Bob VK2ZRE has forwarded the following info regarding a Passive Intermodulation (PIM) distortion – Bob adds:

This article may (should) be of interest to our members.  This is yet another mention and “explanation” of the “rusty bolt” effect.

In short, thanks to Keysight Technologies (emphasis mine) – Passive intermodulation (PIM) is a form of intermodulation distortion that occurs in passive components such as antennas, cables, connectors, or duplexers with two or more high-power input signals.  PIM in the transmission path degrades quality of the wireless communication system.

PIM is becoming a critical parameter recently due to installation of new technologies in wireless communication industries such as higher RF transmission power, multiband operation with a shared common antenna, or wider bandwidth signals with higher probability of PIM in the receiver band.

The article Bob has supplied is from Pasternack Enterprises who provide Low PIM cable assemblies, connectors, adapters, antennas and tappers designed to address applications where PIM can be an issue.  Note that this info is aimed at RF Engineers who work with LTE networks.

Pasternack writes:

What is PIM?

PIM, or Passive Intermodulation, is a type of signal distortion that has become increasingly important to detect and mitigate since LTE networks are particularly sensitive to it.

PIM is created when there are two or more carrier frequencies exposed to non-linear mixing.  The resulting signal will contain additional, unwanted frequencies or intermodulation products.  As the “Passive” portion of the name implies, this non-linear mixing does not involve active devices and is frequently caused by the metallic materials and workmanship of the interconnects and other passive components in the system.  Examples of causes of non-linear mixing:

• Imperfect electrical connections: surfaces are never perfectly smooth so the areas of contact can have high current densities which can cause heating through a restricted conduction path causing a resistance change.  For this reason connectors should always be tightened to the correct torque.
• Most metal surfaces have at least a thin layer of oxide which can cause tunnelling, or simply cause a reduced area of conduction. Some believe that this produces the Shottky effect.  This is why a rusty bolt or metal roof near a cell tower can produce a strong PIM distortion signal.
• Ferromagnetic material: materials such as iron can generate large PIM distortion and should not be used in cellular systems.

As wireless networks become more complex with multiple technologies and system generations in use at a single site, the signals combine to generate this undesired distortion, which interferes with the LTE signals.  Antennas, diplexers, cables, and dirty or loose connectors can be sources of PIM, as well as damaged RF equipment or metal objects near or at a distance from the cell site.

PIM interference can have substantial impacts on the performance of LTE networks, which is why it is so important to wireless operators and their contractors to be able to test for, locate and mitigate PIM.  Acceptable PIM levels vary by system but as an example Test Company Anritsu said that drive tests have found an 18% drop in download speeds when PIM levels were increased from -125 dBm to -105 dBm, even though the latter number can be considered an acceptable PIM level.

Where is PIM tested?

Individual components are often tested for PIM both in the design and production processes in order to ensure that they are not significant PIM sources once they are installed – however, installation is still a critical piece of PIM mitigation because proper connections are critical.  In the case of distributed antenna systems, in some instances the system is tested for PIM as well as individual components.  PIM-certified equipment is becoming more common.  Antennas, for example, may be PIM-certified to a level of -150 dBc and those requirements are increasingly strict.

PIM is also assessed during the siting process for cellular sites, ideally before the cell site and antennas are placed as well as during the installation process.

Not Ham related, but here’s an excellent set of articles on Forgotten Audio Formats from (the always fantastic) arstechnica.com.  How many did you own?  How many did you have to repair?

Wire Recording

8 Track Tape

Elcaset

Digital Compact Cassette

The Highway Hi-fi

Talking Rubber (!)

The following is an excerpt from the International Amateur Radio Union Monitoring System (IARUMS) Region 1 December 2016 newsletter which can be read in full here.  The IARUMS monitors the state of the Amateur bands and reports on interference and Intruders.  See their website here.

VK5EEE offers the following opinion piece on the state of the Australian Amateur scene:

[Commenting on previous reports of South American Fisherman using the Ham bands]

I’m not surprised to hear this about Latin American region.  My antennas seem to favour that area but I almost never (at least on CW) hear any active radio hams there.  I think it could be useful to report findings from around the world about the general state of QRM on our bands, and what could be done short, medium, long term to forecast and reverse these trends.  In our area our 40m CW band is useless in the evenings due to strong SSB QRM every 5kHz USB and LSB — which thus covers the entire CW band — from powerful Indonesian pirates.  These pirates also seem to occupy a great many frequencies between 10000 and 11400kHz – there are huge number of them in a population of 200 million.

THAILAND A GOOD EXAMPLE

But we can contrast Indonesia to Thailand where there are a total of ZERO pirates on HF.  In HS-land you cannot buy any gear without showing license.  You cannot import either without inspection.  And you cannot operate in any location without a location license in addition to your operating license, and this system clearly works, no matter it is a bit slow to get a ham license.

This even though the HF population of HS amateurs is quite small, perhaps 200 or less, while the VHF population of HS amateurs is high, a quarter million or so.  The radio amateur license density per population in Thailand is at a rough guess 10 times what it is in Australia.

CW BAND PRIME TARGET FOR PIRATES

For CW operators, the problem is pirates which almost invariably use SSB, of course use the CW band, because there, they hear no other SSB. They don’t use the SSB parts of the band because then they would be afraid when they hear a strong local SSB radio amateur telling them off, or even direction finding them potentially.  So some CW operators, myself included, have gravitated to the SSB part of the band, which after all is shared CW-SSB it’s fine for CW, and due to radio amateur inactivity, it is also often empty.  Right now, 20m and 17m are open — and yet tuning the entire bands from top to bottom and bottom to top several times, I did not hear ONE radio amateur signal on CW nor SSB, nor Data.

NATIONAL SOCIETY FAILURE

During the week day, and remember a great many hams are retired, I can more often than not tune the entire 40m band also without hearing any SSB, Data, nor CW.  And this even though the now manifestly corrupt national society seeks in a misguided effort to make amateur radio a public CB social media extension, they have not succeeded.  They have taken the view that amateur radio is in decline and the way to reverse that is to make it easier to get a license at least at lowest level (which still gives 100W, though officially 10W, to anyone sitting a short course without possibility of failure, and then access to 80m, 40m, 15m, 10m) and yet the vast majority of these don’t get on air since amateur radio offers little to them compared to internet social media. Continue reading →

Quite a few members (myself included) have been tempted by the new QYT KT-8900D.  $109AUD (shipped) buys you a Dual Band Quad-Standby Colour Screen Mini-Mobile rig that puts out a healthy 25W in a tiny package, complete with little cooling fan, a great little speaker and (from all the ones we’ve used) good quality transmit audio.  I was fortunate enough to get mine with a $20 discount coupon (thanks eBay!) that made it a $90 purchase.  How can you say no?

Side note: Yes, these model numbers are getting ridiculous.  How many 8900 radios can there be?  As many as there are 9800s?  What about the 7800s?  Argh!

Lyle VK2SMI spotted an interesting accessory specifically for this radio today – a Bluetooth Radio Speaker Mic!  Integrated Bluetooth options in higher-end radios like the Icom ID-5100A and the Yaesu FTM-400 aren’t uncommon these days – but if you opt for those (stupidly) expensive options you get yourself a Bluetooth headset – not something in the form factor of a traditional radio mic.  $59.99AUD (shipped) is the right price too!  Check out the BT-89:

Included is a 1400mAh battery in the mic giving a quoted 2 days usage (with 1 week standby).  Usable range is quoted to be 10 meters from the supplied dongle, and the dongle gets its power from the radio itself.  As pictured, the unit is supplied with a USB plug pack and a USB to 3.5mm cable for charging the mic.  No more mic cables in the car (or less cables across the bench) sounds enticing doesn’t it?  I’m not sure how good the radio will look with that short dongle cable leaving the dongle dangling 2cm in front of the mic port though…

Compatible radios are listed as the QYT KT-7900D, KT-8900, KT-8900R and KT-8900D (see aforementioned comment about model numbers).

Conversation turned to how easy it may be to adapt this unit to other radios – different mic pinouts would be one hurdle to overcome (which should be relatively easy with a small home-made adaptor), supply voltage from the radio to the dongle may be different (less easy to overcome, but doable) and finally the impedance/output that the Bluetooth receiving dongle presents to the radio’s mic input may also be an issue.

Food for thought.

Now if someone could get to making an adaptor that lets you use your in-car (factory) Phone Bluetooth connection with (any) mobile rig (along with a nice cordless PTT), I’d be eternally grateful!