K5GO

               CABLE ATTENUATION  (dB per 100 ft)
          
                   1.8   3.5   7.0  14.0  21.0  28.0  50.0  144   440  1296
 
LDF7-50A     .03   .04   .06   .08   .10   .12     .16   .27   0.5   0.9
FHJ-7           .03   .05   .07   .10   .12   .15     .20   .37   0.8   1.7
LDF5-50A     .04   .06   .09   .14   .17   .19     .26   .45   0.8   1.5
FXA78-50J    .06   .08   .13   .17   .23   .27     .39   .77   1.4   2.8
3/4" CATV    .06   .08   .13   .17   .23   .26     .38   .62   1.7   3.0
LDF4-50A     .09   .13   .17   .25   .31   .36      .48   .84   1.4   2.5
RG-17          .10   .13   .18   .27   .34   .40      .50   1.3   2.5   5.0
SLA12-50J    .11   .15   .20   .28   .35   .42      .56   1.0   1.9   3.0
FXA12-50J    .12   .16   .22   .33   .40   .47      .65   1.2   2.1   4.0
FXA38-50J    .16   .23   .31   .45   .53   .64      .85   1.5   2.7   4.9
9913            .16   .23   .31   .45   .53   .64      .92   1.6   2.7   5.0
RG-213         .25   .37   .55   .75  1.0    1.2      1.6    2.8   5.1  10.0
RG-8X           .49   .68  1.0   1.4   1.7    1.9      2.5    4.5   8.4
 

The case for using 3/4" CATV Hardline

3/4" CATV hardline can usually be obtained for free.  This coax has approximately 1/4 the loss of standard RG-213 and has just slightly more loss than 7/8" heliax.  Gain is too hard to obtain and too easy to give up. 

Connectors to adapt to UHF are easy to make and inexpensive.  A plumbing adapter that has a 1/2 inch (not threaded) opening at one end and an inside threaded hole that measures approximately 3/4 inch at the other end is what you will need along with a Amphenol PL-258 (double female UHF).  Some of the other brands of PL-258 connectors are a little small in diameter and will recess into the copper fitting too far.  The amphenol ones work perfectly. 

The best way to do it is to remove the retaining ring that holds the guts of the PL-258 so you can take them out while you solder the connector in the copper fitting.  it can be tedius using a dental tool to remove that ring.  I have found that a cup of water, a pair of pliers and a quick hand can make it possible to solder the connector without melting the dilectric.  

Use a propane torch to solder around the top of the copper fitting where the PL-258 enters the opening.  Make sure the solder flows all the way around.  Make a square cut oin the end of the CATV hardline.  Use a tubing cutter and remove about 5/8 inches of the aluminum jacket and the foam surrounding the center conductor.  Make sure to scrape the center conductor to remove all the foam.  If you start the connector straight, it will cut its own threads as you install it with an open end wrench.  Thread it on as far as you can, remove it, wipe off any metal shavings, apply NOALOX grease on the threads to help prevent corrosion from the dissimilar metals and then put it back on.  

Series matching sections are easy to make to convert from 50 to 75 ohms.  See two links on this website for further information - W8WWV website (SMC program) and the Twelveth-Wave Matching Transformer article by Darrel Emerson  

Another option is to cut the coax to a length that will provide a multiple of a half wavelength on each of the bands you will be using.  You will have an inherent 1.5-1 SWR and the loss associated with that SWR for the length of coax used, but the impedance will be repeated from one end to the other to make your transceiver happy.