3 bands on the SS9900, may actually look for the Zetagi TVI Filter just to be fashionable 

Wouldn't an RF choke help with issue better than a TVI LPF? I thought a TVI filter just suppressed transmitted harmonics, not RF coming back into the shack, or can some do both?

Hi Neal, I seem to remember, that LPF and TVI filters are similar, they are there to reduce or eliminate interference from your TX to other electrical items usually close by. I could save money by attaching a clamp on Ferrite to the power lead of my Shredder??

But You may also have reminded this old sea dog that an RF Choke close to feedpoint of Antenna might also prevent RF coming back down the Braid!! 

Thanks Neal, will dig out some Plastic pipe to wrap the coax round it, 

cheers Tony

BEARFFOOT I did exactly the same thing to make a common more choke by wrapping the coax 5 times around a 110 mm waste pipe coupling with has a raised edge and is the perfect width for those 5 turns of RG 213,just 4 cable ties to hold everything tight and into position.I think it helps.Plus every cable and lead has a clip on ferrite ring (The clam type)£10 for an assortment of 20 different sizes.The low pass filter I’ve used one of those too from RM Italy mainly to stop reflection back from the antenna on 2nd harmonics.I don’t claim to be an expert there are far more experienced and knowable members on this forum,but from what I gathered on here by just asking it had certainly helped with any QRM.Apart from the odd occasion where it might spike for a while I’ve normally just got an S3-S4 at worst.And breath sorry for the long winded story..
Cheers Tom.
26 CT 4029

BAREFOOT wrote:

Hi Neal, I seem to remember, that LPF and TVI filters are similar, they are there to reduce or eliminate interference from your TX to other electrical items usually close by. I could save money by attaching a clamp on Ferrite to the power lead of my Shredder??

But You may also have reminded this old sea dog that an RF Choke close to feedpoint of Antenna might also prevent RF coming back down the Braid!! 

Thanks Neal, will dig out some Plastic pipe to wrap the coax round it, 

cheers Tony

Sorry that was the wrong emoji that ones for the missus
Tom.(what an idiot)