Antenna input socket

Useful information regarding antennas for SDR products.
Tech_Support
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Re: Antenna input socket

Postby Tech_Support » Thu Nov 19, 2015 8:00 pm

Hello Tomboy,
The antenna connector on the RSP is a standard SMA female connector and so the standard SMA male cable shown is the correct cable (or connector) for the RSP.

Sincerely

SDRplay Tech_Support
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GWS
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Re: Antenna input socket

Postby GWS » Mon Jan 11, 2016 8:37 pm

sdrplay wrote:We at SDRplay are very aware that for sub 1 GHz the choice of connector is not ideal. We are looking at adapters such as these from RS in the UK http://uk.rs-online.com/web/p/rf-coaxia ... s/5465092/ and will report back later. Jon G4ABQ


I've ordered one of these to adapt my current HF antenna which has been using PL-259, SO-239 connectors. I've had to chop off my old PL-259 and replace it with a BNC male connector. Hopefully this will connect precariously via the SMA/BNC adaptor :roll:

It's not very satisfactory to have all that hardware sticking out the back of the SDR. It would have been much better to have a nice robust BNC connection. BNC is frequently used for RF applications up to 2 Gc/s on Kenwood receivers .. and is useable up to 4 Gc/s at a push :) .

Best wishes, :)

Graham G4EVW
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g1hbe
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Re: Antenna input socket

Postby g1hbe » Mon Jan 11, 2016 11:26 pm

You could use a SMA to 259 or BNC adaptor lead. You can get them ready made with very flexible, thin coax which reduces the strain on the connector.
IMO there was not a lot wrong with the original F-connector!
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Andy

DaveB
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Re: Antenna input socket

Postby DaveB » Wed Jan 13, 2016 8:07 pm

You can head over to cosycave.co.uk and look at the adapters they supply. Around £3.00 - £3.25 including p&p which is cheaper than uk based e-bay suppliers.

IMO the problem with an sma connector is that, if you don't use an adapter, you need a short length of adapter cable as the cables that fit sma connectors have a high rf loss compared to the likes of RG 58 or RG 59 or the double shielded satellite cable and are only suitable for inter-connection between equipmwnt

As an aside - why did the 'radio' industry end up with two standards 50 ohm and 75 ohm??

Back to the subject. I noted when I had to take the lid off my unit to find the serial number so I could register (grrrr!) that the f-connector is actually on the end of a short piece of cable and appears to be plugged into a miniature socket on the pcb. So I suppose it would be possible to buy a suitable short adapter cable with whatever you prefer on the end and fit it to the unit.

I hope tech_support will say whether my observation is correct - and if so what is the specification of the on-board socket?
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Tech_Support
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Re: Antenna input socket

Postby Tech_Support » Wed Jan 13, 2016 10:37 pm

Hello Dave,
You are quite correct. The RF connector uses a 'pigtail' cable with an IPX connector to connect to the PCB. It is possible to get pigtails with different RF connectors on.

Sincerely

SDRplay Tech_Support
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GWS
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Re: Antenna input socket

Postby GWS » Thu Jan 14, 2016 4:26 pm

Hi guys,

Thanks for your comments regarding adaptors ..

I ordered two, one to take a BNC connector, and another to take an F type connector. Then I tried them .. yeuk :(
They were flopping about on the end of the SMA socket - not helped by the SMA fixing nut being loose. I tightened this, but the job was pretty unsatisfactory.

It was sufficient to give the radio a try - and it was pretty good :D

But then I looked at it again and thought 'I can't live with this connector setup'. I'm used to venerable Trio and Kenwood equipment, still going strong using PL 259/SO 239 connectors.

So that was it - my guarantee was going to go :shock:

I decided to put the SDR into a die cast aluminium box, fitted with a proper Earth terminal, and an SO 239 socket.
When that's done, I'll make a nice wooden box to finish it off so it looks like a decent radio. :)

It's a work in progress, but coming along OK. The tricky bit is the SMA pigtail. It's so fragile it must have been installed by someone with fairy fingers. So it's interesting to see TechSupport say there are pigtals available with various connectors - where would I look for one with an SO 239 on the end ;) - that would be something to see - heavy duty socket to a IPX microlight contact plug .. :roll:

I'll comment on my SDR radio tryout in another thread .. :)

best wishes,

Graham
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GWS
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Re: Antenna input socket

Postby GWS » Fri Jan 15, 2016 7:51 pm

OK, it's gone into the die cast aluminium box - now you can drop it on the floor, kick it, hit it with a hammer or swing it by it's cables and all will be well. :D

All I have to do now is put another splash of paint on the box, and do a bit of woodwork to make a nice case for it.
I'll have to wait 'til the weather improves for that though - at the moment it's freezing out there, and there's no decent light to work by :roll:

I like nice woody cases for kit - makes it feel more homely :) Attached is one I made for an old Trio 9R59 radio.
I sold it a while back at a Manchester radio rally ..

I plugged the boxed version in, and it's working well with the PL259 aerial plug. That's good enough for me .. attached is a picture showing the aerial connector, earth terminal and the USB connection ..

best wishes, :)

Graham
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DaveB
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Re: Antenna input socket

Postby DaveB » Fri Jan 15, 2016 9:13 pm

I recently fitted an sma panel mounting socket to my Lowe HF-225 - the type that has two nuts and bolts to secure - I then purchased (from China) a short length of adapter cable - sma on one end - f-connector on the other.

There are loads of Chinese sellers doing sma plugs to so239 pigtails at good prices. I reckon sdrplay could buy a few in and a few sma plug to f-socket pigtails and offer them as an added item when ordering.

A merchant on e-bay is selling an ipx to female bulkhead connector http://www.ebay.co.uk/itm/CAVO-CABLE-U- ... SwwE5WWk2s but doesn't have many.

David
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GWS
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Re: Antenna input socket

Postby GWS » Sat Jan 16, 2016 3:46 am

Hi Dave,

Thanks for the link to the F type socket - it's still too flimsy for me :)
I looked around but couldn't find an SO239 panel mounting socket to IPX plug. Even the chinese hadn't imagined such a thing it seems :)

I forgot to include the picture of the Trio 9R59 which I put in a wooden case - made it look much nicer than a tin box I thought ..

Competition from 50 years ago ;)

best wishes, :D

Graham
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GrahamC
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Re: Antenna input socket

Postby GrahamC » Wed Jan 27, 2016 7:07 pm

Good day all,

Just ordered a SDRPlay and patiently waiting it's arrival. Having read through this thread I though I would post a couple of comments.

Someone said (an earlier post in this thread) that all SMA connectors are 50 ohm. That isn't so, there are also (at least) 75 ohm SMA connectors as there are 75 ohm BNC and Type N connectors. 75 ohm cables and connectors are far more common than many realize.

Someone mentioned the I.PX connectors. IPX connectors are also referred to as uFL or u.FL or IPEX. A search on eBay will find a number of sources of pigtails having just about another other type of connector on the other end. Some sellers will make up custom cables as well. I don't recall seeing an IPX to SO-239 however. Some GPS receivers which have external antennas will frequently have a connector on board which is an IPX.

The coax cable used with these small IPX connectors is typically RG178 and is much smaller than RG174/RG316. You will also find listings and references for these connectors using 1.13 (mm) size cable. I don't know if "fairy's" assemble these things but I manage with my big fat fingers but does require a delicate touch.

A couple of links that might be of interest to others:

https://www.adafruit.com/product/851

https://www.sparkfun.com/pages/RF_Conn_Guide.

I have a preference for F connectors in receive systems. Good quality cable is easily found and usually inexpensive. The screw on no crimp or cheap crimp on type connectors are really not that good (i.e. crap) but the use of properly installed quality compression connectors give you connections which are weather proof, robust and good for several GHz. 75 ohm cable actually has a slight advantage to 50 ohm cable in receive only service - 75 ohm cable is better (less loss) voltage wise than 50 ohm which is better (less loss) for power. Do a search for something like "why 50 ohm" or "50 ohm vs 75 ohm" .

As for SMA connectors, they are a good all round choice and good quality versions of SMA connectors are usable well into the 10's of GHz range. The inexpensive ones commonly available from Asia on eBay are OK but probably only good up to a few GHz's. Oh, and don't get the RP vs non RP mixed up, they are not the same thing. SMA-RP have the pins swapped around - the socket has the pin and the screw on plug has the hole.

BNC connectors as with SMA connectors are available in a wide range of quality or precision. Inexpensive ones will be good up to a GHz or so and the higher quality (i.e. more expensive brand names like Pasternak) can be had for ranges up to several 10's of GHz.

At the end of the day, whether the input socket is 75 ohm with a short piece of 50 ohm cable to 75 ohm or 50 ohm connector, the typical user will likely never notice any difference. As someone already stated, the input impedance to this SDRPlay will not be one or the other over it's full range of operation - could be higher, could be lower or somewhere in between.

I am glad to see that the SDRPlay v2 still have the IPX socket on board and short pigtail to the connector on the case. SMA connectors are OK but mine will have it changed out for a F connector before too long. The flexibility of the design to allow this in such an easy fashion is plus in favour of the SDRPLay.

cheers, Graham ve3gtc
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