LINK Updates June 2012
Meter Sales page is now: http://www.Navigator-Interface.com/naviusa_010.htm
eHam reviews of the meter: http://www.eham.net/reviews/detail/4210
REPOST & UPDATE: Had a very nice QSO with Clint KK7UQ by PSK31 using the Flex-5000A and after discussion decided to repost an update on his excellent PSK31 IMD Meter. I originally built a kit version, but presently only a fully built version is offered.
This has to be one the most fun kits to build where the finished product is something you just can’t buy easily – the KK7UQ IMD PSK meter.
Clint KK7UQ is a wonderful person to deal with, and I’ve had the pleasure to work him as well. His meter concept is simple:
The RF signal is picked up by a short whip antenna on the meter, fed into an AGC controlled RF amplifier, the signal is detected, sampled with an A/D converter under the control of a micro controller. The signal is analyzed by firmware on the micro controller and the equivalent IMD is calculated and displayed on a 3 digit LED array built into the IMD Meter. (from Clint KK7UQ’s website)
Since not all of us are up on the jargon, let’s run it down.
PSK – Phase Shift Keying – One of the Most Popular Digital Modes (usually PSK31 or PSK63 – the numbers indicate speed) – Full write up at: http://en.wikipedia.org/wiki/Phase-shift_keying
IMD – Intermodulation distortion – The “noise” sub-optimally tuned up PSK transmissions are prone to. – Again a fuller nice write up is at the Wiki: http://en.wikipedia.org/wiki/Intermodulation_distortion
A/D – Analog to Digital converter – basically this circuit digitizes for processing an analogue signal – see: http://en.wikipedia.org/wiki/A/D
AGC controlled RF amp – A radio Frequency Amplifier with Automatic Gain Control
The IMD Meter Building Experience is one of great fun and an outstanding product when you’ve finished.
The Kit version had been available directly from Clint KK7UQ or the recently added Fully Assembled version from RigExpert [edited 02 DEC 2008]
UPDATE From Clint Hurd KK7UQ – 02 DEC 2008:
Hi Steve – I enjoyed our QSO yesterday on 20m PSK. You asked for comments on the IMD Meter page. I have 2 comments: 1) The reference to “RigExpert” with accompanying URL is no longer valid. It should be changed to: “USInterface” with the URL of
http://www.USInterface.comSEE ABOVE June 2012 Updates 2) The IMD Meter is only available in fully assembled form from US Interface. I no longer provide kits. Thanks for the nice writeup. Clint KK7UQ
Steve – some additional thoughts:
When the IMD meter was designed, the FS (field strength) was added as an afterthought. The number output is related to the attenuation of the AGC circuit – it turns out to be about 1 dB per digit. I have found, and others have told me that the FS is useful. In my case, my antenna is an 80 meter full wave horizontal loop, located several hundred feet from the shack. I have a remote tuner there to minize transmission line loss when the frequency is away from the resonant points. I use the FS mode to let me know if the tuner is working and that RF is actually getting out. Of course, the FS varies from band to band, since the pattern of the antenna changes with different bands, but the FS per band is very repeatable. I have already detected a bad connection at the feed point, and a tuner that didn’t like running in contest mode for 6 hours straight.
Another case was a Russian ham who used his IMD Meter in FS mode to help tune his mobile screwdriver antenna.
So this has turned out to be more useful than first thought.
The IMD Meter is manufactured in the US. N3JJA manufactures the IMD meter; sales and service is by Glenn W3GWW. The parts, of course come from all over the world, but the PCB, the cases and the assembly are all done in this country.
Glenn W3GWW also sells the Navigator interface which is one of my designs. It is also manufactured in the US. Assembly is done by automatic equipment in California, testing is done in Washington, and sales and service are done in Maryland. The unit has undergon Part 15 FCC certification and is designed and manufactured to ROHS standards.
73, Clint KK7UQ
Also a nice checklist for a PSK station setup can be found at:http://www.psb-info.net/Station-Setup-Checklist.html
Either KK7UQ’s IMD Meter has my Recommendation, and are a welcome addition to any shack with digital operations.