>-----Original Message-----
>From: Dave Bowker <dbowker@shire.sjv.net>
>
>>Hi Jim,
>>
>>After following this thread, I have to question the instrumentation and
>>methodology used to obtain the data. Looking at the specs for Times
>>Microwave LMR-400, the loss per 220 feet should be as follows, neglecting
>>connector loss.
>>
>>Freq.... Times Specs... Your Measurements... TwinLead
>>=================================================
>> 7.050 0.7 dB..............1.8 dB............................0.4 dB
>>10.109 0.9 dB.............. 1.9 dB........................... 0.5 dB
>>14.020 1.0 dB.............. 2.1 dB........................... 1.0 dB
>>21.021 1.25 dB............. 2.7 dB........................... 1.6 dB
>>
>>There appears to be an unexplained delta of approx. 1.1 dB, (except at
>>21.021 where it is approx. 1.5 dB) between what should be expected per the
>>Times Specs and your measurements. This "delta" does not appear in your
>>measurements of the TwinLead line, assuming the all the same components
are
>>involved in the measurements, except for the 20' difference in length.
>
>Hi Dave,
>
>All the same components plus, a kW Johnson Matchbox and an
>Amidon balun with losses are added to the system and included
>in the twinlead loss data, along with the same coax switches and jumper
>cables/connectors as measured along with the LMR400, as detailed in
>my original posts. These switches, jumpers, and connectors were included
>and mentioned in my original post.
>
>Yes, I agree something is/was wrong! It is, in part, other transmission
>system components, as mentioned above; but also, still, more loss in the
>LMR than the specs would say, see on below.
>
>I get exactly the same Times spec numbers you list for my run of LMR400
>when I use the Times Microwave calculator at,
>
> http://www.timesmicrowave.com/cgi-bin/calculate .
>
>So I can confirm also the Times spec on their coax.
>
>However, I measured this excessive loss two ways, neither was lab
>quality, however, hi. First, I used the new MFJ259B set which
>has a cable loss mode; next, I used a Bird 43 watt meter, simply
>measuring the power out of the rig and out of the coax at the far end. I
>figured the absolute power accuracy of the Bird wasn't important,
>as it was just the delta in which I was interested.
>
>Then I realized that I had been including losses in several coax switches
>here in the shack, as well as a large number of PL259/SO259 pairs on
>jumper cables among the coax switches in my loss measurments. So,
>I eliminated all these, and re-took the data. This time my LMR400
>data read as follows:
>
>7.050.....1.0 dB loss in 220 feet of LMR400
>
>10.109...1.2 dB
>
>14.020....1.3 dB
>
>21.021....1.8 dB.
>
>So there seems to still be at least 0.3 dB of excessive loss in my
>particular piece of LMR400 with it's connectors on each end.
>Now, .3 dB does not sound as if it is much, but it is greater
>than the transmission line spec difference/100ft between LMR400
>and 9913, for example! And .3 dB delta must be important
>enough to have some guys pay more than double the LMR400
>price for LMR600 which is spec'd by Times as only about
>0.2 dB less lossy than LMR400.
>
>All in all, I am very pleased with the results of my switch to
>"450" ohm, #14 gage wire, twin line! With it, and all my
>switches and jumpers, I am equalling/bettering the bare spec
>performance of LMR400 all the way through 20 meters, and not
>much worse at 15 meters.
>
>Put me down as a very satisfied user of thin line at HF.
>
>73, Jim, KH7M
>
>Oops, I neglected Dave's on going comments, see below:
>
>>Are the losses being measured "true" losses or is there some other
>>mechanism causing this error in the data?
>
>
>Probably my inept handling of the LMR when I installed it; I mangaed
>to get it "kinked" a couple of times; it was very tough to "unwind" from
>its coiled rest position and string it out to my antenna field!
>
>>I question this because I have had extensive experience with LMR-400 in
>>both commercial and amateur applications and the losses per 220 feet at
the
>>frequencies you took data appear to be considerably excessive based upon
>>laboratory measurements I have made (using precision lab equipment with
>>calibrations traceable to NIST).
>>
>>73, Dave, K1FK
>>Fort Kent, ME
>
>
>Obviously I was not using lab gear, hi.
>
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