[NLRS] 2m-440 Rigs

[Dr. Gerald N. Johnson]

I found about 48 years ago that it is practical to improve the strong 
signal handling without hurting weak signal copying by proper gain 
distribution in the preamp, converter, IF situation. The process 
requires making system NF measurements, not just of the components, and 
the narrow bandwidth of the IF receiver prevents using most automated NF 
meters. That is the basis of my paper first published in the K2UYH 
newsletter July 2011, CSVHF 2012, and on line at 
www.geraldj.networkiowa.com/papers/2012/Intermod2.pdf
Its not necessary for the noise source to be calibrated, just with a
stable amplitude, and my paper
www.geraldj.networkiowa.com/papers/2012/predictablenoiseA.pdf
published last year at CSVHF and MUD shows one handy noise source.
Basically, every dB of front end gain that can be removed without 
affecting the system NF is a dB strong signal that can be handled. The 
common ham criteria of the preamp giving at least a 10 dB noise rise is 
too much front end gain.

Jon, I think you meant "bank" account rather than "band" account though 
band account fits the topic. :<)

While the 897 and 857 seem so share some accessories, like TCXO, 
mechancial filters, and maybe the originally optional DSP and function 
almost exactly the same, I think the main boards are not 
interchangeable. Some of the front panel parts don't interchange, the 
857 has a removable front panel for remote location that the 897 does 
not. The 897 head phone jack is 1/4" while its 3.2mm in the 857.

Reports are that the 857 and 897 don't have the dynamic range of the IC 
756 PRO, but so far hear near the Boondocks, I'm happy with my 857s. And 
I've not been pleased with 746 or 756 Icoms at Field Days.

I have a TR-751A apart on the bench, been apart since October. Bad 
volume control, RF gain control, RIT control, and inconsistent main 
tuning encoder. I've soaked the volume control and got it partly 
working, though the radio works better with the top part of the control 
shunted with a 10K resistor. And the RF gain is maximum when that open 
control is shunted with a 10K resistor. No control but I've not used RF 
gain controls much and this might be an IF for 10 and 24 GHz. Some 
inexpensive lower resolution encoders that may work for the tuning dial 
arrived today.

If that encoder isn't satisfactory, I may be looking for another 857 or 
817 for the second 10/24GHz station.

One nice thing I like about the 857 is that it allows running CW which 
the mode is set for SSB by simply closing the key. Requires setting BK 
on from one of the front panel menu entries. There is that BK option for 
CW break in operating according to the 817 manual, does it allow such 
mixing of modes?

Jon, where did you find replacement controls for your 751?

73, Jerry, K0CQ



On 3/25/2013 8:11 AM, w0zq at aol.com wrote:
>
>
>
> Hi Kirk -
>
> This is a complex question that entails a lot of variables ... how you prioritize all those variables leads you to different answers.   For example, are you an appliance operator or do you like to dive in to work on interfaces and even customize software?  Roving, fixed, or both?  What bands?   Is FM important to you?  Contesting?   How big is your band account.   Etc, etc.
>
> For me, I like to contest so I need to be able to listen on three bands at one time; 6m, 2m and the microwave band (ie, 902, 1296, etc).   Bill, AWU, and others, have had good success using SDR-like radios so that they can not only listen on multiple bands simultaneously, they can "watch" them as well.  The SDR formats work well for this, much better than the older technology that is on the HF radios like the Icom Pro III's (which work very well on 6m).  So however you do it, you need to be able to listen on 6, 2, and your uW IF rig all at the same time.
>
> Regarding radio performance, lots to consider.   Here in the big city we are close to lots and lots and lots of RF signal source including other in band VHF ops.   Dynamic range and strong signal handling capability is important.  We cannot use RF gain and preamps as easily as those who live out in the sticks.  Most 6&  2m preamps are fairly wideband and those out of band, but adjacent, signals can be a problem on 6&  2m.   Aiming your antenna up (EME) can help some, but for terrestrial, it is what it is.
>
> For 6 and 2m, from a performance perspective (ie, a blend of sensitivity, dynamic range, and selectivity), it will be hard to beat a quality transverter feeding a quality HF rig.   This was true years ago and its still true today.  Obviously some station integration is needed if you are going to use a transverter and its harder to take roving!   Check out the DownEast catalog at http://www.downeastmicrowave.com/cat-frame.htm&  click on the 2m transverters and read up on their design and how their receive side is designed to address these issue.  Then, after transverter design discussons, the next discussion usually turns to what is the best IF (HF) rig to work with such a transverter.  There you will have the same topics/discussion as the HF guys have regarding the best noise blanker, operator controls, etc, etc.   Dynamic range for the IF rig is important too .... you don't want to spend money on a high performance transverter only to feed it into a crummy HF rig.
>
> If you are willing to trade off some performance for convenience, its hard to beat the TS2000, FT897, etc, etc, style radios.  My experience is that where these radios tend to fail is in dynamic range and with birdies .... usually sensitivity is not an issue.  I suspect that both are due in large part to what also makes them such a marvalous rig ... they lack selectivity being more of an open receiver front end.   However, if you live out in the sticks with a low RF environment, you may find that these radios work just as well as the transverter route discussed above.  Note that the FT857 and FT897 are exactly the same radio with different external wrappings.  These are marvelous radios, often 160m through 440, that provide good performance in a plug and play way.  Currently my home station for 2, 222, and 432 is a FT897 that also forms the basis of my VHF+ rover station ... I use it both fixed and when roving.  That said, be aware that I am not active on EME or digital mo
des
>    right now .... if I was I would be in the market for a good 2m transverter to feed my Pro III.
>
> For 902 and up, I use an old 2m monoband rig, the TR751A.  This also goes with me when roving.  Some have been using SDR IF rigs to help them find the other stations as frequency stability is sometimes an issue along with sharp beams and weak signals.
>
> So in summary, if you are looking for top performance for a fixed station, its hard to beat a transverter into a good IF rig.  That IF rig could be an SDR, or a top grade HF rig.   It depends on how much work you want to do on station/system integration; maybe both hardware and software.   For contesting, you need to be able to listen on 6 and 2m at the same time ... that means two radios.  If you run any of the uW bands, that means three, albeit you could use whatever your 6m rig is as a switchable IF on the uW bands too if you are willing to be off of 6m when your running uWs.
>
> Hope this helps !
>
> 73, Jon
> W0ZQ
>
>