Month: November 2017

WSPR Reception 24×7

WSPR reception 24×7 has always been something I have wanted to try. The problem is trying to find a transceiver, computer, antenna combination that will allow this with minimum fuss.

472 KHz Reception

 

Computer

You won’t need a very high spec computer, but if you are leaving it on 24×7 low noise and power consumption will be high on the priority list. A laptop is one option, although they often have fans and may not be noise free, so you may want to consider one of the new breeds of “minicomputer”. Low power consumption, and low noise with many running on 12v. I opted for a second-hand minicomputer, silent running and powered from 12v. It uses the Intel Celeron J1900 with 4 cores and I added a 128G SSD so it boots in 3 to 5 seconds. These are good value and should provide a reliable machine, with a very small desktop footprint.

Antenna

If you looking to cover multiple bands then you need a broadband receive antenna and this typically doesn’t work well on a simple unmatched G5RV or doublet antenna. I completed some receiving tests using my doublet and a Wellbrook and found the loop outperformed the wire antenna significantly below 5 MHz. You can read more about receiving loop antenna on this page. George M1GEO has provided a very interesting article and instructions on how to build a low-cost Wellgood loop on this page. The Wellbrook loop I use seems especially good at 136 and 472 KHz, providing some interesting spots on these bands. The antenna is shared with my online SDR providing connectivity to the ELAD and Kiwi via a 2 port antenna splitter.

Transceiver

I use the ELAD SDR, as its very low power consumption, and I can CAT control the band changes to suit the time of day.  The radio is connected via USB to the PC running Joe Taylor WSJT-X program.

The transceiver draws around 500 mA on receive and the Mini PC  around 600mA at 12V. I have used a 12v SMPS designed as a computer power supply, its rated at 5A and runs cold.

 

In the last 24 Hrs

Receiver antenna and band changes biased towards MF and LF

Typically adding 1,000 spots per day

150 spots on 472 KHz and 23 on 136 KHz

I hope to add TX soon, using 200mW from the Ultimate 3S beacon transmitter

 

50, 70 and 144 MHz in one beam.

I have always enjoyed taking part in the UKAC series of contests, they are very busy and ideal for portable operating in the summer months.

Not so much fun in the winter, but the chance to operate from home required a beam. I have tried to take part with a vertical co-linear, but the crossed polarised loss and my limited takeoff resulted in very poor results. The RSGB has recently added an FM section to activity evening, but while this is interesting to achieve any distance SSB is the mode.

Here is a typical portable setup, this one was in December!

I operate the Icom 7100, and this can facilitate 50, 70 and 144 MHz in SSB, so was looking for a beam that could do all 3 bands. DK7ZB has a design on his website that covers all 3 bands, with a very short boom. Yes, it’s a compromise antenna, but working on the principle it’s better than nothing!

 

The boom is just 1.2m long, and it is a single 50 Ohm feed.

The design is detailed on Martin website, the antenna is a 2e on 50 and 70 MHz and 3e on 144 MHz

I found the antenna very helpful at my QTH, allowing a small discreet 3 band yagi to be installed and me to take part in the UKAC contests. Here you can see the antenna around 7m high.

Coax Cables and Associated Losses

As a newly licensed amateur, one of the points I found hard to grasp was feeder losses. While it was explained to me that feeder cable had losses, it was sometimes hard to visualise what this meant in the real world.

The maths can be a little scary, and so in this article, I have looked at some real-world examples.

So we all appreciate that coax has losses, and we understand these increase with frequency and have a direct relationship to the length of the coax. Coax of course also has a maximum power handling rating, although this isn’t applicable to foundation licence candidates it’s worth considering this as you work towards a full licence and the ability to run 400w.

The amount of RF power (and received signal) will always be less than we put in, it’s worth taking a moment to consider that this applies to both transmit and receive signals as losses work both ways. The addition of a Low Noise Amplifier at the masthead will help to offset the receive losses, but it will do little for your transmit power. Often we say that’s fine, I will just use more transmit power, but that’s not always possible unless you have linear amplifiers to hand.

At HF (below 30 MHz) the losses are not significant, and we can usually opt for RG58 or RG213 coax, but as we move up the spectrum 144 and 430 MHz present a different challenge. The quality of your coax now becomes a significant factor in how your stations perform, and investing in good quality coax will often provide a better return than spending more on your antenna.

Let’s assume we have a typical coax run of 30m (100ft in old money) and we wanted to review the actual power presented to the antenna for various coax choices.

In this example, we have a radio with 10w (Foundation Licence) out and will be using 30m of coax. So for each frequency, we can now read off how much power will actually reach the base of the antenna.

Power 10w 30 MHz 50 MHz 146 MHz 440 MHz
RG-58A/U 5.6w 3.9w 2.46w 0.9w
RG8(mini8) 6.3w 6.16w 3.54w 1.54w
RG-213 8.7w 7.4w 5.24w 3.1w
LMR-400 8.5w 8.12w 7.08w 5.36w

The same figures have been calculated with 50w (Intermediate Licence)

Power 50w 30 MHz 50 MHz 146 MHz 440 MHz
RG-58A/U 28w 19.5w 12.3w 4.5w
RG8(mini8) 31.5w 30.8w 17.7w 7.7w
RG-213 43.5w 37w 26.2w 15.5w
LMR-400 42.5w 40.6w 35.4w 26.8w

So for every pound invested in your coax, performance will be increased on both your transmit and receive path. The actual coax you choose may well be influenced by the route and the bend radius, large diameter coax doesn’t bend very well.

Just to complete the picture, the last example is using 400w (Full Licence)

Power 400w 30 MHz 50 MHz 146 MHz 440 MHz
RG-58A/U 224w 156w 98.4w 36w
RG8(mini8) 252w 246.4w 141.6w 61.6w
RG-213 348w 296w 209.6w 124w
LMR-400 340w 324.8w 283.2w 214.4w

The figures have been calculated by looking at the feeder loss in dB/100m. These figures are a guide and provide the typical power (loss) seen for these coax types. The actual figure may vary, I have not considered coax connectors and adaptors as the quality and losses vary, so your measured RF power is likely to be even lower as the losses increase.

In selecting your coax you may want to consider the dB loss figures quoted by the manufacturer, the lower the dB the better in this example.

loss/100m (dB) 30 MHz 50 MHz 146 MHz 440 MHz
RG-174 16.5 19.8 39 75
LMR-100A 11.7 15.3 26.4 46.8
RG-58A/U 7.5 12.3 18.3 31.2
LMR-200® 5.4 6.9 11.7 20.7
RG-59 x 7.2 x 22.8
RG-8X 6 6.3 13.5 24.3
LMR-240 3.9 5.1 9 15.6
LMR-240 Ultra 3.9 5.1 9 15.6
RG-8/U FOAM x 3.6 x x
RG-213 1.8 4.5 8.4 15.3
RG-214 3.6 4.8 8.4 15.3
LMR-400 2.1 2.7 4.5 8.1
LMR-400 Ultra 2.1 2.7 4.5 8.1
DRF-400 2.1 2.7 4.5 x
Bury-FLEX x 3.3 x x
9086 x x x 8.4
9913 2.4 x 4.5 8.4

And lastly maximum power rating for typical coax types.

Max Power Handling 30 MHz 50 MHz 150 MHz 450 MHz
LMR-100A 230 180 100 60
RG-58U 400 300 160 80
LMR-200 1020 790 450 260
RG-59 500 400 250  x
RG-8X 350 280 150 80
LMR-240 1490 1150 660 380
RG-213 1800 1200 620 300
RG-214 1800 1200 620 300
LMR-400 2100 1700 1000 550
DRF-400 3300 2570 1470 830
9913 2200 1700 900 450

 

The following online resources will help you calculate losses.

dB calculator

Coax attenuation chart

Coax type v loss

 

© 2015 Dave, M0TAZ