The KEØVH Hamshack For August 2014
By Jack Roland, CBRE, AMD and CBNT
KLove /Air 1 EMF Colorado Engineering.
As you may have heard I have been doing a lot and experimenting with the little SDR USB Dongle that I ordered from Amazon.com. I am also in the process of setting up a good monitor antenna at home to hook into the SDR for monitoring signals that I can receive at my home in the Hamshack. The dongle and FREE SDR Sharp (one among many) are really easy to setup in Windows and use the features that the system offers.
The $8 USB Dongle from Amazon.com
The Spectrum analyzer window will show about a max of 3 mHz bandwith, and also has IF, MPX, & Audio Spectrum plus a waterfall display. The size of the dongle is only slightly bigger than a standard USB thumbdrive, so is very easy to carry along with your laptop. The software even can decode RDS as seen in the pictures below. In these pics I was looking at KLDV, 91.1 Denver from the Hamshack on a VHF mobile antenna.
There is also the feature of being able to use the system for a “virtual aircraft radar’ setp allowing you to track aircraft within a radius of your receive site and plot their positions on a real time display. The January 2013 edition of QST has an article detailing how to do that. I will also be reporting on that here soon as I intend to try it.
See that article here at: http://www.arrl.org/files/file/QST/This%20Month%20in%20QST/January%202014/VirtualRadarJan2013QST.pdf
The Dongle comes with a small mag mount antenna with a MCX connector. Some dongles come with different connections so whichever one you order make sure you know what it uses. I also ordered the MCX male to SO239 female adapter, also available on Amazon so I could adapt it easily enough into my ham shack antennas. Now, you can also order the “ham it up” converter so that the software can show you amateur radio frequencies on a spectrum. Check that out also on Amazon. I just ordered one soon myself so I will write up a feature on it soon. There are of course a ton of video’s on YouTube about the SDR’s and converters and using these.
For several months now I have been battling a VERY intermittent problem at my new AIR1 station near Fort Collins and serving Denver north to Wyoming. The Armstrong FM10000-T transmitter used for the 103.9 signal had prior to us obtaining the station had had little to no maintenance or anyone really looking after it due to ownership out of state and no local engineer keeping tabs on it. The transmitter would occasionally, and sometimes much more than others simply drop RF power and then bring itself back up. And of course hardly ever when I would be in front of it. There were no alarms indications of any sort and our remote control system couldn’t catch it due to the very quick nature of the anomaly. Myself and my contractor, Greg, WB7AHO went thru the thing several times with a fine toothed comb looking for issues. We found many actually, including a tube that needed to be replaced, very dry brittle air hoses the transmitter uses to keep the PA cavity at the right blower pressure, burnt “stuff” down in the bottom of the PA Tube socket, loose rectifier stacks, bad interlock switches, and many more. After replacing the tube earlier this year and cleaning the socket well, I thought we had the problem licked as the transmitter then operated well with only very limited drops, and since we had had AC power problems on Buckhorn mountain up there, I thought, well we can operate along here until we get the “new” Harris Z12HD transmitter going, which we had obtained and physically installed, but that is another story for a later article. Then, about 3 weeks prior to this writing, the problem came back in earnest on the Armstrong. It was so bad we were getting drops 3 times a song or so. I had the NOC shut it down, let it sit for a few minutes, and turn it back on. Then it would operate a day or so before the problem resurfaced. So back up the mountain Greg and I, or Greg would go to see if we could figure it out. Now, keep in mind talking to the tech support folk at Armstrong several times too. In the past, when the previous owner would on occasion go up the site, and not being an engineer, he had tried several things including removing the reflected power cable from the output of the transmitter, just anything to keep it from shutting down, to no avail, and we had to correct all of that too.
FINALLY, about a week before this writing, Greg was at the site and he thought he would just watch the thing. He sat and stared at the metering, the IPA metering, and the exciter metering to see what might show when the transmitter hickuped! We were literally asking the Lord to let us see what might manifest itself on the front panels. Then, it happened! Greg spotted an massive modulation spike in the front panel metering of the exciter itself. Happened again a little later. Praise Jesus! Finally a real indication. Now a couple of days before too we began to hear some “popping” very lightly in the audio. That of course would indicate some possible arcing somewhere, which is where we had concentrated our troubleshooting efforts. We had measured the antenna and transmission line system with the Field Fox and visually inspected and anything else we could think of.
SO, with that information in my possession that Monday afternoon, I returned to the office/ENG shop in Denver and configured up a Crown FM-250 that was a composite audio input and can go down in wattage to the 3 to 5 watts needed to drive the Armstrong IPA. IF the IPA was having a problem too the Crown could drive the PA if need be since the IPA runs at about 200 watts. So long story winding down, the Crown SEEMS (3 days later) to be running the Armstrong stably. Now, here is the final word in the story, short of another problem .
The Armstrong driven by the Crown FM-250 The Exciter and IPA
As we were telling Armstrong tech support of our findings, they said “ oh yeah, they had seen that problem before in the FM30X-C exciter with a low pass filter in the balanced audio input stage with the XLR inputs being unterminated.” REALLY!?!?!?!?!?!?!?!?!? You couldn’t have told me that back in November when I inherited that thing?!?!?!?!?!?!?!?!?!?!?!? Evidently if you use composite audio in and not the XLR’s, there is a filter that had been problematic in the past. You know, I should have listened to my gut and replaced the Exciter with a Crown 2 months ago when I was thinking that could be the problem. Well, next time huh?
Oh and by the way, W5WCA still thinks the Armstrong would serve better in a landfill or at the bottom of the nearest cliff! I think he has a point there. And I agree with him, as of this writing (08/11) we lost the PA section and are operating on 657 watts with a backup Crown FM-600. Can’t wait to be rid of the Armstrong……
And this, from Mark, NØVUB in Omaha NE. His rebuild of his fine Hamshack!
Really nice layout Mark! Note the Heathkit SB 104 series HF rig lower left!
Don’t forget the SBE IRLP (and Echolink) Hamnet, the first and third MONDAY EVENINGS of the month. AND the EMF Hamnet now is the same manner on every Monday evening at 7pm Mountain time for radio discussions, both broadcast engineering and Amateur radio. Details on how to join are at http://www.qsl.net/ke0vh/sbehamnet. I hope you will be able to join us and share your engineering and ham exploits!
73’, God be with you, & see you next time! KEØVH