Re: SSB Masthead preamp

Alan G0XBV

Before you go laying out dosh on this project, Mike, you might want to check this out.

From this data, it doesn't look like this a top notch switch for 23 cms.  Look at the isolation figure at 1000Mhz - that's not a whole lot!  There are others from the same stable that are better, and these will typically have shorting contacts that allow for much better at least two orders of magnitude!  These will cost proper money as new. If I recall correctly, the CX-520D is such a device.  There are even better types that are much more suited to use above 1GHz.

I'm wondering if your original thoughts re that previous project might not be too far from the truth here too.  Food for thought anyway.



-----Original Message-----
From: 'mike' mb.golfmad@... [ukmicrowaves]
To: ukmicrowaves
Sent: Wed, 5 Aug 2015 16:45
Subject: Re: [ukmicrowaves] Re: SSB Masthead preamp


Hi all,
Latest update on my SSB preamp.
On the advice of Steve M0BPQ, I contacted Henry's Radio in the US regarding parts for the CX-531 and although not being able to offer any spares for the bits I needed, they were kind enough to offer me a new relay at a very attractive price. way-hay!!  Alan Melia has also been extremely helpful, so I think I have a result on the tinplate box too..
Now if I can now get an upgrade on the actual device and get the NF below 0.5dB...
Thanks to all who offered advice and ideas.
Further to Peter GM4BYF's posting, boy am I lucky someone has his in bits too...Peter can I contact you off reflector? I have some odd work on the link between the 2 relays.. it might be a bit of DIY...would be nice to compare..
Mike G6TRM


----- Original Message -----
Sent: Wednesday, August 05, 2015 3:28 PM
Subject: Re: [ukmicrowaves] Re: SSB Masthead preamp

Hi Mike
As it happens I have my SSB preamp apart. Looking at it I conjecture – and it is only conjecture – that you could be able to access the the coaxial relays.  You would have to undo the securing screws on the two N types and PL259 sockets on the front panel with the flange.  It looks like if you then undo the securing screws on the underside of the PC board which hold the relays down, and carefully desolder the two centre pins and the supply wires to the coils, the relay system will lift out. Then there is an access panel on the side of each relay ( can’t quite see the type of screws ) which may allow you to desolder the centre pin of the faulty N-type and replace it. As I say this is all conjecture on my part. It would then be worth improving the first semiconductor – Dubus had an article a couple of years ago which detailed how to do this. By the way I have a schematic for the SSB23MkII if you should need it.
Good Luck
Sent: Wednesday, August 5, 2015 3:01 PM
Subject: Re: [ukmicrowaves] Re: SSB Masthead preamp

Hi Phil, thanks for the suggestion, the plug still works and makes contact...I just don't know how well !  I had thought of a more permanent solution along similar lines.
I now have another fly in the ointment as it were, my DB6NT transverter has a better NF than the preamp and as I only use it for roving and only use a small length of coax (LDF2-50) I'm not sure if there is much point...Still, if I can overcome the N type problem, then maybe a better device would be possible...Trouble is I've done similar before, started with something second hand, thought I would do it up, at the end of it all, I realise I have spent more that a new one would have cost, taken hours of my time to sort and it still looks what it is second hand !!
I never learn!!
Mike G6TRM
----- Original Message -----
Sent: Wednesday, August 05, 2015 2:32 PM
Subject: [ukmicrowaves] Re: SSB Masthead preamp
If you cant replace the n-type you might be able to solder a short length of coax to an in-line N-type socket to the remains of the existing one just to prove if it works. 

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