Perils of Patch Leads

Discussion about this major DATV Project. See also https://wiki.batc.tv/The_Portsdown_Transmitter
M0YDH
Posts: 67
Joined: Sat Dec 31, 2016 5:59 pm
Location: Wolverhampton IO82WO

Perils of Patch Leads

Postby M0YDH » Fri Nov 24, 2017 1:47 pm

Here's a lesson that I've learnt the hard way.
I tweeted https://twitter.com/DavidHo34732663/status/927586601202585600 at the beginning of November

My Portsdown was working on my 50th birthday fine. A few days later I uploaded the week's sensational software updates and checked that it was running again using the same M0HMO power meter. Nowt came out . Oh dear. There's a lot hanging on this device working. Dave G8GKQ wrote me a note asking what was the matter and took me through a series of tests. What a very decent man. These concluded with "send the oscillator board to me for testing on a known good set up". Meantime I took some filters to our club in Wolverhampton for spectrum analysis and alignment. SMA patch leads were borrowed from my kit and nothing worked. Ron M0RNW scratched his head a great deal and suddenly announced "there's an open circuit and I think it's your patch leads". Sure enough Reverse SMA patch leads had wriggled into my kit. (The leads that we did use afterwards came from Dr Frankenstein's lab! Nice W1GHZ comb line BPF for 437MHz but I think the 6dB insertion loss would go on a modern instrument with normalised leads) . I don't remember ordering reverse SMA leads so I must have picked them up from a for sale table at Telford or Finningley. I thought about all the tests that had gone poorly of late and concluded reverse SMA test leads had done for my Portsdown power measurement. I wrote to Dave, apologised and owned up to incompetence. Curiously enough there was nothing wrong with the oscillator board. The Portsdown is back together and working fine.

So if like me you've never seen reverse SMA connections, complete with a receptacle hole where a pin ought to be, take care when you suddenly have a duff bit of kit which worked a few days before. Have a look what's inside one of the gold mounting nuts and beware of the Perils of Patch Leads. :?

73
David M0YDH

G3JZF
Posts: 10
Joined: Tue Jul 11, 2017 6:43 pm

Re: Perils of Patch Leads

Postby G3JZF » Sat Nov 25, 2017 11:58 am

David

I too got caught out on this one but having previously sorted out my WIFI router I had come across RP SMA leads before and I soon traced my Portsdown LO problem to one of these blighters! It did not stop me picking up 5 leads at Newark and only realising my mistake when I got them home. :(
If these things happen on 50th birthdays, I will have to take care on my 50th wedding anniversary next year!!.
I note that you have access to a spectrum analyser at the Wolverhampton club and I would be very pleased if next time you do this, I could come over and bring my Portsdown and amplifier.
I am now ready to test my Portsdown barefoot and when you are ready, please let me know. I have beams up for 70cm and 23cm and a collinear on 2m/70cm for talk back.

73
John, Sutton Coldfield

g3zgz
Posts: 24
Joined: Thu Jul 16, 2015 1:36 pm

Re: Perils of Patch Leads

Postby g3zgz » Sat Nov 25, 2017 12:38 pm

An even beter one to watch out for is with low cost sma ready made leads.

Some suppliers fit SMA reverse connectors to their leads and make them into "normal" male SMA's by adding a centre pin that just pushes into the female centre of the reverse SMA's.

They can then sell them as normal or reverse by adding or removing the centre adaptor pin.

Yep, you guessed it, that I had a lead like that where the centre pin fell out and turned my SMA lead into a reverse SMA lead on one end!

As you have found out, it works as a great, but unmatched attenuator!

Even worse on 10GHz as the "loss" is far less than 23cm and it's not easy to spot, ESPECIALLY on your 50th of anything.
I know!

73

Dave

G3ZGZ

g3zgz
Posts: 24
Joined: Thu Jul 16, 2015 1:36 pm

Re: Perils of Patch Leads

Postby g3zgz » Sat Nov 25, 2017 12:39 pm

Bye the way, I notice there are a lot of Portsdown owners called Dave / David.

Is this a requirement, I wonder.

Dave.
G3ZGZ

M0YDH
Posts: 67
Joined: Sat Dec 31, 2016 5:59 pm
Location: Wolverhampton IO82WO

Re: Perils of Patch Leads

Postby M0YDH » Sat Nov 25, 2017 12:53 pm

Thanks for the sympathy chaps.
In any walk of technical life nothing functions without numerous Daves and Davids . Our engineering office and any railway preservation group that I join are a case in point. Over to the west it's the same for Dafydd, Dewi, Dai in the south and Dei in the north. I'm Dei when I'm speaking in Welsh.
Hwyl fawr
Dei M0YDH

M5TXJ
Posts: 44
Joined: Wed Jul 05, 2017 8:34 pm

Re: Perils of Patch Leads

Postby M5TXJ » Sat Nov 25, 2017 3:31 pm

Dave/David's are an essential in any arena LOL

In 1986 I was on a Royal Observer Training Camp at Newcastle where we were billeted in the University halls of residence. On the floor of 8 rooms where I was, there were 7 Davids. Of course some comedian re-labelled the button in the lift, "Camp David".

73 Dave


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