TS850 .v. 870 and them pesky Loran lines...
I've been playing (that's a good word for it more than "research") on
comparisons between the TS870S and the TS850 at this location - the major
(major) Noise source is QRN from storms this time of year, as the SMPU's
etc level is pretty low.
I don't have to worry about Imod/xmod here/selectivity issues here and I
run the RX on SSB at b/ws of around 2.8Khz so I can capture DCF39 and 137Khz
at the same time on 2 or more Argo sessions.
With the agc "on" both receivers the noise levels (crack bang whallop) sits,
at say S9+10. The 850 is a more sensitive down here at LF but the noise
figure differences is blown away by the QRN, well at this time of year
anyway, on these larger rx arrays in use here.
With the AGC's both Off on both receivers the 870 is able to delve into the
noise and return better s/n. or Argo decodes at dot 30 - its not a small
difference, its Huge.
It seems to just be the NB on the 870 is better at blanking out lightning
and maybe the AGC constants even with off are still "on" on the 850?
For sure, without the NB on and the AGC ON I can hardly see a signal that
is 30dB above noiz between these near constant crashes.
Given the tests so far running both receivers from the same source and not
equalizing levels for the 850's better sensitivity, the 870 is able to "see"
into the noiz more effectively than the 850 (with either NB1 or NB2 or
combinations of both on the 850) I think I've also eliminated the levels/
AGC nature of the Argo plots as a possibility too....
On a typical noisy day here in Okie - and remember these results are for
this type of noise only...
using Argo the 870 gives some 15"db" results than the 850.
This would explain the very good results, much better than anticipated
results in Ghana and Costa Rica - Even though the noize level was painfully
high the 870 produced DCF39 at good levels.
Another anomaly -
I have another brain scratcher which I haven't yet figured out and may be a
"high angle" reception issue (or not), but my large 350ft circum tuned loop
(NE/SW firing) produces good daytime Loran lines from stations in the Gt
Lakes area and Southern US chains (hundreds of miles away)- but the smaller
K9AY which can put a heart shaped back lobe in 4 directions does not. At
the moment we lose the Loran lines for most of the night....
But the K9AY does the business and actually produces better s/n from Eric
XFX down the road (most ground wave during the day but definately
skyway/groundwave mix during the night and a dawn/up to 3 hours after dawn
enhancement of about 4dB over average...)-
I switched the K9AY to fire other directions, but no it still doesn't
produce strong Loran lines. I've checked to see if the Loran lines are
something else ie Imod or some other nasty in the rx chain but No.
The K9AY is shown to have a take off angle of 25 deg (hmm) but the
difference is so manifest - its will be interesting to compare tonight when
DCF39 comes in and or we start to see longer haul inter US 137Khz activity
and see whether seeing Loran lines or not means seeing long(er) haul
signals.... any thoughts on this?
Laurence KL1x/5 still in Oklahoma
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