How does SDRplay hold up in city enviornments?

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WA2SQQ
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Joined: Mon Oct 03, 2016 6:36 pm

How does SDRplay hold up in city enviornments?

Postby WA2SQQ » Mon Oct 03, 2016 6:45 pm

I'm ure this question has been asked, many times, but in consideration of the latest improvements I'd like to ask again.
I currently own a Flex 6500 SDR radio. I'm not expecting the SDRplay to be as good.

I live in a relatively high RF area, about 2 km from a 50KW broadcast station on 770 khz. I'm told the SDRplay has band pass filters, but I'm not sure they would be adequate. I'm also seeing numerous comments about poor sensitivity when an efficient antenna is used, if some sort of external band pass filter is not used ahead of the SDRplay.

How well is the SDRplay doing in "city environments" where we have an above average mix of BCB/VHF/UHF RF activity?
What if any external band pass filters are people using - I know many are available on EBAY.

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dsalomon
Posts: 51
Joined: Sat Oct 10, 2015 1:50 pm

Re: How does SDRplay hold up in city enviornments?

Postby dsalomon » Tue Oct 04, 2016 12:44 pm

The filters in the RSP are definitely inadequate in a strong RF environment, especially those strong FM transmitters. I have one close to me as well. You need your own, good bandpass filtering in front of it. Re: the Flex-6500, I don't know the specs on its receiver, but I would also assume that it's significantly better than the RSP. For one thing, It has a 16-bit DDC processor, where the RSP is only 12-bit. The difference is SIGNIFICANTLY better dynamic range. Read some material on SDR basics and the value of the number of bits the DDC processor samples. Look at other SDRs with 16-bit DDCs - they all cost significantly more than the RSP. However, the RSP does what it advertises to do very well. I have several 16-bit SDRs and they receive significantly better, but I still use my RSP all the time.

There are several places to get good bandpass filters. One is from SV1AFN. His are a single board kit with switchable HF filters (one filter per HF band). If I remember correctly, they're around $80 USD. Also, you have to make your own switch box with his. There's also a company, Janilabs, that's advertising a similar bandpass filter board for less, around $55 (I think....don't quote me on that, check yourself). I have never tried those, so I can't vouch for their quality. All the inexpensive bandpass filters I've seen, SV12AFNs and Janilabs have a fairly soft passband curve, so they're not going to be as good as single bandpass filters that cost 2x-3x more (e.g. from DX Engineering, etc.) However, in the long run you should be very satisfied putting any bandpass filtering in front of the RSP, even ones that are not very sharp and don't cut signals outside the band as much as more expensive ones. Just the fact that you are lowering the overall signal level should give you better SNR, and less issues the RSP is prone to (as with ALL inexpensive, 12-bit SDRs), like ghosting.

You're probably not going to take your Flex-6500 out in the field, so that's a good use for the RSP. When you're at home, why would you use the RSP instead of the Flex? You'll get better results. Finally, don't expect miracles from bandpass filters. They won't turn a 12-bit SDR into a 16-bit SDR (i.e. they won't give you Flex-6500 receive performance from your RSP), but they should make a noticeable difference.

Here are some resources for info about bandpass filters:

https://wv0h.blogspot.com/2015/01/w3nqn-filters.html (this has a link to a QST, June 1988 article about W3NQN filters - worth a read)
https://www.arraysolutions.com/index.ph ... e_=filters (Array Solutions bandpass filters, really good bandpass filters, but really expensive as well)
https://www.arraysolutions.com/w3nqn-filters-info (another page from Array Solutions - info about W3NQN filters)
http://www.k8gu.com/?page_id=531 (another reference for W3NQN filters, with a link to a good comparison of various filters)
http://www.arrl.org/reviews-listed-by-manufacturer (ARRL page with links to some of their published material on bandpass filters)

It's also not too terribly difficult to build your own bandpass filters, it's just time consuming due to winding all those toroids. Google "w3nqn bandpass filters" and you'll find lots of good info, including some pages with info on how to build your own.

Enjoy!

73 - David, AG4F

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WA2SQQ
Posts: 5
Joined: Mon Oct 03, 2016 6:36 pm

Re: How does SDRplay hold up in city enviornments?

Postby WA2SQQ » Tue Oct 04, 2016 12:54 pm

Thanks so much for the detailed response. My 6500 is an incredible receiver. Even living so close to a 50KW station, I can listen below the BCB without any problems. Above BCB, again, absolutely no problems. However, it is a $5000 radio! I wanted the SDRplay mainly for listening above 60 mhz, to make use of the panadapter.

I saw some video on YouTube showing some pretty decent performance, but after researching each one I find out that these individuals are in rather rural areas. Think I'll pass and see what come out in a few months. No argument though, SDRplay is a lot of receiver for the money!
Last edited by WA2SQQ on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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dsalomon
Posts: 51
Joined: Sat Oct 10, 2015 1:50 pm

Re: How does SDRplay hold up in city enviornments?

Postby dsalomon » Thu Oct 06, 2016 12:55 pm

Either get some good bandpass filters or get a better SDR with them built in. The NetSDR+ from RFSpace is the BEST SDR receiver I've ever heard. I have one. It has built in filters and a 16-bit DDC, but it's expensive ($1400). The G33DDC (WinRadio Excalibur) is every bit as good as the NetSDR (I have one of those too). It is also a 16-bit receiver with built in bandpass filters. But they're not sold new anymore, you'd have to find one second hand. The FDM-S2 costs about a third of the other two. It's 14-bits but has no built in filters, so you'll probably still suffer from overload. Somewhere in the middle are receivers like the QS1R and the Perseus, both 16-bit receivers. The QS1R does not have filters. The Perseus does. I think they're both around $1000. The guys making these 16-bit SDRs with filtering are catering to a high end market and trying to compete against the best multiple conversion type receivers in the world, which they have accomplished, I'm sure that's part of the reason they're priced the way they are, even though the cost to build (i.e. component count, small boards and paying for the pick and place / soldering) is much lower.

If you're plagued ONLY by this one close FM station, then forget the bandpass filters and just buy a FM broadcast filter. It will cost less (much less) and probably fix your problem. Obviously, if you want to listen to broadcast FM, you'll have to take it out of line There is not any available that I'm aware of that can be switched in/out, You either need to build your own switching or just remove it when not needed. If you also have issues with strong paging transmitters, then bandpass filters might be your only solution. You could also try an adjustable attenuator, cutting the level of ALL the signals so your front end is not being overloaded. The problem with an attenuator, is you may be attenuating small signals out completely. So, if you like to chase small signals, that is not a good solution for you.

Good luck - David

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WA2SQQ
Posts: 5
Joined: Mon Oct 03, 2016 6:36 pm

Re: How does SDRplay hold up in city enviornments?

Postby WA2SQQ » Tue Oct 18, 2016 5:18 pm

So I received my SDRplay and I'm quite surprised. The local BCB station on 770 khz (50 kw 1.5 km away) does not seem t be having any major impact on the SDRplay. I find that the plastic case, which offer no shielding, is more of an issue. I've already started to place it within a shielded enclosure. Also, as I expected, it's nowhere near the performance of my Flex 6500 which is a $3500 transceiver.

Given the low cost, small size and extremely flexible interfacing to 3rd party software the SDRplay is definitely a keeper for me.

WA2SQQ, Bob
Last edited by WA2SQQ on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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