Software Defined VHF / UHF

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K6BBC, Sep 4, 2014.

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  1. K6BBC

    K6BBC Senior Moderator Volunteer Moderator Platinum Subscriber QRZ Page

    I'm becoming interest in the SDRs and don't seen to find any transceivers for VHF/UHF. I would think this would be a natural. Does anyone know if they exist yet?

  2. W6RZ

    W6RZ Premium Subscriber QRZ Page

    Here's something.

    If you're serious about SDR, there are fairly low cost transmit capable boards available.

    bladeRF (300 MHz to 3.8 GHz)

    hackRF (10 MHz to 6 GHz)

    Ettus B200 (70 MHz to 6 GHz)

    Be aware that these devices aren't exactly plug and play. They're more geared towards experimentation, Linux and GnuRadio. For example, I'm using the bladeRF as an amateur digital television exciter.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I can't think of any advantages to SDR for VHF-UHF other than perhaps a whizbang GUI. In terms of "performance," on VHF that's all in the first couple of stages (RF amp, first mixer, and filtering for those) and everything after that doesn't matter so much.

    SDRs mostly convert from RF directly to audio, and on HF that could have some advantages (fewer mixing products and stuff). On VHF...not so much. Signals on VHF are weaker, and the "juicy" ones we really want to work are often just over or in the noise.
  4. N9DG

    N9DG Ham Member QRZ Page

    For me applying SDRs to 50, 144, 222, and 432 has been a huge boon. After running them for almost a year and a half now I will never go back knobs and buttons to find and tune in signals. And I have top notch receiver performance as well. As of today the best performing, and most capable spectrum display SDR approach to V/UHF on 144MHz and up is via transverters.

    With a GOOD panadapter / waterfall you will see signals that you would not likely have ever found by slowly tuning across the bands. "Slow tuning" is a truly horrible way to find weak signals on any band, especially so on VHF and above where they tend to be farther apart. Perhaps even worse is just sitting on the calling frequencies.

    This presentation by Roger, W3SZ should be required reading for anyone who thinks they want to get serious about V/UHF weak signal work. The first 9 pages explain why it is desirable to do so. The pages after that go into detail of Roger's actual implementation.

    You certainly don't need to get as elaborate, or as complicated as he did, but getting some good displays on the 50 and 144 MHz bands is well worth the effort. And I have found it to be worthwhile thing to do on 222 and 432 as well. I have built something that does most of what Roger's system does, and did so with all off the shelf hardware, and no custom built hardware or software at all. So in my case it was almost exclusively an exercise in systems integration. With my configuration I have the ability to listen to multiple receivers per band simultaneously, and watch all of them at the same time as well. All of which is what I specifically wanted to be able to do at the outset. Providing for that greatly simplified the station hardware and software setup, and also allowed me to skip all of the mic, PTT, and speaker switching that Roger did. But he specifically wanted to only listen to one receiver or band at a time, while still watching the others.

    It also important to not only do this on just one band at a time, but several at the same time as Roger's presentation talks about. You really don't know how much stuff you are missing on the “other bands” when you are running a signal band at a time bandswitched configuration, i.e. anything out of JA land that is commonly referred to as a “DC-daylight” radio. Once you have the ability to watch multiple bands you will see, and then get a chance to work signals that the one band at a time operator will never even know existed. You will feel totally blind without it after running with it for awhile. So it's not really just about “you can't work what you can't hear” on 50 Mhz and up it is actually more about “you can't hear what you don't even know is there”. The DX spotting clusters are woefully inadequate for alerting you to what's on the bands as well, so you really do need to have you own equipment to make that possible for you..

    There are several approaches to apply SDR technology to V/UHF weaksignal work. Some are better and easier than others. One approach is to try and add things the RTL dongles or low cost I/Q mixer designs to existing radios. Takes considerable fiddling and experimentation to make it all work. And in the end gets to be rather kludgey. In the case of the 8 bit sampling RTL dongles you will likely run out of dynamic range, 8 bits just isn't enough. Though I've seen reports of people making good use of them for 50MHz and up operation. And I suspect that they beat most, if not all, in-radio scopes for display quality.

    You could also go a QRP SDR radio driving transverters route with something like the Flex-1500. But it too has capability and performance limitations. One unacceptable limitation for me was the max of only 48 kHz of displayed spectrum of the Flex-1500. I consider a 192 kHz wide display to be a minimum.

    What I ended up with is a mix of some OpenHPSDR Hermes DDC/DUC low level transceivers boards, and a Mercury/Penelope board set (electrically and functionally the same as a Hermes for all practical purposes), and also a Flex-5000 that I already had in the shack. All of the SDRs are used as IFs for my DEMI transverters driving 100-160W bricks depending on band.

    To build a similar configuration to mine today by buying all new hardware (Hermes/DEMI/brick amplifiers) will run about $2K per band. Not cheap, but provides a lot of capability. I had most of the RF gear on hand going back 10-25 years now. So it was mainly a matter of adding the SDR parts to make it all play. I hedged my bets 10-15 years ago that SDRs would get to where they are today, so I went the transverter route instead of DC-dayight or other knobbed multi-mode models back then in anticipation of SDRs getting to the performance and capability level of the Hermes today. I made a good bet back then.

    I also from the outset knew that I wanted multiple simultaneous receivers and visual displays on the 50, 144, 222, and 432 MHz bands. To try to get that with dedicated DC-daylight and/or traditional multi-modes per band would have cost nearly as much, and still wouldn't have any scopes, or second receivers per band. So in the end the Hermes driving transverters is actually one of the more economical ways to build a V/UHF station once you've committed yourself to having simultaneous band coverage with both multiple receivers and good panadapter / waterfall displays. They'd even be cost competitive approach in a band switched configuration by switching transverter IF lines. I know of folks who are doing that as well.

    The Cross Country Wireless Sentry mentioned in an earlier post is certainly one to watch. It is definitely heading in the right direction for properly applying SDR to V/UHF weaksignal work. Now will need to wait and see just how well it truly works in practice.

    As for the bladeRF, hackRF, or Ettus approaches, you will be in the wilderness all alone figuring it out for analog CW/SSB/WSJT, i.e. “traditional” weak signal operating. Those are all geared towards digital high data rate modes (think wireless networking etc.) and experimentation vs. putting something together to use day in and day out.

    So there are a number of choices, though not much in the way of super simple "open the box, hook up a few cables and run".... Yet..... But it is not really any more difficult than running transverters has always been. To me that extra effort up front setting up transverters along with SDRs is completely worth the effort.
    Last edited: Sep 5, 2014
  5. AA9G

    AA9G Ham Member QRZ Page

    Think harder. Better yet, buy one and play with it. Your'e Helen Keller and the rest of the SDR crowd is trying to explain a rainbow to you. :)

    Duane, great post, that link is awesome for me because I am planning (hoping) to use this ANAN 100d of mine for weak sig VHF too.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I've been doing "weak signal" VHF-UHF (and SHF) work for over 40 years, have won many VHF-UHF contests (including #1 nationally), authored the CQ "VHF" column for five years...and owned a Flex SDR1000A when it first came out, so I was a pretty early adopter of SDRs (also had a Flex 5000 for about six months).

    For digi mode work, this could be useful; however all my weak signal work is CW and SSB, and very little digital. I had a 70cm e.m.e. station for years (1 kW output to eight stacked K2RIW Yagis) and made hundreds of e.m.e. contacts before any WSJT modes were invented, so they were all CW. That was fun and challenging, since if you couldn't actually "hear" the signal, there was no way to work it.:eek: I got spoiled by that.

    But having to sweep 192 kHz is useful for VHF-UHF-SHF WS work? How is it useful? For digi e.m.e./m.s. stuff, everyone knows exactly what frequencies to use and the majority of contacts are pre-scheduled for exactly one frequency. For CW, there's a very small slot on each band where everybody is. On 6m, it's 50.080 to 50.100 -- 20 kHz. On the higher bands, it's even narrower. The only time stations spread out above about 50.140 on 6m SSB is when the band is open and during contest weekends when you don't need to "spot" a signal on a screen, they're all over the place. On bands like 3cm, everybody's on 10.368.1 and almost nobody deviates from that frequency...certainly not by 192 kHz, or usually not even by 19.2 kHz. And so forth. On the SHF bands it's easy for 50 stations to all share exactly the same frequency (and they usually do) because the antennas are so sharp unless two stations are aimed directly at each other, there's no signal.:p

    I won the ARRL UHF Contest nationally three years ago (single op, highest score) using a microphone and a keyer and a bunch of transverters. I do believe if I had an SDR with a 192 kHz spectrum display, my score would not have increased by one point.

    Of course, that's just my opinion. If yours is different, tell me how it would have improved using an SDR. I'm happy to listen.
  7. N9DG

    N9DG Ham Member QRZ Page

    I find it extremely useful. For example during FD 2013 I was on 2M handing out some Qs on the weak signal part of the band. As I'm making Qs nearer 144.200 I see a SSB signal pop up on 144.125. So I park my second RX on that frequency and find that it is a fellow who decided to give 2M SSB a shot and had mistakenly thought that 144.125 was the 2M calling frequency for SSB work. If I had not found him, he may have very well gave up on 2M SSB and never worked anyone.

    And a recent VHF contest I again spotted a signal down around the 144.125 area and worked him for a Q and mult. This was a station who DID NOT ever show up on a frequency closer to 144.200.

    And in most VHF contests I will find and work a few stations on 222 or 432 first (or only), simply because I saw their signal pop up on the display on a frequency that is some distance away from the .100 calling frequencies for those bands.

    In this area rovers spread out on frequencies like 144.230, 235, 240, 245, 250 etc. - or frequencies below 144.200 by about that same amount. Those are the frequencies they each use as their primary operating frequencies. And they spend very little time on, or closer to 144.200. They typically only drop to 144.200 when they have finished working everyone on their primary frequency. The trick to work rovers far away and weak is to get to them before the crowds do. So being able to see them when they first pop up in a new grid is a big benefit. So if you are never straying more than +/- 20 kHz of the calling frequencies then you are missing things, you just don't know it..

    And I will see and work signals on 6M much above 50.150 even when the band is not wide open. I know of a station in the rocky mountain states who parks most of the time 50.190. In many cases he will not ever show up on 50.125.

    And during nice 6M openings I can be working the stuff well above 50.150 and then see something appear in the DX window, jump on it, work it, and go back to the frequency higher up the band. Without a good display it is highly likely that I will have never even known that the DX station was even there at all because the conditions that made them workable was very short lived.

    And keep in mind watching the 192 kHz spectrum is what you do while CQ'ing on a chosen frequency. So basically as you un-key after your CQ, you watch the rest of the band that you are CQ'in on while listening for a response and/or you tune the second RX on that same band to something new that you may see come up on the display. And if you get no response to your CQ, but find someone new elsewhere you flip to that frequency to TX, make to Q, flip back and then resume CQ'ing with very little disruption to the rhythm of your CQ'ing. That example was just on a single band, now image doing that same thing across 4 or more bands at the same time. And even better, to be actually watching and tunning around for signals on those other bands while you are transmitting on another. Again if you spot something on another band, jump there quick and work it. And again do so with little disruption to your CQ run frequency. None of the 'no spectrum display, single band at time' radios like the 'all bands in one box' radios all are, will allow you to do that.

    I've been the VHF+ weak signal game for about 30 years now. And the PC-based SDR stuff with their truly good spectrum displays is actually a long time dream of mine that has finally come true. Early on I recognized that VHF weak signal work is all about having the ability to know what is going on across a lot of frequencies all at the SAME time, and ALL of the time. And to then a
    Last edited: Sep 6, 2014
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    N9DG: Nice story!

    Here, the rovers publish their intercom frequencies so everyone knows exactly where to look for them; the Southern California Contest Club, for example, is the largest rover group (formed many years ago by N6NB) and only uses 223.42 as liaison/intercom among themselves, so everyone knows that's a "go to" frequency. Then they work each other on 50-144-432-902-1296-2304-3.4G-5.7G-10.3G using that same frequency just changing the MHz digits, so everyone knows to look there also -- not much exploration involved and they announce far and wide every time any of the group (or all of them) cross into a new grid and park to operate.

    Around here, 144.200 is commonly used by contesters but they just call there and then announce where they'll be listening. "WB2WIK calling CQ contest and listing 144.250" or something like that. So for "listening," it really pays to listen on 144.200 -- a lot. Ditto the other bands, with 222.100, 432.100, 902.100, 1296.100, etc.

    Things vary by region a bit, but here this is the common way to work VHF-UHF contests and it's also the way to win them.

    In 2010, in the August UHF Contest, I had the highest score in the country and just wanted to see if that could even be done from the west coast, as nobody ever did that before; the traditional national winners were in the northeast or the midwest. I was also the QSO total winner on seven out of the eight bands operated (missed it on 432 MHz! -- got it on the other seven, 222 through 10,368 MHz). Used single HF rig and transverters, with the transverters remotely installed over the top of a 70' tower at about the 80' level, with very short feedlines to all the antennas (maybe ten feet long on 222-432 MHz, but shorter than that on the higher bands, and only about 36" long on 5.7 and 10.3 GHz), all installed at N6NB's home in Orange County (no hilltop, it's actually only about 170' above sea level, but a good shot up and down the coast with no obstructions to the ocean).

    I was the only operator and the only one there, as Wayne was out roving, himself. Kept a manual log (no computer) and when converting that to a computer log the week after the contest, found exactly one dupe out of over 500 contacts. Not so bad. And manual logging is easier on my eyes as I don't have to stare at a screen.:eek:

    Also operate a mid-sized M/M VHF-UHF contest station, N6VI atop Frazier Peak, with about six other guys for the June contest 2011-2013 (didn't do it this year). In 2013 we placed #1 west of the Rockies, and #5 nationally in the M/M SDRs, no band scopes, nothing like that. Just rigs with mikes and key paddles, from a good location (8013' asl overlooking L.A. and the Central Valley) using good antennas on towers which we unfortunately have to erect and also dismantle, as nothing can be left up there. We keep very busy and beat everybody anyway, and don't tune around much; mostly sit on one frequency and call CQ, and log answers; on the higher (microwave) bands, most contacts are "by sked," with the skeds made on one of the lower frequencies like 144 or 432 MHz, and we just use 1.2 GHz FM handhelds as an intercom.

    Different strokes, for sure.:eek:
  9. N9DG

    N9DG Ham Member QRZ Page

    Not sure what happened to my previous post, but it got truncated a bit... The rest of what I was saying was:

    "…. And to then also have the ability to get to what you do see very quickly. PC-based SDRs are the enabling technology to make that possible today, and to do so a fairly reasonable price. And I've also observed that all of the Internet based spotting networks and other propagation indication / predicting sites fall pretty short of allowing you to know what is really going on. They simply fail to show you what is all actually happening. I have found and worked stuff that those sites either didn't ever know about, or had not predicted should have been possible. So they are simply not a substitute for a BETTER RADIO like SDRs can be when done properly. However of course the operator using them does have to actually know how to best use it. I can assure you though that applying traditional knobs and buttons thinking and operating style to them will leave more than half of their potential unrealized."

    Some additional thoughts:
    I have been doing 100% computer contest logging since 1988, would never do paper again for that either. In the recent contests I have gotten my logs wrapped up and submitted to the contest sponsor in less than 30 minutes after the contest ended. And as part of that to have also imported all those contest log entries into my master logbook as well.

    When I work with the SDR display screens I don't even see the screen itself, I see past them, what I only really see is just the graphical representations of the real-time RF that they present. In the past I would always be creating in my mind's eye "pictures" similar to that as means to catalog and keep track of who was where, when. Now I let my SDR radios do the graphical part of that for me :).

    For grins I compared my numbers for June 2013 ARRL for the bands I share in common with the N6VI multi op and see that just me, myself, and I running SOLP had worked more multipliers on 144, 222, and 432 than the N6VI multi-op did. I couldn't match the Q counts being further away from any big population centers. And though I do have grids a full 360 around me, there are a lot of them in my northern direction that have no contest activity at all, so is close to being the same as being an ocean. And most of my Qs were SSB/CW only in the weak signal parts of the bands, and most of the rather few FM Qs that I made were on 222. I had made no precontest skeds, or made any WSJT Qs either.

    N6VI: 50MHz:445/110; 144MHz:227/17; 222MHz:130/16; 432MHz:129/14
    N9DG: 50MHz:157/77; 144MHz:96/28; 222MHz:36/19; 432MHz:56/22

    I atribute much of my success to the equipment, though my location is certainly a good location, and the antennas are very good as well.
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Good deal, and good results.

    Try from California sometime, it's a really different world. Grids are grids but problem we have out west is there are many grids that do not have a single active VHF SSB-CW station in them, and for that matter grids that have almost nobody at all in them. Rovers try to hit those if they can, but it's a long drive across deserts and over mountains (which is pretty much why nobody lives there). To work more than about 17 grids from here requires scatter or Es; even a tropo duct won't really help because the mountains break those up (we're talking 10,000' mountains and higher, and the ducts don't go over them).

    As an example, within just a few hundred miles of me are DM02 (zero human population), CM93 (ditto), CM86 (ditto), DM17, DM24 and DM25. Those last three have some human population but are over very big mountains then across very wide deserts and no active weak signal VHF ops; if a "rover" goes there, he'd better have high power and big antennas because low power and small antennas won't make it back here. The other problem we have is there are some great VHF-UHF mountaintop locations that would be perfect for contesting, but there's no way to get to them. There aren't any paved roads, and in many cases aren't even any unpaved roads...just hiking trails and they can be pretty primitive. Not good enough to carry a station that could work multiple bands with any effectiveness.

    Most of our mountaintops (hundreds of them!) are in protected state or national forest lands. Even Mt. Baldy, at 10K feet overlooking all of L.A. (the snowcapped peak you see in the background of "downtown L.A." postcards) has no sort of road to the summit. One could hike it and maybe do a single-band operation with a very small yagi and a battery...but no real serious effort could be done (everyone's tried).

    We are fortunate at N6VI to get to operate from Frazier Peak, which is about 75 miles northwest of L.A., because it's in a national forest and the summit is not open quite a lot; and when it is open, there's no "overnight camping" allowed without a very special permit that's not easy to get. Marty N6VI has successfully achieved the permit but it takes some politics.

    And even reaching the summit by motor vehicle is not for the feint of heart. It's 6.5 miles up a dirt and rock "road" (unpaved) that has about a 4000 foot vertical and dozens of sharp switcbacks right on the edges of cliffs that have a 1000' dropoff and zero guard rails. I've done that at night several times and if I have a passenger who doesn't know the area, they're usually screaming and then at the bottom want to get out and throw up.:p

    These issues aren't just with California: Nevada, Utah, Idaho and lots of places "out west" really have the same issues.

    If you want some real fun, travel west and try one from out this way.:eek:
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