AmateurRadio.com

So you’ve played with DSTAR enough that you’ve decided you want to host your own repeater. Well congratulations! Welcome to one of the most challenging and satisfying activities in your ham radio “career”!

Here’s what you’ll need if you want to build a DSTAR repeater.

1. Antenna
2. Feedline
3. Lightening protection (suppressor, in addition to a proper ground system)
4. Duplexer (a flat-pack mobile unit will work if you’re in a low RF environment. If there are other transmitters around, you’ll want larger cavities – a band-pass/band-reject unit.)
5. A repeater site – as high as you can get, with easy access for maintenance
6. Internet access – including a public facing ip address so users can route directly to you from other repeaters
7. Power supply – 12V at whatever amps you’ll need
8. Miscellaneous cables…all good quality!

As a quick side note, all of the principles for analog repeaters applies to digital systems. Checkout www.repeater-builder.com for tons of good information.

Phew. Now that you’re done with the antenna system and internet access, you’ll need to make a decision. Are you going to go with the ICOM system, or a home-brew system?

For an ICOM system:
1. Radio module for the band you want to be on ($700 for UHF)
2. Controller module ($850)
3. Computer running Linux to run the gateway software (figure $300 for a solid system)

That’s $1850 in addition to items 1 through 8 above.

The other option is a home-brew system. I’ve built two of these already – one from Kenwood radios, and one from Motorola radios. Either of these requires access to programming gear/software, so you may have other costs you need to consider.

For a home-brew system built on Motorola radios:
1. 2 CDM 1550 UHF radios (one for TX, one for TX) – $300 from eBay
2. Raspberry Pi with SD Card to run the G4KLX gateway software ($50)
3. DVRPTR modem – http://dvrptr.net/ ($120)

For the CDM radios, you can’t run them at 100% power – these are mobile radios, and they are rated at 50% duty cycle or lower at full power. I’m using 30 watt radios at 10 watts. The transmitter doesn’t seem to mind this power setting, even when run for 2 hours continuously. Because of the acknowledgement packets that are sent after user transmissions, duty cycles easily get 100% during normal DSTAR use. Hold a net, or a long QSO, and you’ll find your transmitter melted if you try to run it at too high of a power setting.

You can add a power amplifier after the transmitter if you need more power. I’ve not found this to be necessary with the proper antenna and site. If I can hear the remote units, they can hear me. More power hasn’t been necessary.

I’ve also had success with a Kenwood TKR-820 repeater. But….programming these for me is harder. Alignment is a bunch of coils and takes some time. They have a built-in power supply. You really need to narrow-band the units, as that’s what the users’ radios are expecting. It will work wide-band, but it won’t work as well. The system needs to be narrow on both the repeater and user side.

Michael Brown, KG9DW, is a regular contributor to AmateurRadio.com and writes from Illinois, USA. Contact him at [email protected].

FlexRadio Systems was born out of the dot-com bust in the early 2000’s. Founder Gerald Youngblood K5SDR didn’t really expect it to go anywhere. Boy was he surprised. He told the story at the 2014 ARRL/TAPR DCC Saturday Banquet:

Gary Pearce, KN4AQ, is the host of HamRadioNow.tv. If you enjoy this and other HamRadioNow programs, help keep them 'on the air' with a contribution. Contact him at [email protected].

There's been a lot of discussion lately on the Yahoo Groups ndblist regarding the "low-noise vertical" (LNV) and it's seemingly excellent performance. Originally described by Dallas Lankford as a good performer from LF to SW, ndblist member, Phil (KO6BB), recently refurbished his earlier built 'LNV', but this time with better feedline and appropriate ferrite cores for the antenna's matching transformers. Some of his description appears below.


To recap. I put the LNV up last spring to overcome the bad IMD products
from local BCB stations I was seeing in the LF region when using the
Roelof Active Whip located about 36 feet AGL. The low noise vertical is
... about 30 feet of antenna, set at roof-line level in this mobile home. As I wasn't sure how well the antenna would perform, I first made it a "Zero Dollar" project, using items I had on hand. Those items included two toroid cores salvaged from a defunct computer PS. I figured that since the supplies operate in the kHz range (as witness what a dirty supply will do to your LF reception), they would be suitable for at least a trial run of the antenna. The balanced feedline was some CAT6 cable I had on hand.

The antenna was a great success, because while it had much lower signal
output than the active whip, it also had ZERO IMD from the BCB stations,
and also less local 'junk' (read noise). The tunable pre-amp I use more
than made up for the lower output of the antenna, after all Signal/Noise
ratio is EVERYTHING in this hobby, NOT how high you can make the "S"
meter read.

The central valley summer heat (often in the 100's) took it's toll on
the CAT6 feedline outer jacket insulation, and while it still seemed to
work OK, I figured that it wouldn't be long before water started to get
into the line and probably degrade it in rainy/foggy weather.

Anyway, I went ahead and ordered the proper toroid coils I needed along
with 25 feet of nice 300 Ohm foam twinlead, and got a couple plastic
boxes to put it all in and made the toroid units. While I was at it ordered
two Amidon FT193-J toroid cores to complete the LNV the way I REALLY wanted to.

Today I installed it all, putting a heavy twist in the feedline to try
to reduce any stray noise pickup on the balanced feedline. I'd say
probably not likely but why take a chance.

OK, here are the results. I took signal level readings of eight 24/7
stations, both before and after changing out the wiring/baluns. The
bottom line is, the new antenna IS an improvement in the NDB range,
tapering off slightly at the high end of the broadcast band. Yeah, it's
'only' a couple "S" units at it's best, but when you're digging for that
weak NDB even 1 "S" unit is a LOT! I'm going to 'assume' 6dB per "S"
unit as I have calibrated the "S" meter of the R-71A receiver.

NOTE: This is 'fuzzy' math, don't take them as 'exact' on the dB readings.

FREQUENCY BEFORE AFTER DIFFERENCE
203 TCY S2 S4 2 S units (12dB)
205 COT S3 S5 2 S units (12dB?)
344 FCH S9+7 S9+15 (8dB)
374 LV S6 S7 1 S unit (6dB)
580 BCB Sta S9+35 S9+38 (3dB)
770 BCB Sta S9+32 S9+32 No Change
880 BCB Sta S9 S9 No Change
1450 BCB S9+10 S9+5 (-5dB)

SO, it looks like the antenna is definitely an improvement where I'm
REALLY interested in it (the NDB band). I could have probably tailored
the toroids for maximum performance, but just used the 81:9 turns ratio
on the outdoors (antenna) and 9:9 on the indoor unit as I'm FAR too lazy
to run up and down the ladder to remove the toroid box, change turns and
retry it again!!!

Some additional notes.

NOTE 1. I have three ground rods dedicated to just this antenna, two 8
footers and a 4 footer. While I was playing with the antenna taking
readings AFTER the work, I disconnected one of the 8 foot rods to see
what effect that had. Signal levels dropped approximately an "S" unit
across the board. So GOOD grounding on this antenna does make a difference!

NOTE 2. I'm NOT exactly sure why it happened, but after the antenna
work here, there was even LESS "local grunge" in the background than
before, even with the stronger signals, making for even better copy on
weak ones than I otherwise expected. . . It DOESN'T make sense to me,
but then, antennas ARE the magic art.


It appears that the grounding plays some importance in the performance of this "non-resonant" aperiodic antenna and the fact that it is non-resonant on the frequencies of interest likely also plays an important part in its good S/N performance.

Several years ago I noticed something similar. My own 10' tuned air-core loop made an excellent receive antenna on 160m, even though the loop was tuned to around 300KHz! Although signal strength was several S-units below my transmitting antenna, the loop was extremely quiet and weak signals were much easier to copy ... In fact I often heard signals on the mis-tuned loop that I could not hear on my resonant half-sloper radiator.

Another ndblist proponent of the low noise vertical is John, in Colorado, who employs three ... one of them a great-looking tilt-over version. The tilt-over is nicely demonstrated in his short you tube video below.


The antennas are also used in combination via his Quantum Phaser, when DXing the broadcast band. The excellent phasing results can also be seen in his short video, while using a wonderful, like new,  Hammarlund SP-600 JX.


Dallas Lankford's original article may be found here, while an earlier more encompassing discussion will be found here. A third Lankford article, discussing 'Signal To Man Made Noise Ratios' and comparisons of various receiving antennas, also makes for interesting reading.

Perhaps the 'LNV' might be the antenna you're looking for to boost your LF/MW reception.

Steve McDonald, VE7SL, is a regular contributor to AmateurRadio.com and writes from British Columbia, Canada. Contact him at [email protected].

YouKits has introduced a new product into their line of amateur radio transceivers, kits and accesories.
The latest is the DP-1 QRP Digital Power and SWR Meter.

• Assembled and ready to use.
• Power consumption: 30mA
• Size: 60x100x37mm
• Can install our 18650 battery pack (option)
• Can power other radios with internal battery pack.
• Power measure: 10mW-25W
• Frequency covering 1-30Mhz
• Only $129

Shipment will be started on 05/Feb

http://www.youkits.com/

Fred Lesnick, VE3FAL, is a regular contributor to AmateurRadio.com and writes from Thunder Bay Ontario, Canada. Contact him at [email protected].

See http://www.phonestack.com/farhan/minima.html

This is the latest project from Ashaar Farhan. Component cost is said to be less than $100. This is based around a Si570 sythesiser and a programmed Arduino micro-controller IC. It looks a simple to duplicate rig covering up to 30MHz. It is the successor to the BITX rig I think. The IF is 20MHz. If you only want 0-15MHz or 15-30MHz (i.e. not both) the rig get even simpler.

As it stands it produces 1W pep but it is easy to add a further PA. 

Although a kit of parts is available, I am not aware of a full kit with enclosure and a PCB being available as is the case with the BitX from Hendricks Kits.

Roger Lapthorn, G3XBM, is a regular contributor to AmateurRadio.com and writes from Cambridge, England.

Buying crystals for specific frequencies is now getting very expensive. There may be a newer alternative.

See https://aa7ee.wordpress.com/2015/01/12/a-crowdfunded-si5351-breakout-board-from-jason-nt7s/ .

This synthesised solution allows any frequency from 8kHz to 160MHz to be generated.

Roger Lapthorn, G3XBM, is a regular contributor to AmateurRadio.com and writes from Cambridge, England.

Christmas seems such a long time ago and one of my presents was a Feature Tech AW07A HF-VHF-UHF Antenna Analyser which I have finally been able to try it out.


It is about the size of a thick paperback book and is a powder coated steel case similar in style to that used by MFJ equipment, indeed the MFJ-266 analyser appears to be a re-badged version albeit for a lot more money than this unit can be purchased.

It can be powered by batteries fitted internally or by an external supply and is supplied with a power cable for connection to an external supply, mine was white/black rather than the normal red/black cable. It has a N-Type socket for the antenna and comes with two adapters for PL259 and BNC connectors.


It has a power button near the external power socket, two buttons on the top select HF and VHF/UHF operation and two other buttons marked UP and DOWN to select operating mode and/or the frequency band being used. Unfortunately one thing it doesn't come with is a manual but a copy can be downloaded from QSL.net or a slightly different version from the manufacturers website. But I actually downloaded the manual for the MFJ-226 has it is much more detailed.

The front panel decal and manual state it can be run from 10.8-12V, in fact the manual states it should ideally be less than 12.5V and no more than 13V. While doing some research I found the reason for this limitation hidden away on this aliexpress webpage "Avoid higher than 13V power supply circuit for the UV segment may be damaged due to excessive power dissipation." So this would seem to rule out using a standard 13.8V power supply.

It can be fitted internally with eight AA batteries and this is the way most people would use as it offers portability. Removing four screws allows access to the battery compartment and the internals electronics seem well built.


It takes eight AA batteries, in two boxes. The battery boxes have lids secured with a small screws and are fixed to the case using simple sticky pads, while secure at the moment I can imagine in time the adhesive could dry-out and become unstuck leaving the battery boxes loose inside the unit.


The display is a simple two line LCD with an optional bright back light which can be turned on during the power up sequence. The display shows the battery or supply voltage and pressing Down puts the unit into a frequency counter mode. Pressing Up puts into the antenna analyser mode.


In the analyser mode it is a simple case of selecting the HF, VHF or UHF mode. VHF works from 85-185MHz, UHF is 300-390MHz, the HF is split into six overlapping bands A: 1.5-2.7 MHz B: 2.5-4.8 MHz C: 4.6-9.6 MHz D: 8.5-18.7 MHz E: 17.3-39 MHz F: 33.7-71 MHz selected using the Up/Down buttons.

Turning the vernier  tuning knob adjusts the generated frequency the antenna is being tested against. I connected the analyser to my 2m YAGI antenna and turned the knob to find the lowest SWR


The manual describes what is being displayed (on UHF just the SWR is shown)

“139.763 MHz” is the frequency
“V “is the band (A,B,C,D,E,F in HF, V in VHF and U in UHF)

The bottom row shows the complex impedance Z = R + jX, so on this screen 

“41” represents R = 41 ohms the resistive component
“18:” represents the reactance component value, jX = 18 ohms
“45” is the overall complex impedance magnitude Z = 45 ohms
“1.5” is the SWR value

As you can see for a 2m antenna something isn't quite right! The antennas were down due to last weeks strong winds so I was taking the opportunity to do some maintenance and tweaking of the 2m antenna since I'd seen an increase in the SWR during recent UKAC contests. I had suspected feeder issues, possible water ingress but I tried a dummy load at the antenna end but that read as expected (Z=50ohms) and metering the continuity of the feeder showed no issues, it just seemed to be resonant at too low a frequency.


The analyser confirmed what I'd observed with a normal SWR/Power meter a higher than desired SWR in the middle of the SSB section of the 2m band.


Unfortunately I was unable to get it any lower than 2.5 and most adjustments seemed to increase the SWR.  For peace of mind I double checked the analyser by swapping the feeder on to the 2m/70cm collinear and that was spot on


again I double checked the SWR readings back in the shack using the normal meter


While I try to sort out the antenna issue I can say the analyser seems to do its job well. The tuning knob is a little twitchy and has a bit of play which makes setting the frequency accurately a little harder than it should be but hopefully that might improve with use.

The unit also has other functions none of which I have used yet but it is bonus to have some useful test functions available in the shack.

The AW07A can be used as an inductance/capacitance meter by powering it up with the U or D button held down. The inductance or capacitance of a component fitted across the antenna socket is then displayed and this can be done for any test frequency by selecting the band and turning the tuning knob.

As I mentioned earlier the unit can also function as a frequency counter that can measure signals between 1 and 500 MHz and can be used to give an indication of relative RF field strength. A signal source or an external antenna that yields a usable signal level may be connected to the analyser’s antenna jack. The usable signal range is quoted as -20dBm (30mV)  to +10dBm (1V). Note that the display reading is a RMS value.

Obviously in the antenna analyser mode the output which is approximately 2V in magnitude can be used as a signal source, with 20dB of second harmonic suppression. 

The MFJ manual goes into some detail of how this all works and how to use the analyser for a number of common tasks such as checking baluns, making 1/4wave stubs or measuring velocity factor of coax.

While the AW07A has some obvious shortcomings and may not be a precision device I am impressed with it and what it can seemingly do. It is shame about the lack of a manual but I am not sure getting one is justification for the premium price of the near identical MFJ unit.
Andrew Garratt, MØNRD, is a regular contributor to AmateurRadio.com and writes from East Midlands, England. Contact him at [email protected].