RF Limiter has no effect

[jazzboypro]

Hello all,

Before getting to the point here's some background on my setup.

I have a 7610 connected to a myantenna OCF-8010E-3K with a myantenna RF choke inline. The antenna is directly connected to the radio and the built-in tuner does the rest.

I also have a 8600 connected to an active w6lvp loop and to a diamond discone antenna. The loop is connected to a Delta-4 coax switch and the discone is connected to a Stidsberg 4 ports multicoupler.

I also have a 9700 connected to a GP-3 antenna

All feedlines are less than 80 feet and are LMR-400

When transmitting with the 7610 (no matter the band) the 8600 picks it up no matter the band the 8600 is listening on even on the 2 meter band. It's to the point where i no longer hear what's playing on the 8600. This happens even at low power. Even at 1 watt the 8600 picks it up. The 9700 is not affected at all even if i transmit with 100W.

Until today my solution was to not use the 8600 when i use the 7610 i was afraid of damaging the 8600. That solution is effective but not practical and would like to be able to use both radios at the same time.

I decided to buy 2 RF limiters hoping it would solve or at least attenuate (no pun indented) the problem to an acceptable level. I bought 2 Stridsberg LIM-01WB that i received today. I installed one on the loop antenna connected to the 8600 and the other one on the discone connected to the 8600. In the case of the discone i bypassed the multicoupler and and connected the limiter directly to the 8600. The other limiter is between the loop amp and the coax switch so the connections looks like this:

Loop===>loop amp===>limiter===>coax switch===>8600

discone===>Limiter===>8600

Both limiters do not seem to have any effect on the issue (maybe a small amelioration on the discone). I first thought i had installed the limiters in reverse but it was not the case.

Any idea how to solve this ?

Many thanks.
73 de va2fcs

https://myantennas.com/wp/product/ocf-8010e-3k-windom/​

 

[wgbecks]

It would be helpful if you had listed or described the frequency bands in operation for each of the three radios as you may be able to make
better use of filters to prevent the receiver overload issues. Keep in mind that a limiter when driven to conduction becomes a non-linear device
that will surely produce intermodulation products and is probably not provide the best solution.

Anyway, it seems the 7610 is saturating your loop amplifier. If installing a limiter has any chance of working it would need to be inserted
between the loop antenna and the loop amplifier. There may also be common mode issues that would need to be addressed as well.

Is there any possibly that you can increase spacing (separation) between your antennas to decrease the mutual coupling between them?

 

[jazzboypro]

It would be helpful if you had listed or described the frequency bands in operation for each of the three radios as you may be able to make
better use of filters to prevent the receiver overload issues. Keep in mind that a limiter when driven to conduction becomes a non-linear device
that will surely produce intermodulation products and is probably not provide the best solution.

Anyway, it seems the 7610 is saturating your loop amplifier. If installing a limiter has any chance of working it would need to be inserted
between the loop antenna and the loop amplifier. There may also be common mode issues that would need to be addressed as well.

Is there any possibly that you can increase spacing (separation) between your antennas to decrease the mutual coupling between them?

The 7610 is doing FT8 on 6-10-12-15-20-30-40-80. The 8600 may be anywhere (HF-VHF-UHF). The 9700 is on VHF most of the time. I guess the 9700 can be taken out of the equation since it not affected at all by any of the 7610 transmissions no matter the band. Of course depending on the bands in use on each radio the problem is more or less present.

I will try it again but when i first installed the limiter for the loop i placed between the loop and the amp and if i remember correctly no signal reached the radio that's why i placed it after the amp.

Unfortunately the antennas will have to remain at their actual location.

 

[prcguy]

An RF limiter usually clamps RF to a level around 10dBm to protect receivers, LNAs, etc, from damage. It’s not intended to reduce levels to eliminate receiver or preamp overload as a 10dBm signal is whopping big for a receiver to deal with.

 

[jazzboypro]

An RF limiter usually clamps RF to a level around 10dBm to protect receivers, LNAs, etc, from damage. It’s not intended to reduce levels to eliminate receiver or preamp overload as a 10dBm signal is whopping big for a receiver to deal with.

So the problem is severe enough that the limiter has no effect ?

 

[prcguy]

So the problem is severe enough that the limiter has no effect ?

We don’t know what brand/model limiter is being used but it’s probably not the problem. Both the WA6LVP loop and the Stridsberg multicoupler have a preamp inside and they will overload and create IMD well before the limiter will clamp.

I would test with the Discone directly feeding the R8600 with no Stridsberg and see how that plays. Or temporarily put the R8600 on the GP-3 and look for problems. I suspect it will work fine. I have a R8600 here fed from various antennas and don’t recall getting any interference on VHF/UHF when on my 7610 feeding my OCF-8010E-3K. You can’t bypass the preamp in the HF loop and it will overload when that close to a 100w HF station, so it is what it is.

 

[bharvey2]

Have you tried running dummy loads on the radios instead of the antennas (and/or separating the radios) to see if the problem still occurs? Perhaps there's enough RF leakage around the radios that their proximity to each other is causing you grief. I might look at RF coming in via the radios other cables (not the antenna) Just a thought.

 

[vagrant]

@jazzboypro - There is a difference between limiters and filters.

 

[prcguy]

I see you’re using a Stridesberg limiter and those clamp around 10dBm. They are also rated up to about 3.5W before damage and cost $130. For about $100 less you can get a much better used HP/Agilent version thats rated up to 10 watts.

 

[wgbecks]

So the problem is severe enough that the limiter has no effect ?

As @prcguy pointed out, a limiter is really nothing more than a clamp that begins conduction at a finite voltage level that's intended to
protect receivers and sensitive RF devices. The RF limiters become a simple mixer diode when saturated (conducting) that will generate
a multitude of unwanted signal products form the combination of the spectra of the applied signals.

Various off the shelf filters are available to affect isolation between HF and VHF but not HF to HF. You'd virtually need bandpass or band reject
filters to achieve the required degree of isolation. This scenario plays out over and over again at Field Day sites every year! Best solution
is to separate the antennas as far apart as possible.

 

[jazzboypro]

Thanks for all the explanations/suggestions. I still have some experimenting to do but modifying the distance between the 7610 and the 8600 has made a big difference.