Brian, the little SMA relays do vary, the ones we pick up may well have done 10,000 operations before we get them so unless they are brand new its a good idea to measure them, a first check is just the contact resistance, if its not 0.1R there’s a problem. Despite their appearance they are NOT waterproof, very often the case is just a press fit but water can also penetrate down the connector threads....I have experience here! HOWEVER they are often recoverable. you can quite often unscrew the connectors by the clever use of an old SMA connector shell and a locknut and then you can clean up the thread, which my have ally oxide on it, and polish/clean the gold plated contacts. But a first check for me is just to measure sun noise without the relay or to use my PANFI to measure NF with / without the relay. 9 times out of 10 when I notice the moon noise is a bit low its a relay problem. The little square transfer relays( 4 connectors) that I use at 9cm and above I have found to vary a lot in both loss and especially in VSWR and for those freqs you need to actually choose one using something that will measure 0.1dB and >20dB RL. I looked into the connector loss issue some years ago now and concluded ( from manufacturers data) that you probably need to assume 0.05dB per connector pair so I always build my preamps so they can connect directly onto the relay, in most cases this means a custom bush and a short, 15mm or so length of 141 with a male connector on it. Stainless steel connectors are best avoided but just as important is to make sure the teflon faces are clean and to clean the threads. However I stll cant reconcile the level of loss associated with a SS connector with you only being able to hear Dom!! 73 Peter G3LTF From: Brian, WA1ZMS Sent: Wednesday, December 05, 2012 2:55 AM To: moon-net(a)mailman.pe1itr.com Subject: [Moon-Net] Dangerous NF questions...(long post) Gentlemen- I know the topic of NF has been a very debated one of late. But being a Sr. RF Engineer for 30+yrs in my day job and ham even longer……..I am looking for factual and measured data on a very specific topic that can impact NF measurements and ultimate RX performance. The motive for my investigation is a result of my continuous battle with poor EME RX performance on my small dish (3.2m) EME system. I have much more TX power than most for a small dish operation and noticed that my RX was acting worse over time despite my improvements to my dish feed and what I hoped would result in a better G/T value. The short answer is that after only one CW QSO this weekend with HB9BBD (Thanks for a new QSO!) I stopped operating since it was clear that my RX was worse now than ever. The root cause was an SMA LNA protection relay that now has much more insertion loss than it ever did. (was 0.1dB measured when I built the system and is now 0.3dB) All that is background info. My question now is: Other than RW3BP’s excellent report on optimizing the G4DDK LNA23 for an even better NF, who in the EME community has tried to quantify the effects of the often-used relays AND more importantly the connectors and adapters that we often find in our LNA systems? My focus is on the fact that most of the SMA connectors that are made today have only a very thin layer of gold plating on top of a nickel plate which is on the base metal which is brass. In my day job while using my shack as my lab, I have been able to build a VHF PIM measuring system that can measure a 3 to 5dB difference in PIM between a single silver-plated body type-N connector has a gold plated (with nickel under plate) center pin vs. a pure silver plated center pin. (This is in the region of -140 to -150dBc.) I know there are many opinions, but does anyone have any measured data they can share? Even a single data point can help guide me. I know I am entering into the area of true metrology where I want to determine if a 3.5mm connector with a stainless steel body is as good as an SMA that is either silver plated or has gold-direct-on brass plating. I have yet to find a source of silver-on-brass plated SMA connectors like RW3BP used, but if anybody knows of a source please let me know. My apologies for the long e-mail, but I wanted to communicate the details. 73, -Brian, WA1ZMS/4 -------------------------------------------------------------------------------- _______________________________________________ Moon-Net posting and subscription instructions are at http://www.nlsa.com/nets/moon-net-help.html

Hello Brian, As it happens I am currently doing the kind of measurements you ask for. I have been using 144 MHz for proof of concept and I can clearly see the differences in losses due to different dielectric materials in adaptors. I can however not see the losses in a chain of 10 series connected SMA cable connectors on short pieces of RG400 cable. Each cable is only 47 mm from connector ent to connector end so the 10 pairs of SMA connectors with cables in between is only 0.47 m. The losses do not difer significantly from the losses of 0.47 m RG 400 cabale with just one connector in each end. I had thought that 144 MHz would penetrate gold better than 432 and see more of the nickel, but maybe the nickel layer is too thin so 144 MHz goes mainly in the brass beneth?? By use of circulators we can measure NF differences very accurately: http://www.sm5bsz.com/lir/nfprec/hb9dri-nov12.htm It is possible to separate real losses that cause NF degradation from mismatch losses that are harmless. In your case I strongly suggest you have a problem with contact resistance in the relay. I have seen that once. It was a relay used to switch between polarizations. The observation was that the Rx was dead after switching from H to V. Just transmitting a single Morse dit would restore full Rx sensitivity. When opening the relay I could see a very small black point on the contact surface. After some polishing the relay was ok and served me well until a storm took down my antenna many years later. The problem did not affect my ordinary receive channel for which each polarization had its own preamp, it only affected the signal to the PIN diode switch which I used for receive when relays for preamps were in the tx position. If you measure the relay at very low power and look for the attenuation and input impedance you may see that the contact resistance changes from time to time when you switch the relay on and off. I will undertake a study of losses in connectors and adaptors on higher bands. There is an alternative to sending high power through and look for ther heat:-) Losses are typically much smaller than 0.1 dB which includes mismatch losses. (But there are adaptors with poor dielectrics that give significant losses. I have such for UHF and BNC. I have not found anything bad for N or SMA yet.) 73 Leif / SM5BSZ