NE-FL D-STAR System

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Archive for category Test Equipment

Adjusting IF Filters – the WYSIWYG Way

Aug 30

Posted by mikelee in HF Antennas and Operation, Kit Construction, Test Equipment | No Comments

I’ll bet that most of us have never actually known how to adjust or “tune” the IF filters in our radios, regardless if HF/MF or VHF/UHF. All I was exposed to was to tune for best match to my EAR – if it sounds good, then it’s good enough..!!

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Although true – and certainly everything has to (eventually) pass to our ears, there may be a better way to be able to understand how filters respond – and to take advantage of their characteristics in ways that we’ve never experienced in the past. Also take into consideration that the new digital modes will be able to “hear” even below the noise-floor  - so the ear may no longer be a factor in the near future (or current). I used the following technique when I needed to adjust the bandpass characteristics of the Elecraft K2′s IF filters. It was quick, easy, highly visual and very accurate.

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The technique starts with injection of broadband, but stable (consistent) noise into the front-end of a receiver. For this, I used the Elecraft N-gen – an inexpensive, yet very useful tool that provides a noise signature that is within 3db from 100khz to 500mhz, it’s useful for all our radios to lower-UHF. The unit comes as a kit (typical Elecraft) that is very easy to assemble and has a single ON-OFF switch and a BNC-F connector for it’s output. It’s stand-alone, powered by a single 9V battery. You simply connect the N-gen using a short BNC M-to BNC-M cable, or a simple BNC-MM adapter works nicely as well. Turn the N-gen ON and you have a noise source being injected.

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The next part requires a laptop with a microphone port to the sound card, as well as some software, as we’ll now be looking at the AUDIO that results to the external speaker port of the radio (an Elecraft K2, in my case). Fortunately, most radios have standardized connectors – most HF radios use 1/4″ phono plugs, while more compact radios use the 3.5mm stereo plug. Coincidentally, most laptops also have a 3.5mm stereo receptacle for mic-INPUT (as well as output), so it was a simple case of having a short 3.5mm male-to-male stereo cable to make this test between my MacBookPro and the Elecraft K2 (about $4 at Fry’s or other similar stores).

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Software for the Audio Spectrum Analyzer comes in all flavors, as well as prices. Although we could have used many VERY expensive tools destined for the professional sound industry, there are a number of Freeware packages available.

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The technique is as follows :

  • Connect the audio OUTPUT from the radio, to the sound card INPUT (Mic-input in most cases) of the laptop.
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  • Start Spectrogram or iSpectrum, depending on your hardware platform.
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  • You should see a representation of the radio audio-output on the screen – if not, switch to the other channel (left, or right).
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  • Once you’re able to see the signal displayed as a moving graph on the screen, narrow the bandwidth of the audio sweep from a low of ZERO, to a high of about 2.5 or 3 khz. This will focus our analysis on that portion of the usable radio audio spectrum.
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  • Now start adjusting a single parameter of the current IF filter and watch the response on the Audio Spectrum Analyzer – you’ll see the noise move from left to right. If the filter is operating, you’ll see cut-off either on the left-side (low cut) or on the right-side (high-cut). In some cases, you might see both sides cut-off, signifying that you’ve engaged an IF bandpass filter.
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  • Okay… now we understand cause-versus-effect. We’ve made a change thru one of the controls, then SEEN the effect of that change to the audio spectrum. Remember the N-gen generates broadband noise that is quite uniform across the spectrum of 100khz to 500mhz – to within 3db (about 1/2 of an S-Unit), so what you see, is pretty-much what you get (remember that the human ear can only distinguish about a 4db change in sound volume – best case).
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  • Time for some real alignment – I’ll use the  8-pole CW filter that has a bandwidth of 400hz. In this case, we want the (passed) noise to be dead-center on the our SideTone frequency (600hz in my case) so I’ll set a marker at 600hz. We want the noise to be centered here – with equal fall-off on both sides of the 600hz marker.
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    Let’s start with a wider filter, so that we “zoom” into the target bandwidth – here’s the progression :

  • Above is actually of a fairly wide-band CW filter (1.0khz).. 


    Above is from a 400hz wide filter – notice that the skirts only go about 200hz on either side of the 600hz marker line…

  • SSB filters (or anything non-CW) have a broader bandpass, so instead of aligning to a center frequency like in CW (at the side-tone frequency), we normally try to align the filter to be centered BETWEEN two frequencies (low-and-high limits). The standard objective is to get as much of the received noise to be within the low and high cut-off points as possible – and not have some of the signal ‘roll-off” either the high, or the low ends.
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    Above : an example of an SSB filter that is biased too far to the low-side – while this might be good for low frequency fidelity, it will compromise high frequency response – an area where most of the consonants are in the English language. 


    Above : a better aligned SSB IF filter that keeps most of the signal within the limits of the filter bandwidth.

A Wonderful Power Supply – the Tek 280

Jul 19

Posted by mikelee in Kit Construction, Test Equipment, Tools | 1 Comment

All good electronics projects eventually require a power supply – and if you’re building a kit (like seems to be my funk nowadays), having access to something more than a standard Astron is sometimes more than handy – it’s essential. There are many times when measuring small changes in current (in terms of milliamps) is required as you add options, make changes to circuit boards, or enable options on the radio (like the DSP, which consumes a bit of power). Even measuring the additional current draw of an Auto-Tuner in the radio would be barely noticed on an Astron with analog meters which measure in amps (and very inaccurate, at that).

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The TEK 280 is not new to me, or to my lab – but it has been sitting faithfully in my Las Vegas lab for nearly 5 years without use, so I thought it was time for me to take it  to Florida, since that seems to be my primary residence now. As I de-installed the unit from the lab, I got a renewed appreciation for why this is such a nice unit:

  • it’s a triple power supply – three independent outputs, but with a twist (see below)
  • there’s a dedicated 5v output that has capacity for 3A
  • there are two other, independent outputs that are both Variable in Voltage, and Variable in Current (if current limiting is turned on). Each of these outputs can be adjusted from 0.1 to 32.0 volts and current to a max of 2A. Certainly not a high-current supply, but it supplies and measures to within .01v and 10mA
  • Both of the independent supplies can ganged, so if you need PLUS and MINUS 12vdc, you can do it with this unit.

Why all the fuss about this unit (or ones similar)..??  Have you ever needed to monitor supply voltage AND the current draw of a circuit or device at the same time – down to the tens of milliamps..?  If you’re like me, most of the time I’d need to put the Fluke in series with the positive side of the supply and measure the current consumption – a hassle given all the wires and cables. With this unit – it’s all displayed on the front panel. In fact, if you’re trying to compare two identical circuits, you can supply both with this power supply and monitor current on each unit independently.. very convenient.

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I bought this unit new about 8 years ago. Fortunately, I had a client that was paying for some R&D that I was performing, so the $890 price tag was a non-issue, but still worth every penny. Fortunately, it’s now considered obsolete, and I see a number of units listed on eBay for about $300 in (apparent) decent condition. If you’re in the market for this type of Lab-grade, low-current, high-function, triple supply – this one is the bomb..!!

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Elecraft K2 Construction

Jul 7

Posted by mikelee in Kit Construction, Test Equipment | No Comments

Wow… Can I say it again …..?? WOW..!! .

I just finished the base-model Elecraft K2 HF Transceiver kit with the Battery Module – and it is a beauty..!!   Beautiful parts, beautiful circuit board and beautiful instructions.. This is Heath-kit to a whole new level (and a lot more complexity). But fortunately, PIC micro-controllers are here to stay and they really simplify the diagnostics, configuration and alignment necessary for this unit.

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Total construction time took 32 hours – from unsealing the first of the plastic bags of parts to final alignment – your milage may vary, but I went very slow and double-checked parts values and positions before soldering. There are a couple of things I would recommend, if you were to consider this project:

  • you MUST be proficient with a fine-tip soldering iron, soldering in a (relatively) high density environment,
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  • you MUST be patient – this is NOT a single night or weekend kit (unless you have a holiday in there),
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  • you SHOULD inventory each bag of parts – and verify against the parts-list. This is a tedious process, but has paid off for me in the past. On the K2, it is a bit more difficult, since there is an RF-A and RF-B bag of parts for the RF Board – and the parts list doesn’t specify by bag contents.
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  • you will benefit from having a sorting tray, or a place to put small capacitors of identical value – so that you’re not constantly searching for parts. I used a simple plastic storage case from Home Depot that has removable dividers – the width of the compartments is exactly the same size as a standard business card, so I used my ARES cards to indicate the value of the component in the compartment (like 473, 104, 102, etc – see picture). Even with this, I always physically verify the component value before installation, in case the part was mis-sorted.
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  • you will benefit from having an LCR meter, specifically to test and verify the value of small monolithic capacitors – some of the lettering is difficult to real even with 4x reading glasses, I use the BK 879B – and excellent meter of (relatively) reasonable cost. This might be an excellent unit for a club-purchase, since very few people can justify the purchase for a single individual (your usage would be measured in MINUTES per month :D ) . Borrow the unit from the club, identify all the components you have in the kit while sorting them into the parts tray(s) and return the unit…!!

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  • you should have a desoldering tool, because you WILL make mistakes. I mis-installed the Final Amplifier transistors and had the bodies facing UP (toward me) on the bottom of the board (which was incorrect) – when the bodies should have been facing DOWN. I only noticed this when trying to put the bottom cover back on (it didn’t fit) – and only THEN looked at the instructions again and noticed that they were installed incorrectly. Okay, this would have been messy, trying to desolder the three pins of each heavy transistor with just a Solder Sucker and Solder Wick – but the Hakko 808 came to the rescue..!!  Three “sucks” per transistor (E, B, C) and the component nearly FELL OFF THE BOARD..!!  WOW.. I continue to be impressed – HOURS of frustration saved, not to mention the recovery of hard-to-replace parts (either costly, or you have to wait for UPS/USPS).
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  • If you are contemplating purchase of the Hakko 808, I would HIGHLY recommend also purchasing the Hakko 633, which is the Holder and Stand for the 808 ($20.70 at hmcelectronics.com) – it securely holds the unit and prevents it from falling off the table or onto other valuable tools. Pictures of both are below :

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  • A very fine tipped soldering iron that is ESD-safe is essential – no Weller GUNS allowed on this project. I use the now discontinued Metcal SP-200 which has ceramic heating elements and is ESD safe, but there are many units out there nowadays for a much more reasonable cost.
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  • GO SLOW – this is supposed to be FUN – and it will be if you just take your time. The manual is full of great in formation about the building process, but also about the design of the radio and the firmware that controls it. All great opportunities to LEARN while you build.
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How does it perform, you ask..?? According to my preliminary tests after initial alignment, I’m seeing MDS (Minimum Discernable Signal) of about -100dbm or better and max output power on all bands in excess of 12-15 watts (MORE than enough for QRP as well as driving the 100w amplifier which might come later). This little radio plays the fiddle like nothing I’ve see so far..!! . Still have much to build – including the : Noise Blanker, 160m module, DSP Filter module, Auto Tuner, I/O module and SSB module. What a JOY to re-discover building kits and seeing a bag of parts transform into a beautiful, top-notch instrument. THANK YOU Elecraft for bringing back this important part of the hobby ..!! .

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Following are pictures that I took during the construction process :


Above : my sorting tray for Capacitors


Above : the completed Front Panel module – pre-testing


Above : the completed Control Board


Above : RF Board – Synthesizer and filters done


Above : start of integration and getting ready for testing


Above : going thru the Alignment steps, one-by-one


Above : testing – the K2 has a number of built-in test facilities

A WONDERFUL Ham Club Meeting..!!

May 15

Posted by mikelee in ARES Training, D-Star Users, Test Equipment | No Comments

I had the privilege of going to the monthly meeting of the Flagler Palm Coast Amateur Radio Club yesterday – the largest and oldest club in the area with a legacy that spans more than 25 years. But as in all organizations, sometimes length of operation may not be an advantage if things remain stagnant and the members don’t constantly embrace change and push-the-envelope – after all, Ham Radio is a contact sport which is always changing in order to support the world around us (as evidenced by the transition from VHF/AM to FM, the creation of Packet radio by the TAPR organization, WinLink, etc).

But what impressed me the most, was the group itself – some old-timers who have been in the club since the beginning, some folks like me who are newbies and lots of folks in-between who thirst for knowledge, try new things, strive to serve their community and focus on bringing honor to the Amateur Radio Community.

Let me give you some examples, since I believe that this combination of attributes is a formulae for success for all Amateur radio organizations:

  • Thirst for Knowledge – FPCARC has a training program each month that tackles a subject which is relevant to today’s Amateur and is taught by an industry expert. This month, the topic was on Impedance (a super technical and often misunderstood subject) and was taught in a show-and-tell environment by Bill Schwartz (WS1C), a 40+ year veteran of the TV Broadcast industry and Director of Engineering at the PBS affiliate in Daytona Beach. Previous instructors have included a well-known engineer of RFID devices – but in all cases, they teach by SHOWING, not just by talking – no formulas, no math, no brain twisters. Yesterday’s talk about impedance used the AIM 4170 impedance analyzer from Array Solutions ($550, so affordable for a club to acquire and “share” with the members) and was all about looking at graphs which visually demonstrate the correlation of resistance and reactance, over a frequency domain (see picture below). This visual approach keeps club members engaged and provides much more information than working thru formulas….

    (     Click for larger view)
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  • Try New Things – the FPC club has been the first club to conistently and fully embrace new digital technologies in the past such as Packet and most recently with D-Star, while others just poo-poo the modes. In fact, when we first introduced the concept of D-Star repeaters in the NorthEast Coast of Florida, FPCARC members were the first to embrace the concept and over 15 people in the club actually purchased D-Star radios on the promise of repeaters-to-come. A great leap of faith, to be sure. Today, they comprise most of the D-Star community in Palm Coast, with counterparts in the counties to the north and south from Jacksonville thru Daytona Beach.
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  • Strive to serve our community – WOW.. FPCARC is hitting a home run in this area. They hold their meetings at the Public Library (even though they have easy access to the Emergency Operations Center) so that they are in full view of, and noticed by the general public due to the high traffic area of the Library. This gives them some other opportunities as well – aside from the normal HamCram and VEC testing. They recently started a program of training of Home-Schoolers (the Imagine Schools), as well as other students with the goal to earning their Amateur Radio licenses. They will use the library to convene the regular sessions, giving them even more exposure to the public. The expectation is that students will get licenses, thereby getting them into the Amateur Radio rolls at an early age – with the possibility of their parents also getting their tickets.
    ..The club is also looking to have a mini-Field-Day at the Library’s outdoor Gazebo which is large enough for an operation of about 6-8 people, with easy access to trees that can ben  supports for wire antennas. We’re thinking of also bringing EMCOMM-1 to each of the events, so that the students can see a fully equipped mobile communications center.

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    This focus on the students gives us an infusion of young, current thinking into the hobby. For all of you who thought that Packet and the higher-speed digital modes like WinLink and D-Star – think again..!!  The new generation of Amateurs are fully-digital in their lifestyle – and they will expect (or PUSH) Amateur Radio to be consistent with that mantra. Hang on to your seats – the future is yet to come – and it will approach with a speed we’ve never seen before.
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  • Bring HONOR to the Amateur Radio Community – this group exudes “class” – they are a group of salty old(er) guys who have all “been-there, done-that” – who have accomplished much in their professional careers and who have no need or desire to “strut-their-stuff” and be the loudest noise in the crowd. In the words of one prominent member, “all of us have run a business, managed large groups of people, or been responsible for multi-million dollar budgets”. In short – these guys have earned their wings – not been given a cheap set of plastic wings from the flight attendant. The members are known to the County Emergency Manager, who holds them in high regard. The current president of the club worked with the “Quite Professionals” (US Navy Seals for the uninitiated). Others members were former executives of companies like Bell South and the NY/NJ Port Authority amongst many, many other marquee companies that are household names.
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    As result – these fellows make good decisions. In the midst of a poisoned atmosphere of lies and accusations by others, these guys hold their head high, their ears open, their tongues in-check and subscribe to the fact that every word that is uttered – especially when in the presence of governmental officials – reflects on the entire Amateur Radio Community – it is under our control as to whether the reflection is positive or negative.  They believe, to their core, that being truthful, transparent and full of good-will always prevails. They continue to support their community thru positive action, positive communication and positive energy. They are not narcissistic – but are always looking for ways to contribute, ways to help and ways to make-a-difference in other’s mission and other’s lives without going thru the evaluation of “what’s in it for us..?”.
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    My hat’s off to these guys – I share the values that they practice – they keep us all positive, and encouraged to do more in Amateur Radio. I’m a humbled that they have embraced me into their organization and look forward to working with them.
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    Bravo FPCARC – Keep up the great work. Your contributions and positive energy are noticed and appreciated..!!

A GREAT, Online Electronics Resource

Nov 21

Posted by mikelee in Antennas, Feedlines and Duplexers, ARES Training, DSTAR Projects, Test Equipment | 1 Comment

I was searching the internet last night for information regarding coaxial cables and Vp, or Velocity of Propagation – when I ran into this resource which I found to be most useful. It answered the question that I had (or at least, CONFIRMED the answer that was in my head regarding Electrical Wavelength). But then, I started browsing that same site in more detail (left navigation bar) and found it to be a treasure-trove of great information – from beginning theory, to much more advanced topics. In fact, probably not an over-statement to say that it’s the single best source of electronics information that I’ve found to date.

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I thought that I’d share so that it might benefit any of you who might be searching for similar material.
http://www.radio-electronics.com/info/antennas/coax/coax_velocity_factor.php

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Below is an excerpt of one of the pages from the site – used with full credits given.  Enjoy…

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Hint – it has to do with a Repeater Duplexer

Nov 19

Posted by mikelee in D-Star Repeaters, Test Equipment, Work Party | No Comments

Any guesses..??
Click to enlarge each of the graphs..

Repeater Coverage Plots – Coming Next Week

Aug 28

Posted by mikelee in D-Star Repeaters, Test Equipment | No Comments

As most of you know, we have always used our RF Coverage Analysis software (TAP, from Softwright) as we evaluate sites for the DStar Network and the analog repeaters. We have been users of TAP since 2002, originally  for our commercial business, then gradually introducing it into our amateur endeavors. TAP is used by many of the largest Cellphone companies, as well as by the US Government (they are the largest customer of Softwright).

We will soon be posting the coverage analysis on the NEFL DStar Blog so that all can see what both individual repeater coverages are, as well as aggregate coverage of the network. These will be PNG files (raster files), but we will also post KML files and the associated supplementary files, so that you can open Google Earth and be able to overlay the coverage on the Google Earth displays. We already have these capabilities – and have been using them for many months, but we just decided to release these to the blog.

Expect that in the next week (probably during Labor Day Weekend).

Technique – Tuning a Duplexer, On a Budget

Jul 14

Posted by mikelee in Antennas, Feedlines and Duplexers, Test Equipment | No Comments

With our advancements in the world of D-Star Hotspots (thanks LARGELY to Steve, KB4DNQ), some of you will undoubtedly be looking at creating your own hotspots – whether simplex (easiest), or full-duplex (most capable). If you ‘re thinking of full-duplex, then you’ll need a duplexer. UHF units are the cheapest, due to their small size.

Some of you have asked   “… how difficult is it to tune repeater duplexers..?” As in all things in life, the answer is “it depends”.

If you have a spectrum analyzer with a tracking generator, as well as a return loss bridge, the procedure is straightforward and takes maybe 60 minutes.

If you have just basic tools, it’s a bit more difficult and a lot less certain (you can’t SEE the results, only HEAR them). While the basic method can get you in the ballpark, it can sometimes be deceiving, in that you could be tuning into a cavity’s harmonic “sweet spot” and therefore not getting optimal results. There is no substitute for using the right tools for the job, BUT… when you don’t have (or didn’t BRING the right tools), it’s always good to be able to fall back to basics.

So here goes, using a signal generator, an attenuator, a power meter:

You can create a signal generator from an amateur radio and many feet of RG58 (which will help attenuate the signal).  Signal samplers can be had for $50 if you look on eBay, with even more elaborate units for around $100 which are laboratory qulity, more on that later.

A couple hundred feet of the worst RG-58x is about the right amount of feed line and attenuation to generate the required signal (more is better – and the lossier the better). If you need help, see the Amateur Radio Handbook for detailed instructions.

Almost all repeater duplexer are band pass, band reject. Most of the newer designs use two band pass cavities for transmit and two band pass cavities for the receiver and each cavity has a reject circuit, or notch. Each cavity should have two RF ports – if your cavities only have one RF port then you have a notch filter which is not going to get you the attenuation you need. If your cavities have two RF ports but do not have a notch adjustment then you have only a band bass cavity – you are out of luck, since there will not be enough rejection of the other side of the repeater (transmit or receive).

The signal sampler is a critical component for this procedure. RF Parts offers a very nice signal sampler, which will provide between 20-80 dB of attenuated signal. Another source is eBay – use the search term “Step Attenuator”. I got a couple of beautiful units manufactured by JFW (Model 50DR-055) which were “Factory Seconds” with only minor (almost un-noticable) cosmetic belmishes for less that $100 each. The units are rated from DC-2,200Mhz, 50-ohms, N-connectors, attenuation range from 0-30DB in 1-DB steps.  If you own or maintain a repeater system you can’t live with out one.

Tune the TRANSMITTER PASSBANDS - If the duplexer has not been tuned before for your frequency, you may want to tune each transmit band-pass cavity first, and then tune them together.

  • Connect your signal source to one side of the transmit cavity – you will be injecting TRANSMIT frequency
  • Connect your watt meter between the signal output of the band pass cavity (be sure the receiver band pass cavities are not connected) and the load (antenna or dummy load)
  • Inject a signal at the TRANSMIT frequency
  • Adjust the cavity for maximum RF power.
  • Repeat the process for each bandpass cavity
  • When all individual cavities are tuned,
  • Connect all transmit bandpass cavities together, then
  • Repeat the procedure on the cavities in SERIES and adjust for maximum RF power

Tune the RECEIVER PASSBANDS - Again, if this is the first time the duplexer is being tuned, you may want to tune each receiver band pass first, and then fine tune them together.

  • Connect your signal generator to one side of the receiver cavity – you will be injecting RECEIVE frequency.
  • Connect your signal sampler between the output of the receive cavity and the load.
  • Set the signal sampler’s attenuation to maximum (high DB),
  • Open the receiver’s squelch, and turn-up the volume.
  • Inject an on-frequency signal ample enough so it is noisy but can be heard. A 1 kHZ tone applied to the injected signal will help you hear the quality of the injected signal.
  • Now tune each receive bandpass cavity  for the clearest signal. You may have to increase the amount of attenuation on the signal sampler to keep the signal a bit noisy as you improve the bandpass tuning, doing this will allow you to hear the improvement made by your tuning adjustments.
  • When you’ve achieved the maximum signal clarity (listen for the 1khz tone quality), then
  • Proceed to tune all subsequent receive cavities
  • When all receive cavities are independently tuned,
  • Cable the duplexer for operation – cable all of the cavities, two (or three) on the receiver side and two (or three) on the transmit side.
  • Reconnect the signal generator and signal sampler – but this time for the SERIES of the receive cavities.
  • Repeat the tuning process with all of the receive cavities in series. Note that the cavities will interact with each other, so changes on one cavity will affect the signal quality coming from the other (this can be an extremely frustrating process – and is where MOST of the time is spent).

Tune the TRANSMIT NOTCH FREQUENCIES  - this eliminates your receiver signal from the transmitter input.

  • Connect your transmitter to a SEPARATE ANTENNA – not to the duplexer..!! You will be transmitting on the RECEIVE frequency.
  • Connect your receiver to the transmitter cavity where the signal generator used to be
  • Listen on the receive frequency thru the transmitter cavities (in series) and adjust the attenuation so you can hear a noisy signal. Adjust each of the transmit notches in order to REDUCE the received signal (rejecting the received frequency)

Tune the RECEIVE NOTCHES - This eliminates the transmit signal from the receive input.

  • Connect your transmitter to a SEPARATE ANTENNA – not to the duplexer..!! You will be transmitting on the TRANSMIT frequency.
  • Connect your receiver to the receiver cavity where the signal generator used to be
  • Listen on the transmit frequency thru the receiver cavities (in series) and adjust the attenuation so you can hear a noisy signal. Adjust each of the receive notches in order to REDUCE the received signal (rejecting the transmit frequency)

Always tune the notches LAST, since the notch adjustments track with the bandpass adjustments.

OK, I did just what you said to the letter and I still have a problem. Well, bummer. What are my options..?

If you still have desense in your system and the desense is constant, then find a spectrum analyzer and a signal generator and tune the duplexer by the factory procedure. There are a number of folks from Daytona thru Jacksonville who may be able to assist (cheap – for a bottle of beer..!!)

If you are using a re-purposed Commercial duplexer, you may need to change the interconnecting cables between the cavities, since each of those cables are cut-to-frequency. Although usable, it will not be optimal without exchanging. If you are using Tx/Rx Systems duplexers, we can provide you with the exact length of both VHF and UHF interconnect cables for amateur service.

Another possibility is that your duplexer does not offer the required attenuation or frequency separation needed. For a 100 watt transmitter and a receiver with a sensitivity spec of .5 uV you need about 88 dB of attenuation.

The following table lists the typical attenuation required between a transmitter and a receiver which will result in no more than a 1 db degradation of the 12 db SINAD sensitivity. This information is based on a receiver with .5uv sensitivity (which is pretty crappy).

Transmit Power 2 Meter
600 kHz. Frequency Separation		 70 CM
5 MHz Frequency Separation
25 Watts 82db 55db
50 Watts 85db 58db
100 Watts 88db 61db
250 Watts 92db 65db
350 Watts 98db 70db

The IFR-500 Service Monitor

Jul 2

Posted by mikelee in D-Star Repeaters, Test Equipment | No Comments

While we are huge D-Star proponents, we also use and maintain “old” analog repeaters as well. Test equipment for maintaining analog radios and repeaters is quite different from the digital world.

We’ve been using a series of Service Monitors from IFR Systems (now Aeroflex) for the last 18+ years. Our primary field Service Monitors are a pair of  IFR-500′s – a compact (albeit HEAVY), full function service monitor which tests to 1Ghz and is able to operate for short periods of time on internal battery power. The IFR-500, like all reputable devices, tests for the following major parameters:

  • Receiver Sensitivity
  • Receiver Signal to Noise Ratio
  • Receiver Tone Signaling (TSQ,DCS, 2-tone, etc.)
  • Transmitter Power Output
  • Transmitter Deviation
  • Transmitter Frequency Error
  • Testing in AM/SSB/FM-Narrow, Medium and Wide Mode

Following are the manufacturer specifications on this device.

(click to enlarge)

The FSH313 Spectrum Analyzer

Jul 1

Posted by mikelee in D-Star Repeaters, Test Equipment | No Comments

We use a number of instruments for various aspects of installation and maintenance of the repeater equipment. In a previous article, we reviewed the Agilent N9330N Cable/Antenna Analyzer – a marvelous piece of equipment to test for faults in transmission systems. We use that instrument routinely – including just this week to diagnose cable and antenna problems at the Flagler EOC due to a lightning strike.

Today, we’ll give you more information about the Rohde Schwarz FSH3-13 Spectrum Analyzer that we use for tuning of duplexers and analysis of active devices like receiver pre-amps. We’ve had this instrument for about 6+ years now and it has been marvelous. Sweeping to 3Ghz, with a built-in Tracking Generator (for performing frequency response testing), as well as an integral Return Loss Bridge, Vector Analysis and Distance-to-Fault software, the FSH313 is usually part of our standard “Kit” of test equipment when going to repeater sites (along with a the IFR-500 Service Monitor and the Agilent N9330B). Key aspects of the FSH3-13:

  • Hand-held – less than 6 pounds
  • Daylight-bright screen
  • Sweeps to 3Ghz with1Khz resolution across the entire sweep range
  • Built-in Tracking Generator, sweeping to 3Ghz
  • Distance-to-Fault, being able to scan cables for kinks, shorts and opens
  • Offline software analysis of captured results

It’s expensive, as illustrated on the price list. But precision is never cheap. Consider the task of tuning a duplexer – you can do it with 2 Handheld radios, by ear along with a VSWR meter – and probably come close. But it is hard to “see” the frequency response of the duplexer cavities without a function like a Tracking Generator. In short, it’s crude and not time efficient – and you don’t see the whole “picture” of frequency response. What should be a 45 minute job with an FSH with ABSOLUTE CERTAINTY, may be a 3-4 hour task with no certainty using the wrong tools. Is it expensive..? – absolutely, but the time savings and certainty are PRICELESS.

Following is information from Rohde Schwarz and from Test Equity – one of the distributors of precision test equipment whom I deal with on a regular basis.

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