[TowerTalk] Bird 43 and Coax Set up/LMR losses

[Jim Reid]

Hi to all interested,

I rcv'd a great suggestion from Stephen, K0SD, this morning,
so I have followed it;  see below.

Stephen wrote:
>Jim,
>   Do you have a good wattmeter?  If you have a Bird 43, or something
>similar, use it and read the power at each end of the 220 ft line.  Say,
>100 w in, and ??? out on 15 meters.   If you have 1.6 db loss, it will be
>evident on the watt meter.   You might let us know what you do find.
>
>Stephen Budensiek, K0SD in NC

My earlier attempts, also added stuff posted since Friday on shack
gadget losses as well as LMR400 transmission line losses.

>On Fri, 26 Jun 1998 11:25:17 -0900 Jim Reid <jreid@aloha.net> writes:
>>Also,  using the 259B to measure the loss of my length of 220 feet of
>>LMR-400,  I measured the following:
>>
>>1.830.....0.5 dB, or about 0.23 dB per 100 feet.  LMR400 should 
>>                                   be about 0.14 dB at 1.8mHz
>>
>>3.520.....0.7 dB,  or 0.32 per hundred,  should be 0.2,
>>
>>7.020.....1.0 dB,  or 0,45 per hundred, should be 0.29,
>>
>>21.020...1.6 dB,  or 0.73 per hundred,  should be 0.5.

Within an hour of getting K0SD's suggestion,  I had borrowed
John's, KH6FMT, Bird 43, S/N 15794 (it looks pretty old and
well used,  hi).  He had both 1kW and 100 watt 2-30 slugs,
so took both, but for this used only the 100 watt insert.

Essentially,  repeated everything reported yesterday when was
using the MFJ-259B,  and essentially every test measurements
were nearly the same with the Bird as with the MFJ.

I set the Bird so that it read exactly 100 watts forward,  and noted
any reflected power and vswr;  also recorded what was read on
the P-3000 meter at the same time,  true forward,  reflected and
vswr.  These readings were used to re-establish same conditions
out of the xcvr when the Bird was moved about and out to the
Top-Ten switch at the antennas.

Without listing all the data measured,  these are the results:
Used frequencies on 40 and 20 where yesterday's tests had
shown 1.0:1 vswr and X=0 on the MFJ259B.  

Note:  About 15 meter  measurement/data.

Had to fiddle around with the data and account for a
1.5:1 vswr,  lowest achievable on 15 (100 watts out of xcvr,
resulted in 6.5 watts  reflected per the Bird,  but only 3 watts
reflected per the P-3000 where the 1.5 vswr was read).  So
I used 93.5 watts watts forward as Bird measured when
compared with the only 50 watts read on the Bird out at
the Top-Ten switch coming out the end of the long LMR-400
line.

40 Meters

f=7014,   loss of entire chain,  xcvr, in shack switches, LPF, linear,
                   and 220 feet of LMR-400 measures to be 1.8 dB!!

 	Loss of in shack stuff alone,  0.76 dB
	Loss of 220 feet of LMR-400,  1.04 dB,  or 0.47 dB/100 feet.

20 Meters

f=14004,   loss of entire chain, xcvr to TT switch input terminal,  2.1 dB

	Loss of in shack stuff,  0.66 dB
	Loss of LMR-400 line,  1.44 dB,  or  0.65  dB/100 feet.

15 Meters

f=21058,    loss of entire chain,  xcvr to TT switch input,  2.7 dB.

	Loss of in shack stuff,  1.2 dB
 	Loss of LMR-400 line,   1.5 dB,  or 0.7 dB/100 feet.
                   

Stephen's suggestion was very helpful in that it essentially confirms
what was measured before.  I have too much stuff around the rig
area,  switches and all,  and the LMR-400 seems absolutely to have
significant added losses beyond what the catalogs claim.

First item to go from the shack will be the low pass filter after
the linear and will have to decide how to simplify the rest.  Will
have to give up some present flexibility,  but certainly would be
worth that to recover nearly a dB of losses,  I think.

As to the 220 foot feed line,  anyone know of a source for
600 ohm open ladder line??  I know "we" used to build our
own (I never have!),  but my vision situation is so poor now,
the ophthalmologist has asked me to give up driving!!  Using
small tools is pretty much beyond my capability anymore,
darn it! Don't know if my posts come through with the
font's I use to prepare them -- real heavy, thick, dark,  black
letters,  hi.

Anyway,  any  leads to 600 ohm ladder line would be much 
appreciated.  I am following LB's suggestion in his post of
yesterday so searching  for  the 600 ohm ladder line.

Aloha and 73,  Jim,  KH7M
On the Garden Island of Kauai


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