Engineering Radio – Page 35 – One Hundred percent Human Generated Content for your Reading Enjoyment

Speaking of Radio…

I was talking to a friend from Russia about history, my job, and various other things that are going on in my life. I received this reply, which I thought was interesting on a number of levels:

I’m glad we are on the same page about the era of the ‘cold war’. We were interested in your life even more than you in ours. We had almost no sources of information except for ‘The morning star’ which is a newspaper of the Communist party of Great Britain. The Voice of America and the Liberty (or Freedom, I have no clue because for us it was ‘RADIO SVOBODA’) were extremely hard to tune on. All foreign broadcasts were jammed. So to listen to the station you should maximize the volume up to the limit which was dangerous. Soviet houses are not at all soundproof and your neighbors could easily rat on you. Since that time I’d been dreaming of a small radio with could receive a clear signal from abroad. Of course we have the Internet broadcasting now but they often use old recording instead of live air and the signal depends on your data carrier. You should be online, you should have an app and unlimited data on your contract, your phone should be charged all the time. Too many conditions. Unfortunately a lot of foreign sites are banned here and the trend is to make this number bigger and bigger.

I find that perspective interesting. We take for granted our ability to listen to information and listen to different points of view, even those we don’t agree with. There are still trouble spots in the world and some people are not as fortunate. It is very easy to block internet traffic and there are several countries that currently block access to some or all of the internet, for the safety of their citizens, no doubt. Ideas are dangerous.

VOA/RFE transmitter site, Biblis Germany. Photographer: Armin Kübelbeck, CC-BY-SA, Wikimedia Commons

In the last ten to fifteen years, many large government shortwave broadcasters have reduced or eliminated their programming favoring an internet distribution model. This is a mistake. It is very difficult to successfully jam terrestrial radio broadcasts. Shortwave Facilities are expensive to develop and maintain, there is no doubt about that. However, as the Chief Engineer from Radio Australia (ABC) once told me “HF will get through when nothing else will.” Ironically, ABC has eliminated its HF service on January 31, 2017.

It seems to me that a sort of “Shortwave Lite” version of broadcasting might be the answer. Use more efficient transmitters with lower power levels closer in to the target areas. Such transmitters could be coupled to rotatable log periodic antennas to target several listening areas with one system, thus greatly reducing the number of towers and land required. Solid-state transmitters with a power of 10-50 KW are much, much more efficient than their tube-type brethren.

DRM30 (Digital Radio Mondiale) has not gained widespread use in the MF and HF bands. Like its HD Radio counterpart, the lack of receivers seems to be one of the adoption issues. As of 2017, there are only four DRM30-capable receivers for sale not counting software plug-ins for various SDRs. That is a shame because my experience with DRM30 reception has been pretty good. I have used a WinRadio G303i with DRM plug-in, which set me back $40.00 for the license key (hint for those nice folks at the DRM consortium; licensing fees tend to quash widespread interest and adoption).

CFRX, Toronto coverage map, average HF propagation conditions

Finally, I have advocated before and still advocate for some type of domestic shortwave service. Right now, I am listening to CFRX Toronto on 6070 KHz. That station has a transmitter power output of 1 KW into a 117-degree tower (approximately 50 feet tall) using a modified Armstrong X1000B AM transmitter netting a 15-32 µV received signal strength some 300 miles away. That is a listenable signal, especially if there is no other source of information available. The average approximate coverage area for that station is 280,000 square miles (725,000 square kilometers). That is a fairly low overhead operation for a fairly large coverage area. Perhaps existing licensed shortwave broadcasters should be allowed to operate such facilities in domestic service.

The point is before we pull the plug on the last shortwave transmitter, we should carefully consider what we are giving up.

Part 101, Private Fixed Microwave Service

I have been tasked with installing one of these systems for a sixteen-channel bi-directional STL. This system was first mentioned here: The 16 channel bi-directional STL system. As some of you pointed out, the unlicensed 5.8 GHz IP WLAN extension was the weak link in this system. It was not an interference issue, however, which was creating the problems. The problem was with layer two transparency in the TCP/IP stack. Something about those Cambium PTP-250s that the Wheatstone Blade hardware did not like and that created all sorts of noise issues in the audio. We installed the Wheatstone Edge Routers, which took care of the noise issue at the cost of latency. It was decided to go ahead and install a licensed link instead of the license-free stuff as a permanent solution.

Thus, a Cambium PTP-820S point-to-point microwave system was purchased and licensed. The coordination and licensing took about three months to complete. We also had to make several changes to our network architecture to accommodate the new system. The PTP-820 series has a mast-mounted radio head, which is the same as the PTP-250 gear. However, for the new system, we used three different ports on the radio to interface with our other equipment instead of the single port PTP-250 system. The first is the power port, which takes 48 VDC via a separate power cable instead of POE. Then there is the traffic port, which uses Multi-Mode fiber. Finally, there is the management port, which is 1GB Ethernet and the only way to get into the web interface. The traffic port creates a completely transparent Ethernet bridge, thus eliminating all of the layer two problems previously encountered. We needed to install fiber transceivers in the Cisco 2900 series switches and get those turned up by the IT wizards in the corporate IT department.

Andrew VLHP-2-11W 11 GHz microwave antenna — Andrew VHLP-2-11W 11 GHz microwave antenna

The radios mount directly to the back of the 24-inch 11 GHz Andrew antenna (VHLP2-11) with a UBR100 interface. The waveguide from the radios is a little bit deceptive looking, but I tried not to overthink this too much. I was careful to use the O ring grease and conductive paste exactly where and when specified. In the end, it all seemed to be right.

Cambium PTP-820S mounted on antenna — Cambium PTP-820S mounted on Andrew antenna

Not wanting to waste time and money, I decided to do a back-to-back test in the conference room to make sure everything worked right and I had adequately familiarized myself with the ins and outs of the web interface on the Cambium PTP-820 radios. Once that was done, it was time to call the tower company.

One side of these is mounted on the studio building roof, which is a leased space. I posted RF warning signs around the antennas because the system ERP is 57.7 dBm, which translates to 590 watts at 11 GHz. I don’t want to fry anybody’s insides, that would be bad. The rooftop installation involved pulling the MM fiber and power cable through a 1 1/4-inch EMT conduit to the roof. Some running back and forth, but not terrible work. I used the existing Ethernet cable for the management port. This will be left disconnected from the switch most of the time.

Cambium PTP-280S 11 GHz licensed microwave mounted on a skirted AM tower

The other side is mounted at about 85 feet AGL on a hot AM tower. I like the use of fiber here, even though the tower is skirted, the AM station runs 5,000 watts during the daytime. We made sure the power cables and Ethernet cables had lighting protectors at the top of the run near the dish and at the bottom of the tower as well as in the transmitter room rack. I know this tower gets struck by lightning often as it is the highest point around for miles.

PTP-820S RSL during aiming process — PTP-820S RSL during the aiming process

Aligning the two dishes was a degree of difficulty greater than the 5.8 GHz units. The path tolerances are very tight, so the dishes on each end needed to be adjusted in small increments until the best signal level was achieved. The tower crew was experienced with this and they started by panning the dish to the side until the first side lobe was found. This ensured that the dish was on the main lobe and we were not chasing our tails. In the end, we achieved a -38 dBm RSL, the path predicted RSL was -36 dBm so close enough. This means the system has a 25 dB fade margin, which should be more than adequate. While were aligning the transmitter site dish, a brief snow squall blew through causing a whiteout and the signal to drop by about 2 dB. It was kind of cool seeing this happen in real-time, however, strangely enough, the tower crew was not impressed by this at all. Odd fellows, those are.

Currently brushing up on FCC part 101 rules, part C and H. It is always good to know the regulatory requirements of any system I am responsible for. As AOIP equipment becomes more mainstream, I see many of these types of installations happening for various clients.

The Gates Air FAX-10, Numero Dos

This is the second Gates Air FAX-10 that I have installed. This one is in the shipping container transmitter site from the previous post of the same name. In this case, we dispensed with the equipment rack that came with the transmitter and installed it in a standard Middle Atlantic rack. The Harris rack configuration wastes a lot of space and since space is at a premium, we decided to do it our own way.

Gates Air FAX-10 in Middle Atlantic rack

The bottom of the rack has the transmission line dehydrator. The top of the rack has the Dielectric A60000 series 1 5/8 inch coax switch, a Tunwall TRC-1 switch controller, and the Burk ARC-16 remote control. I cut the rack panel top to accommodate the coax switch. The racks were removed from an old studio site several years ago and have been in storage since then.

The Gates Air FAX-10 transmitter on the air, running a sports-talk format.

Dummy load and Broadcast Electronics FM10B transmitter

View from the other side showing the test load and BE FM10-B transmitter. This transmitter had a problem that I have run into before with BE FM transmitters. The jumper between the exciter and IPA had the wrong phase rotation causing reflected power. I added a foot to its length and that problem disappeared.

Hoth

Alternate title: Winter in the Northeast

For all you southerners and west coast people, we have been having an average winter here in the Northeast. While many of our transmitter sites are drive-ups, we have several located at ski area mountain peaks. Technically, those mountain-top transmitter sites are a fantastic way to get the Height Above Average Terrain (HAAT) way up there. Logistically, they are much more difficult to deal with. Installing a new transmitter or even refueling a generator takes major effort. Working in the cold and wind is much more fatiguing and requires paying special attention to protective clothing, hydration, exposure, etc.

Here are a few pictures from Killington and Pico mountain ski areas in Vermont

The snow grooming machine is the only way to bring anything up to the top of the mountain during the wintertime. In this case, I needed to replace a BW Broadcast TX 1500-watt transmitter.

Even with the snow grooming machine, the last few hundred yards need to be walked. Fortunately, the snow is packed and not too deep here.

Tower is encrusted with ice. I can tell the tower climber is having a great day:

Tower climber working on ice encrusted towe — Tower climber working on ice-encrusted tower

Riding the chair lift back down the mountain gets plenty of strange looks from those skiers coming up:

Over on Killington Peak, conditions are actually worse.

The ERI antenna heaters cannot keep up with the ice buildup.

ERI two bay antenna with ice. — ERI two-bay antenna with ice.

The general manager insists that this winter is not too bad and everything should be working right. My statement to her: Based on my 27 years of experience, your shit is fucked up. But if you know how to fix this, come on up and show me. She deferred.

What the fire tower looked like last winter.