Coax Switch for different Bands

Forum for discussion about the Langstone Microwave Transceiver that shares some features with the Portsdown. Wiki: https://wiki.microwavers.org.uk/Langstone_Project
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DL5BCA
Posts: 64
Joined: Tue Jun 30, 2020 11:59 am

Coax Switch for different Bands

Post by DL5BCA » Tue Jun 30, 2020 12:20 pm

Hello,
i use a Pluto to work over the QO100 bird.

The Langstone TRX is a fine possebillity to work on different Microwave Bands with one TRX.

I think an important thing is to switch the transmit and receive signal from the Pluto to the corresponding preamplifier or amplifier.
Is there anything that you can switch the Pluto to 5-6 outputs?
It must work from 70MHz to 5800MHz, with as little loss as possible.

73 Tommi DL5BCA
73 Thomas
DL5BCA

g8gtz
Posts: 1287
Joined: Wed Apr 07, 2010 6:26 pm

Re: Coax Switch for different Bands

Post by g8gtz » Wed Jul 01, 2020 1:04 pm

Hi

The Langstone uses the same GPIO pinout so you can use the Portsdown 8 way RF switch up to 3GHz or some people are uses a Teledyne 6 way SMA relay which can be driven off similar logic.

https://wiki.batc.org.uk/Portsdown2019_ ... put_Switch

73
Noel - G8GTZ

g0mjw
Posts: 1272
Joined: Sat Sep 20, 2014 9:15 am

Re: Coax Switch for different Bands

Post by g0mjw » Wed Jul 01, 2020 4:32 pm

We agreed some GPIO to support 8 relays. See elsewhere in the forum. It's working well. viewtopic.php?f=129&t=6602&start=60

Mike

https://i.ebayimg.com/thumbs/images/g/L ... -l225.webp
Last edited by g0mjw on Thu Jul 02, 2020 8:05 am, edited 1 time in total.

g8gtz
Posts: 1287
Joined: Wed Apr 07, 2010 6:26 pm

Re: Coax Switch for different Bands

Post by g8gtz » Thu Jul 02, 2020 7:36 am

See this post for how someone else solved it:

viewtopic.php?t=6658&p=23449#p23449

g0mjw
Posts: 1272
Joined: Sat Sep 20, 2014 9:15 am

Re: Coax Switch for different Bands

Post by g0mjw » Thu Jul 02, 2020 8:34 am

That would work, as would one of the common 6 way SMA switches that nobody wanted a few years back. Very useful, now the prices are rising. Another alternative is to use a combination of relays and diplexing filters. Bear in mind you will need a filter anyway. It's difficult to make a 6 way diplexer but it's possible to make two triplexers and switch between them with a normal coax relay. At these frequencies, lots of relays in parallel doesn't work well, even with the microwave PCB relays.

One way to overcome the high cost of new pukka RF SMA relays is to use PCB relays. You can and I have tried a cascade chain of 1->2 makes a decent 4 way switch and adding extra relays gives more outputs but the losses can be high, especially on FR4. That might not matter though if some additional gain stages were included, it's low power. We are not after ultimate isolation, just separating the various bands and there are tricks you use to minimise the number of stages used on higher bands at the expense of the lower ones where it's less critical.

The AXICOM relays might be a good choice https://www.digikey.co.uk/products/en?FV=-5|6210 Digikey part number PB1103CT-ND is a SPST RF relay rated to 3 GHz for £15. It will probably work at 6 GHz for this application. Part no Z6091CT-ND is a G6K RF rated relay DPDT also rated to 3 GHz and could switch and costs £20. Whatever, but with several relays required the surplus 6 way SMA relays are going to start to look like better value. It's a pity the switching ICs seem so poor and fragile.

A simple RF switch plus filters PCB could be designed and acquired from the usual Chinese PCB manufacturers. Probably good enough if you use the 0.8mm board and pay attention to layout.

Mike

g4eml
Posts: 252
Joined: Thu Apr 26, 2018 9:36 am

Re: Coax Switch for different Bands

Post by g4eml » Thu Jul 02, 2020 9:54 am

The TE Axicom brand HF3 PCB mount relays are specified to 3 GHz at 50W and seem to work well. R.S and Farnell stock them in the U.K. at varying prices, the cheapest I found was £6 for the type with 4.5V coils. Easy enough to add a series resistor for 12V use.

They also make a HF6 type with a 6GHz spec. That appears to be the same relay but encased in a metal jacket.

g0mjw
Posts: 1272
Joined: Sat Sep 20, 2014 9:15 am

Re: Coax Switch for different Bands

Post by g0mjw » Thu Jul 02, 2020 11:31 am

I have just had an off the wall idea. How about a modamp (16-20 dB gain thereabouts) followed by a restive 6 way power splitter on the TX side. That should give the TX outputs - mini-circuits do a range but they quite expensive so just make one from resistors either as cascaded 2/3 way or star configuration. The 6 GHz is the real challenge here. There are mmics too e.g. SRSC-4-63+ but too costly.

On the RX side, 6 individual modamps and a 6 way resistive combiner. Power to the modamps switched per band. Resistive splitters have very little isolation but an off modamp has at least 10 dB loss and and on one 16-20 dB gain so all combined should give over 30 dB of isolation for not a lot of money.

Mike

edit - I guess if you only want to go to 13cms https://www.amazon.co.uk/Satellites-Sat ... B077DP3T28 is an 8 way splitter for £7 covering 5MHz to 2.7 GHz. You have to deal with F-connectors though. Maybe separate out 9cm and 6cm on a separate path (diplexer/relay).

DL5BCA
Posts: 64
Joined: Tue Jun 30, 2020 11:59 am

Re: Coax Switch for different Bands

Post by DL5BCA » Thu Jul 02, 2020 7:03 pm

Hey guys,

Thank you all for the answers.

73 Thomas DL5BCA
73 Thomas
DL5BCA

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