Category Archives: Science

volt/amp/watt/energy meters

Got another two of the inexpensive volt/amp/watt/energy meters from mfreelaa on eBay. These are pretty nice, especially for the $12 each including shipping.

I put two of them in series to see how well each tracked the other. There should be a very small drop in voltage for the second on in series as opposed to the first. That does appear to be the case.

The unit under test is pulling approximately 1-1/4 amps at 12 volts. Assuming these ammeters use 100 A/75 mV shunts (since the meters without built in shunts do the same and it’d be easier to keep them all the same) this would imply that the second meter should read about 0.001 volts lower than the first. However, the display precision is only 0.01 A so it’s not practical to see the difference with this small load.

After two hours now, both meters are showing 50 w-h, I’ll have to wait longer to see if they diverge from one another at all. The voltage (refreshed once per second) is generally within 0.02 volts, which is 0.15% agreement. The current reading is looser, maybe 0.2%. The power reading is quite close, but one would expect that the power reading comes from the multiplication of the v and i values. The energy reading is the time cumulative sum of all the power measurements.

Next project is to measure the efficiency of my new MPPT solar battery charger. Just need to have a sunny day!

UPDATE:

Here it is the next morning and the DUT has now pulled a total of either 261 or 262 W-h, depending on the meter read. That’s still pretty good internal consistency between meters, well under 1% difference.

So, relatively speaking, these meters are pretty consistent in their performance. Perhaps one of these days I’ll set up a calibrated load to get a better handle on the absolute accuracy. But for now, just knowing that the meters are consistent allows me to do the solar MPPT charger testing.

Update on the rooftop amp

Last time we visited the roof, the amp followed by the FM BCB notch filter was now in the die-cast enclosure, but not actually attached to anything.  Now it finally has a home, at least for now, on the tripod leg. It required a visit to Artie’s Ace Hardware in Phoenix at Tatum and Thunderbird, which until about 8 hours ago was unknown to me as a purveyor of a near infinite number of different kinds of metric fastener! Only 4 miles away, it’s a treasure to know that I can get an M4x8 mm pan head screw even late in the afternoon.

The metric hardware was required to install the steel mounting ears on the die-cast enclosure; those mounting ears accept the muffler clamps that hold the whole thing to the leg of the tripod. Later on this winter I’ll bend up some 0.032 Al sheet to act as a sun shield and remount the box on the north leg with the shield to keep it cooler during the summer. I still need to do something permanent about the power for the amp, it’s currently the solar power setup I made a couple weeks ago.

Left is input, right is output. Runs on any voltage up to about 32 vdc and down to about 7 vdc. The internal dc-dc converter keeps the amp supplied with an even 5.0 volts.

With this amp in place, my stack’o-scanners is just bangin’ along. I’ve got great reception, and no FM BCB interference. And, there’s space in the enclosure for a future Arduino or Raspberry Pi, as well as the necessary network connection.

Shocking new amplifier

Is finally built. I bought three of these a couple years ago from kuyaya520 on eBay and they’ve languished since then, heat-shrink protected and tie-wrapped in place, like for the truck’s half-deaf GRE PSR-600 scanner.

Finally put one in my new die-cast case that I got 10 of last month, and used a 82 ohm resistor to set the operating voltage to around 10 vdc when running off 13.8 vdc. According to the eBay page about the amp, its best gain and noise figure is around 9-10 vdc.

Checked out the gain, and it’s pert darn near what the vendor says it is. Don’t have a simple way to do noise figure. Need to get myself an ENR noise diode so I can do y-factor.

This amp will likely go into the truck to replace the tie-wrapped kludge… I’m starting to get reasonably good at assembling these things.

Next step on the rooftop LNA setup

This past weekend I finally started building the ultimate case to house the LNA and FM BCB filter for the rooftop multireceiver project.

Last night I did the final bit of wiring, installed a DC-DC buck converter to take +12 vdc and knock it down to 5.0 vdc.

Here’s some pics of the project.

The two separate die-cast enclosures are the LNA (lower) and the FM BCB notch filter (upper). There’s a LM2596 DC-DC converter in the lower left, and a weathertight Ethernet connection in the center-right wall. All external RF connectors are N. All internal connectors are TNC. All coax is RG316 double-shielded. I used an Ethernet connection to get power to the box and to allow the future addition of either an Arduino or an Raspberry Pi for telemetry purposes.

The overall enclosure with installed components. Got this particular enclosure for about $22 delivered – someone in Santa Maria CA didn’t want it. Was missing the base plate upon which I mounted all the components – fortunately, I had a piece of Al in the garage that was a near-perfect fit! Would have cost nearly $70 new.

The left N connector is the antenna input, the right N is the assembly output to the shack. The Ethernet connector is for future expansion and dc power.

Installed on the roof temporarily (will be mounted on the tripod to right ultimately) with power supplied by batteries in the Tupperware container.

The batteries (Eneloop AA x 10) are charged with a newly modified solar panel install. Again, over the weekend I cut some Al extrusions to replace the old way I’d attached a single 5 w solar panel, now it supports two 5 w panels for a total of 10 w. This almost guarantees sufficient charge for long winter nights.

In addition, the box mounted on the tripod already had a PoE Ethernet connection from the main rooftop unit. I use that 12.6 volt PoE  through a single 1N4001 rectifier to source power to the LNA box when the solar panels can’t provide enough charge to keep the batteries up. I want to add some telemetry (through a future Arduino or similar on the roof) to measure voltages, temperatures, etc.

 

One weird trick for making the amp behave

Alright. Things are looking much better again. Moved the LNA to its rightful position just 2 m of LMR-195 behind the antenna. Put the FM BCB band stop filter behind the LNA. Since I’m not sending dc up the coax right now, and since the BCB stop filter is in the way anyway, I bit the bullet and built myself a quick and dirty solar charging battery supply for the LNA!

5 w solar panel, purchased a decade ago from Harbor Freight; 8 NiMH AA cells in a series holder; LM2596 buck converter to reduce the battery voltage to 5.0 v; a Tupperware container to hold the batteries and converter. Impressive, no? %^) Let’s see how it survives the night.

Here’s the new block diagram – note the PCR-1000 is on one leg of the first splitter, so it should have no more than about 4 dB additional loss than when directly connected to the coax from the roof.

001 – 100 MHz, w/LNA, w/filter, w/o-3dB-splitter:

001 – 100 MHz, w/LNA, w/filter, w-3dB-splitter:

Here, the added loss from the splitter is apparent from DC to 80 MHz or so. It apparently doesn’t pass low frequencies well at all. Since the antenna is not rated that low anyway, it’s good to get rid of additional interfering signal…

100 – 200 MHz, w/LNA, w/filter, w/o-3dB-splitter:

100 – 200 MHz, w/LNA, w/filter, w-3dB-splitter:

It seems that the splitter has greater than 3 dB additional loss until up around 140 MHz. The aviation band (118 – 136 MHz) is about 7 dB worse than without the splitter. But that’s it. No other weirdness. I can live with this.

Am much more satisfied now. LNA is directly behind antenna. Have a new experiment to see how solar battery charging works out.

LNA unhappy with 10 uH Coilcraft 0805 chip inductor

Today I finally synced up with my friend Doug and collected from him quantity five Coilcraft 0805 10 uH chip inductors. Tiny things. Had little caffeine today, so by the time I’d returned home I was pretty steady.

Brought the LNA down from roof, opened lid, clamped assembly down to bench so it wouldn’t move, put a drop of 60/40 on one inductor pad, and with my TU-10b tweezer I picked up the part and set it in place, then tapped the one end with the soldering iron. It was harder than I thought; the part weighs nothing and has no surface friction with the tiny bead of molten solder, so it instantly moved on me.

After some re-approaching of the problem, I got the part securely attached. Checked continuity, everything looked good! Lid back on. Connected it to network analyzer, and everything did NOT look good. 20+ dB gain above about 200 MHz. The whole 10-200 MHz output level was badly attenuated, and there were strange artifacts in the low end of the spectrum. Removed the inductor and everything returned to normal. Posted a note to the designer over on gpio.com and am awaiting a response. 10 uH at 100 MHz is 6k  ohms impedance, so it should be fine. The LNA was drawing its typical current (~ 160 mA).

Took another identical  inductor and pressed it down on the pads with a plastic tuning stick, and did exactly the same thing as soon as it made contact. There’s something about that output circuit that doesn’t like the chip inductor.

 

 

LNA mounted – time to test!

To recap: I’ve taken the LNA that I purchased from iseeabluewhale on eBay and put it into a diecast aluminum box (purchased 10 of those from wonderco_buy on eBay as well). The TNC pigtails came from my friend Chris’ stash. The other bits and pieces came from the fossil beds of the garage.

Turned out to not be so tricky to get the thing mounted and connected.

Put it up on the roof behind the FM notch, and powered by 4 NiMH batteries.

First test – sweep 100 – 200 MHz and see what it looks like. Hopefully it looks just like the sweep from last night, just 20 dB higher.

100 – 200 MHz Pre-LNA, with filter, from last night (red peak, green instantaneous):

100 – 200 MHz w/LNA, with filter:

No obvious instability or oscillation. All the signals I can hear, like NOAA weather, Arizona DPS, aviation AM, even the residual signals from FM broadcast, all clear and crisp. My my my. Looks like pretty good fidelity.

Now I’ve just got to get a source of stable dc power to the amp! And I like these little boxes…

Spectrum scanning (again)

Now that the filter setup appears stable, it’s time for another assay of the spectrum around the QTH with the discone.

001 – 100 MHz (old):

001 – 100 MHz (new):

Pretty big difference! And just to check the ICOM demodulator, here’s the same spectrum using the AM demodulator.

100 – 200 MHz (old):

100 – 200 MHz (new):

Low noise floor, more better! Still some strong interference, but livable.

200 – 300 MHz (old):

200 – 300 MHz (new):

So much better.

With most of the big interferers suppressed significantly, tomorrow I will put one of the LNAs in a case and get it up on the roof as part of the lineup.

FM broadcast band notch filter update

Wasn’t able to spend any time on this the past week or so, but today I finally tracked down the pesky problems that I was having with my temporary installation.

I’d damaged one of the original TNC pigtails used to connect to the filter, and that created a sometimes 30 dB additional loss. Also, I finally found a marginal to no-good TNC-f to TNC-f adapter that I was using temporarily to connect the TNC-m connector on the box to the UHF-m connector on the cable that runs from the roof to the shack. I don’t like UHF connectors of any type, but the discone has a UHF-f connection and this cable was originally connected directly to the antenna. Until I finish my next phase of project (getting LNA into a die-cast box as well) I will leave it this way.

Using the ICOM PCR1000 receiver, here’s a plot of 50 to 150 MHz. Pretty serious FM broadcast band suppression!

n7uvqth_pcr1000_50-150mhz

Still a few broadcast stations making it through, but much better than before. The plot below is the one from a few weeks back when I first got the filter assembled into the box.

n7uvqth_pcr1000_fmbroadcastband_filter_in_box_1120sun

 

The following is what it looks like today.

n7uvqth_pcr1000_fmbroadcastband_filter_in_box_1807sat

What’s changed? Certainly the filter/coax assembly is doing a better job of rejecting the FM broadcast stuff, but what’s curious is the new noise floor rise that wasn’t apparent before. That noise floor rise corresponds to the band notch characteristics of the filter, but I don’t know why I didn’t see it before.

Also, the installation needs to be rid of the coax adapters that I’m using while the project is midway. Once I get the LNA into a cast box, then both the LNA and the filter into a bigger cast box, I’ll install N-f connectors on the outside of the big box and will no longer need the adapters.

Finally getting somewhere…

Filter in a die-cast box

Sunday comes bright and early and I decide to put the FM broadcast band notch filter into a die-cast aluminum box.

First, I found in the garage the G112T box I had purchased a long time ago. Measuring somewhat carefully, but not enough, I estimate the spots on the two ends of the box that I’ll have to put 1/2″ holes to install these little TNC-f to coax pigtails.

The TNC-f chassis mount bodies are just about as big as the sidewalls of the box, so aiming carefully is important. However, I miscalculate low on the first hole, and have to oval it just a hair to fit the body of the connector. The second hole I overcompensate, and it’s a little high. But, within 30 minutes I have the case drilled and ready for the filter/coax assembly.

img_4462_sm img_4461_sm

The little TNC coax pigtails came from a buddy of mine – he had a billion of them from some former project.

Before I take the filter off the roof, I measure it one more time while it’s foil-wrapped. Didn’t have a photo of the install from last night, so here it is today.

img_4465_sm

Kinda ugly, no?

Using the Icom setup, it appears a little worse than yesterday night. Could be so for a number of reasons, including propagation, xmtr power output changes between night and day, or the foil moved a bit during the night. Not sure.

n7uvqth_pcr1000_fmbroadcastband_alfoilwrapped_1020sun

Taking the filter down off the roof, I cut off the SMA-f board mount connectors, clean off the excess solder, and prepare the TNC jumpers to solder directly to the board in place of the former connectors.

img_4466_sm

img_4467_sm

The reason I prepared the coax open end as shown in the above picture is apparent in the next photo when I solder the TNC jumpers to the filter board.

img_4470_sm

img_4469_sm

img_4471_sm

Now to install the filter and coax assembly into the enclosure and prepare the sealing gasket.

img_4474_sm

img_4472_sm

img_4476_sm

img_4477_sm

img_4478_sm

The box is almost ready to close up. Don’t want to lose the little screws that are intended to hold down a board inside the case so I install them now.

img_4479_sm

Next, put on the lid and tighten down the screws. Use a compression clamp to squeeze the case closed instead of making the screws do the work. Aluminum strips out very easily.

img_4480_sm

img_4481_sm

All done. Now, since the rooftop cable from the antenna is an N-m connector, and the feed down to the shack is currently a UHF-f adapter, I add those to the case.

img_4483_sm

img_4484_sm

img_4482_sm

Voila! All done. Now, to the roof!

img_4464_sm

Here’s a shot of the discone up on the roof. The thing attached to the chimney is a 2.4 GHz Ubiquti 2.4 GHz Bullet M2 set up as an access point, so I can get Wi-Fi pretty much anywhere around the neighborhood.

img_4485_sm

img_4486_sm

n7uvqth_pcr1000_fmbroadcastband_filter_in_box_1120sun

It does appear that the box is certainly no worse than the foil and at least for a few stations it’s actually improved on the rejection. That pesky 107.9 MHz station is down 10 dB with the box.

Since that wasn’t as hard as I thought it’d be, I need to order a few more of those nice little G112T boxes, or something similar!