what kind of filter for Angelia board

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marc
Posts: 25
Joined: Mon May 15, 2017 2:40 pm

what kind of filter for Angelia board

Postby marc » Tue May 16, 2017 6:46 pm

Hi
I’m trying to design my “next SDR” with an Angelia board (built from component level) and some aspects of the Hermes/Angelia/Orion architectures go beyond my understanding. Particularly the input frontend

Initially, every HPSDR/Hermes/Angelia and Orion MK1 was using a combination of lpf and hpf triggered by the famous “J16” in the “Hermes Control” tab. Choosing the right lpf and hpf was giving each user the ability to configure any bandwidth bpf filter.

An 8000DLE early adopter told me that this design seems to be abandoned by Apache, and RX filters are now simple and fixed bpf filters. (literature found on Apache Labs web speak about BPF too)

- With this bpf architecture, I imagine that the TX Path LPF is not in use during RX (or does-it, to enhance the upper cutoff slope of the filter ?) Am I right ?
- Is the 8000DLE Bpf topology still controlled by the software option “Hermes Ctrl”? Yes/no ? (just insane curiosity, not an important detail for my own homebrewing)
- For which reason the Alex HPF/LPF setup screen asks for a “low” and “high” frequency limit ? (in other words, why 2 frequencies when a lpf or a hpf has only one rollon or rolloff frequency ?)
- How are equipped Angelia or Orion “200D” for the RX2 path ? bpf, hpf and a lpf “synchronized” with le tx lpf, or no filter at all? Documentation is not really clear on that point, and I tried to RTFM without finding any answer. The general “block diagram” of the Apache brochure hides all these details behind an orange square marked as “anan 100D/200D only blocks”. Published schematics don’t speak about a specific filtering in the RX2 path
- Is there any technical reason (except cost & switching simplicity) to adopt a bpf topology instead of the Alex architecture ?

I hope someone will be able to understand my rotten English and my existential questions
73’
Marc f6itu
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w-u-2-o
Posts: 1497
Joined: Fri Mar 10, 2017 1:47 pm

Re: what kind of filter for Angelia board

Postby w-u-2-o » Wed May 17, 2017 2:55 am

- With this bpf architecture, I imagine that the TX Path LPF is not in use during RX (or does-it, to enhance the upper cutoff slope of the filter ?) Am I right ?
The TX LPFs are completely independent of the RX BPFs.
- Is the 8000DLE Bpf topology still controlled by the software option “Hermes Ctrl”? Yes/no ? (just insane curiosity, not an important detail for my own homebrewing)
Yes, there are bypass paths provided.
- For which reason the Alex HPF/LPF setup screen asks for a “low” and “high” frequency limit ? (in other words, why 2 frequencies when a lpf or a hpf has only one rollon or rolloff frequency ?)
These two frequencies define when that particular filter combination will be selected. With the RX tuned to any frequency between those two then the corresponding filter pair will be in line. This provides for some flexibility when using non-standard filter hardware, as indeed a homebrew radio might do.
- How are equipped Angelia or Orion “200D” for the RX2 path ? bpf, hpf and a lpf “synchronized” with le tx lpf, or no filter at all? Documentation is not really clear on that point, and I tried to RTFM without finding any answer. The general “block diagram” of the Apache brochure hides all these details behind an orange square marked as “anan 100D/200D only blocks”. Published schematics don’t speak about a specific filtering in the RX2 path
The 100D and 200D do not have any filtering at all on the RX2 path (when RX2 is assigned to ADC2). Note that the "RX2" connector on the back panel leads to ADC2. Since RX2 can be assigned to either ADC1 or ADC2 this often does cause some confusion.
- Is there any technical reason (except cost & switching simplicity) to adopt a bpf topology instead of the Alex architecture ?
Not really. It all comes down to cost. More preselector options are better and more flexible than less.

73,

Scott
marc
Posts: 25
Joined: Mon May 15, 2017 2:40 pm

Re: what kind of filter for Angelia board

Postby marc » Wed May 17, 2017 11:50 am

Thank you, Scott.
Many aspects of the architecture are crystal-clear now.
You are right, I haven't been precise enough when I was speaking about "RX2"... I meant "the second receiver path using ADC 2"... the fact that any ADC could be used is not important/significant when considering the way these input should be filtered (or not). We are just speaking about copper and relays and toroids an caps…
Anyhow, BPF or Alex filtering, i'll try to design the same kind of filter for both ADC. That means if I decide to use the Alex configuration, I'll have to build a dedicated hpf and lpf board... and that's a lot of work, simulation and VNA tests.
pbf option is far simpler but is probably not covered by the open hardware licence of the TAPR... I don't intend to mess with Abi's intellectual property.
Tnks agn and 73'

Marc f6itu
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w-u-2-o
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Re: what kind of filter for Angelia board

Postby w-u-2-o » Wed May 17, 2017 11:57 am

Marc,

Before you go building everything from scratch, you might take a look at the various offerings available from http://eb104.ru/.

Many people have used their products to build their own custom Hermes/Angelia/Orion-based radios. I myself used one of their BPF boards to build my own RX2 preselector.

73!

Scott
marc
Posts: 25
Joined: Mon May 15, 2017 2:40 pm

Re: what kind of filter for Angelia board

Postby marc » Wed May 17, 2017 7:42 pm

Yes Scott
I almost know their web site by heart :-) UA3QLC is a nice guy and a good technical person. And I’m pretty sure one day I’ll build his 1200 W SSPA with all the protection bells and whistle.
On the other hand, I've tested his diplexer filter.... could be better compared with a WB6DHW (himself inspired by WM5Z http://www.qsl.net/wm5z/qex199907.pdf ). The one I had in my hands was really badly tuned.
I must confess, I love building stuff, I hate building “kits”, and I hate more using boards ready to use, tuned and trimmed by others.
Even when a filter has been designed by "people who knows", I try to find a better design (for example my Picastar bpf RX frontend https://wiki.electrolab.fr/images/9/9b/Bpf_montes.jpg).

A ham project without learning something or "building"something (from EDA to VNA ) is not my cup of tea. Probably because I'm definitely not a real technical guy...people who have your skill have less to prove to themselves and less time to lose to reinvent the wheel. Particularly when they are spending so much time helping other hams like you do.
It’s also probably a reaction to the general “consumerism trend” that slowly kills ham radio. When most of the threads you read on a mailing list consist to compare two microphones or speak about some gadget included in the last YaeICoWood, you really need to “do” something of your own. And try to convince other hams to do the same.

Anyhow, about these filter questions, I should say that I’m living in a very quiet area from an RF point of view, lost in the middle of the French Alps. Industrial noise level is low (some electrical fences when cows are outside in the valley, 2 months per year), far away from any big broadcast station. Thus, filtering is just an option. I can only measure a very small (3 to 5 dB) variation of the noise floor with and without filter (test made with 7th order Tcheb, 80 dB average rejection https://wiki.electrolab.fr/images/7/76/ ... ndants.png ) using several SDR. I’ll probably change my mind with my Angelia, as my “best” SDR right now has only a 14 bits ADC.

Thank you for your help and advice, Scott. I’ll keep you informed if I build a dual Alex-like board of a classical bpf filter.
Tnks and 73’
Marc f6itu

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