Wide band Antenna filters

[Fred Salles]

Hi,

Are you using antenna filters on a regular basis? 

Whether on board of active antennas or as part of an in-line booster (for the RX of course).

I actually never had to use any, using mostly passive antennas with occasionally the gain booster included in the SL6 but now that I am about to buy very wide band Wisycom tx&rx (namely MPR54 and MTP60) and I need to buy antennas I am wondering if I should get some. Wisycom makes both passive and active antennas with on board filter, but they also make the BFA booster with filters so I am thinking to rather buy a set  of passive ones (2 omni and 2 directional) and if needed I will get 2 BFA. 

Any advise welcome.

thanks

[henrimic]

If I am not wrong, the MCR54 comes already with a 32 MHz bandpass filter. That’s why, even if the frequency range is very broad, your 4 receivers needs to be tuned within this 32 MHz window. 

[Fred Salles]

Well, I am not familiar with the exact use of filters for the antenna, but I am just assuming that they will prevent overload on the receiver. I suppose just like we use low cut at 60hz for example to avoid a loud 40hz to overload the preamp even if we cannot really hear it. If my tx are set in the 800Mhz range and a very strong signal from a nearby industrial area is around 1ghz the filter on the antenna would prevent  the receiver to overload before its internal filter. Does that make sense? 

Anyone more familiar with these please correct me.

[BAB414]

Just note: Filters are different from attenuators. Both are handy to have. I use filters from a company called Professional Wireless Systems that go from 470 to 608 MHz I believe.

[Constantin]

The Wisycom BFAs are excellent to have, I highly recommend them. You have a whole range of filter settings and wide range of signal boost and attenuation from -12 to +27dB in 1dB steps. Pricey but worth it. If you are getting new antennas anyway, I would get the Wisys with the BFA integrated, or get the BFA separately for more flexibility  

[Fred Salles]

1 hour ago, Constantin said:

The Wisycom BFAs are excellent to have, I highly recommend them. You have a whole range of filter settings and wide range of signal boost and attenuation from -12 to +27dB in 1dB steps. Pricey but worth it. If you are getting new antennas anyway, I would get the Wisys with the BFA integrated, or get the BFA separately for more flexibility  

Thanks for your input. Can you confirm that I would need 2 BFA ?

Yep pricey indeed, listed 900euros each excl.VAT!! But the LFA are 1100e each (=directive active+onboard BFA) and the LBN (passive) 310e, that's 1210e BFA+LBN and I can also get the omnis passive as well so that it is more interesting in the end.

Could you also give us an idea of how often you need to use the filter section of the BFA with a significant improvement ? 

[Constantin]

Yes, you do need two, one for each receiver antenna. 
I have them always in my signal chain and they are always on and set to a fairly broadband filter, I think it’s 530-698,  but I can verfiy later. That covers all my receivers and keeps Walkie interference out, which was my main issue. Since there are always walkies on sets and I never suffer interference from them anymore, this was a great improvement.
I change the filter settings rarely, like maybe once every 4 to 6 weeks, if there are issues, and will change back on the next location. I change gain/attenuation more often, but I‘m mostly happy with a 0dB setting, or a -3 when I‘m close to the set. 
 

 

[Fred Salles]

5 hours ago, Constantin said:

I have them always in my signal chain and they are always on and set to a fairly broadband filter, I think it’s 530-698,  but I can verfiy later. That covers all my receivers and keeps Walkie interference out, which was my main issue. Since there are always walkies on sets and I never suffer interference from them anymore, this was a great improvement.

Thanks Constantin, very valuable info!

Since I never had massive problem other than very occasionally without filters I never thought of hiring them before. Maybe these occasional ones could have been avoided!

 

On 3/24/2022 at 3:50 PM, BAB414 said:

I use filters from a company called Professional Wireless Systems that go from 470 to 608 MHz I believe.

Thanks BaB. these are fixed filter like this one, right?  https://www.professionalwireless.com/product/pws-in-line-bandpass-filter-uhf-470-616-mhz/

Do you also always have them on like Constantin?

[Constantin]

22 hours ago, Fred Salles said:

Maybe these occasional ones could have been avoided!

 
In my opinion, you never know when RF issues are going to hit you. So having the filter on at all times should be SOP. There’s no downside to that, afaik

[BAB414]

On 3/25/2022 at 9:00 AM, Fred Salles said:

Thanks Constantin, very valuable info!

Since I never had massive problem other than very occasionally without filters I never thought of hiring them before. Maybe these occasional ones could have been avoided!

 

Thanks BaB. these are fixed filter like this one, right?  https://www.professionalwireless.com/product/pws-in-line-bandpass-filter-uhf-470-616-mhz/

Do you also always have them on like Constantin?

These are fixed and are always in line in my signal chain. Note that they introduce 1dB of loss if I remember correctly. The company makes them in different flavors for different bands.

[Ben B]

On 3/24/2022 at 1:50 PM, BAB414 said:

Just note: Filters are different from attenuators. Both are handy to have. I use filters from a company called Professional Wireless Systems that go from 470 to 608 MHz I believe.

I am also using these Professional Wireless System filters. I have the 470 - 616 MHz. I have them on both my cart and in my small bag. They are helpful keeping my IFB (they are in the mid 600 MHz) to overload my Rx as they are pretty close to each other.

The Wisycom BFA is of course the deluxe version which i might get one day.

[Fred Salles]

@Constantin Do you remote control your BFA from the SL2? 

I saw the SL2 allow to remote control the Wysicom LFA so I figure  (and hope) it could also work with the BFA...

Thanks

[Constantin]

No, I did not try that. My SL-2 sits in my bag, but the BFA are on my cart. 

[cjh]

On 4/10/2022 at 5:44 AM, Constantin said:

No, I did not try that. My SL-2 sits in my bag, but the BFA are on my cart. 

I think I'm going to get a pair of wisycom BFA also. Noted above you have them at your cart and not at the antenna end, I've read that they are most effective at the antenna end? Not sure why that is exactly as having them at the cart end would also mitigate any spurious RF picked up by the coax run. I'll prob run them at the antenna as have BPF at cart end already, as with you the gain / negative gain is what I will use most. There are various brands who make similar units but the wisycom seems to tick more boxes, can you confirm it has passive pass thru when antenna not powered, I think it does but it's not 100% clear in the manual.

 

Thanks, 

Chris.

[rich]

you need the amplification at the antenna end.

the idea is to add enough amplification to compensate for the loss of your cable run.
if you have the amp at the antenna, your signal to noise should be roughly the same (assuming the amplification is adding minimal noise) as if you have the receivers connected to the antennas with no gain and a short cable run.

if you have the amp at the receiver end, you are then amplifying the signal back up to where it should be before the cable loss, but you are also increasing the noise floor which is now much closer to the signal because of the loss of the coax cable.

basically, if you have the amp at the receiver end of your coax cable, you are sacrificing your signal to noise ratio.

many antennas with built in amps (wisy LFA, Audio wireless) also have filtering that is before the amp, so that any unwanted signals are not amplified which can cause additional intermod problems, and in theory, should give better results  that amplified antennas without filtering. 

[Constantin]

I have the amp/filter combo at the receiver end, because it’s simply much easier for me to mount there. Yes, it would be better to have it at the antenna end, and the Wisy antennas with the amp and filter would be even better, but I don’t need them as the rig as it is now is working fine. I only use very little if any amplification as my cables are only 3m long. I use the units mostly for filtering and for the very rarely occurring situation where I do have to use long cables. I do however sometimes use the negative gain when I‘m fairly close to the set. 
all in all, it may not be the ideal setup as it is now, but it works incredibly well and rf troubles are basically a non-issue for me

[Conor]

Be careful with amplification, use only if needed and always calculate cable loss first to know what you're aiming for. Receiver front ends can sustain damage easily if overloaded. I've witnessed an operator knock out two DCR822s by plugging in two Wisycom ADFAs into their distro that were erroneously set to +12dB, in front of a table of active transmitters set to 100mW.

[borjam]

On 9/19/2024 at 1:03 AM, cjh said:

I think I'm going to get a pair of wisycom BFA also. Noted above you have them at your cart and not at the antenna end, I've read that they are most effective at the antenna end?

If the antenna is passive the difference is minimum unless something was badly matched.

 

If the antenna is active, especially if the amplifier is broadband, putting a filter at the output is a bad idea. A strong unwanted signal amplified by the antenna preamp will be rejected by the filter, which means it will be "bounced back" and that can cause issues with the antenna amplifier.

 

Remember, except for some specialized filters that actually dissipate unwanted energy as heat, filter rejection means backwards reflection.

 

[Constantin]

4 hours ago, borjam said:

A strong unwanted signal amplified by the antenna preamp will be rejected by the filter, which means it will be "bounced back"

That is quite interesting, I never really thought about what happens to a rejected signal. 
 

With the BFA it’s slightly different, though, as it is both an amp and a tunable filter in one unit. I’m not sure it it even passes bias power for use with active antennas, but even if it did, I think using this with active antennas really won’t make a lot of sense.