RF Sampler For Hermes Lite

[gareth]

Hi everyone im looking to use pure signal with the hermes lite 2 and my amplifier at present is an RM Italy KL505 used on 10 and 11 meters only and max output of 250 watts. I have looked at this rf sampler and need to no if it is suitable for my needs, eventually maybe get a better amplifier but max output would be 400-500watts.  HF RF sampler (omni-rf.com)

Now i emailed the man about the sampler but he is not familiar with the Hermes.  Below is an email response from him but im out of my depth to answer. 

"I'm not familiar with the Hermes 2 but I assume that you have carried out a mod to enable it to use Pure Signal? If so, do you know what input level you need to give the pure signal input? I do have an RF sampler that could be used but it all depends on that magic input level you need. When placed after your final PA my -50dB sampler will give you a clean, sampled output at -50dB retaliative to the input power so if you're putting 500W in, the sample output will be roughly 7dBm. I may be able to create a custom sampler level depending on what you need."

So looking some advise on what he is asking or if its fine to go with his stock sampler linked above. Im in the UK and would like to order from the uk.

Thanks in advance.

[GM8JCF]

Hi Gareth

I use a -50dB RF Sampler https://symkrilag.uk/shop/rf-couplers/rf-tap-attenuator/500w-50db-rf-sampler-tap-attenuator/  only GBP 34.00 together with 2W SMA RF attenuators, https://www.ebay.co.uk/itm/404720474656?var=674718146662 around 3 for £12.  I have a selection of these SMA RF attenuators, and found that with my BLA-350Plus putting out 125W PEP, I only needed 6dB of attenuation and get very reliable PS operation.

Hope this helps

Peter - GM8JCF

[Colin Larsen]

https://oshpark.com/shared_projects/5RHcs2HH

https://www.qrz.com/db/W9AC/

Search for RF sampler down the page 

73

Colin

ZL2FL

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[G4ZAL]

I made my own by basically copying Didier's switchable coupler...

https://f5npv.wordpress.com/pure-signal-rf-sampler/

Nigel
G4ZAL

[DL1YCF]

There is one thing to note about the sampler for the HL2:

The main and auxiliary RF input are just tied together, so

a sampler with a „correct“ 50 ohm impedance will induce

a 3 dB damping of the normal input signal.

Therefore it is better to have a final pi-stage of the

sampler that has a higher output impedance (that is,

the resistor from RF3 to ground is larger than 50 ohm).

To view this discussion on the web visit https://groups.google.com/d/msgid/hermes-lite/6f1ebbd3-6985-4302-b507-576a14935f93n%40googlegroups.com.

[Frank Johnson]

In this design:

https://f5npv.wordpress.com/pure-signal-rf-sampler/

The author has made the mistake of earthing the braid at both ends of the sampling line.

It should be earthed at one end only so the braid acts as a Faraday shield.

His will sample the current on the OUTSIDE of the line and give unpredictable results.

Frank

[V85NPV]

Hello ,

i guess some alternative design maybe available and will also work.

According the design i am using it works perfectly using Thetis or PIHPSDR . One side of the coaxial Braid is NOT connected to the Ground/earth directely but connected to a 50Ohms Resistor . i have tried few but since this one is working decently and i can run this coupler after my Power Amplifier which is about 600w Max . If you are using more power just adjust one of the resistor linked to the rotary switch. This coupler is connected to my System for years now.

Best 73s Didier V85NPV

[Frank, G0GSR]

DL1YCF wrote:

"The main and auxiliary RF input are just tied together, so

a sampler with a „correct“ 50 ohm impedance will induce

a 3 dB damping of the normal input signal.

Therefore it is better to have a final pi-stage of the

sampler that has a higher output impedance (that is,

the resistor from RF3 to ground is larger than 50 ohm)."

With this in mind, I built a coupler with 1k output impedance but PS was unstable and constantly hunting.

Fitting a 3dB 50 Ohm attenuator on the PS input cured the problem.

It seems that the PS input impedance varies with input level.

I modified my coupler to have a 470 Ohm output impedance and that works OK.

If you are making a coupler, to avoid loading the RX input, it should have an output impedance >50 Ohms, just don't go too high like I did :-)

Frank

[Frank, G0GSR]

"I modified my coupler to have a 470 Ohm output impedance and that works OK"

My apologies, it does NOT work with 470 Ohms source impedance. PS still goes unstable.

The PS input seems to need a low source impedance to be stable.

We must just accept any loss to the RX signal.

Frank

["Christoph v. Wüllen"]

I am convinced that the only "clean" way of routing
the feedback signal involves
switchable parts (relays). In principle you need to
two of them:

relay #1 disconnects the feedback from the RX input when RXing
and connects the feedback to the RX input when TXing

relay #2 connects the "radio rx side" of the T/R relay with
the RX input when RXing and grounds this when TXing
(or simply does the grounding when TXing).

The HL2 IO-board has the hardware to fulfill the task of relay#1,
but relay #2 is not there in the HL2 (as in many other radios),
it takes care
that no cross-talk from the T/R relay is mixed with the feedback.
This
matters if the feedback comes from an external PA and thus should not
be mixed with what comes out of the HL2 PA (PURESIGNAL is based
on the assumption that it "sees" the signal at the antenna).

The stronger the feedback input signal, the less important is
relay #2, so feedback signals of -10 dBm (or even slightly more)
are desirable, as long as the input attenuator (down to -12 dB)
can handle this. For strong feedback signals, mixing with the
cross-talk is of course less severe than for weak feedback
signals that even need amplification in the RF preamp.

[Chuck Marzahn]

The way I'm going is a bit different.  I have the Neptune 100 coming out of Ukraine (60dbm).  I have the HL2+ with the Pure Signal input.  My intention is to put the RF sampler that you find on YouTube by Tony Albus after the Amp and feeding back with a 40 dB RF tap to clean up the signal.  Tony's 3-way isn't a challenging build and also pulls frequency as well with a variable pot as an option for the RF tap.  Oh... and it has a built in 100W dummy load.  I built a bigger resistor in for the dummy load than Tony shows.  You can find it at https://www.youtube.com/watch?v=NNKw5DLtSlU

Chuck

KQ4MHD

[Luca EA8DJR]

Hi all,

always i see talking about resistive rf tap or directional couplers.

I am using a variable capacitive coupler from Microlab HY series giving one range of 20 to 60 db variable attenuation. 

I bought NOS several years ago for some dollar on  Ebay. Is rated for high power and up to 12 ghz.

Anyone can tell me if my solution have some pro/con ?

Thank you in advance

Luca

EA8DJR