Loss of Wireman 553 windowed ladder line at MF/HF – does it matter #2

Loss of Wireman 553 windowed ladder line at MF/HF discussed the matched line loss of a windowed ladder line with 19 strand CCS conductors.

Clip 094

Above, the loss curves from the article

You might look at this and ask “does it matter”.

A recent thread on QRZ (Any special consideration for long run of twin-lead?) gives an interesting example. Continue reading Loss of Wireman 553 windowed ladder line at MF/HF – does it matter #2

Loss of Wireman 553 windowed ladder line at MF/HF – does it matter

Loss of Wireman 553 windowed ladder line at MF/HF discussed the matched line loss of a windowed ladder line with 19 strand CCS conductors.

Clip 094

Above, the loss curves from the article

You might look at this and ask “does it matter”, if 10m of this line is used in a G5RV, 0.0075dB/m at 3.6MHz gives 0.075dB loss… that is just 2%, so what.

That ‘back of the envelope’ calculation is incorrect, that feed line section operates with standing waves and the loss under standing waves must be evaluated. If we took the feed point impedance of the popular G5RV to be around 10-j340Ω at 3.6MHz, the expected loss in 10m of Wireman 553 with that load based on the above MLL is 3.3dB or 53%. By way of contrast, my own G5RV uses 10m of home made open wire line using 2mm copper wires spaced 50mm and the loss is 0.9dB, 2.4dB less. Continue reading Loss of Wireman 553 windowed ladder line at MF/HF – does it matter

Loss of Wireman 553 windowed ladder line at MF/HF

Over a long time I have voiced concern at the likely performance at MF / low HF of the very popular windowed ladder lines that use CCS conductors.

A very popular form of commercial ladder line is that using #18 wire, comprised of 19 strands of #31 30% IACS conductivity copper clad steel. The copper cladding on such a conductor is about 14µm in thickness.

This article reports and analyses measurements of a length of Wireman 553 windowed ladder line. Continue reading Loss of Wireman 553 windowed ladder line at MF/HF

AIM 882 produces internally inconsistent results

 

AIMuhfI have had cause to validate the output produced by an AIMuhf measurement using AIM882 (current version, released about three months ago).

The test scenario is a pair of nominal 50+j0Ω loads on a Tee piece, connected to the AIMuhf by about 1m of RG58 coax and swept from 10 to 50MHz.

Screenshot - 16_01_2015 , 15_40_27

It is mental arithmetic that the VSWR should be very close to 2:1, and since the loss of the cable is quite low, VSWR should be almost uniform with frequency. Continue reading AIM 882 produces internally inconsistent results

BNC 75/50 compatibility

One sees perennial discussion in ham circles of compatibility of ordinary 50Ω and 75Ω versions of the BNC (Bayonet Neill–Concelman) connector, in particular the risk of damage in mating a 50Ω and 75Ω pair.

But are there incompatible connectors commonly in circulation.

These discussions often seize on the different dimensions 0.7mm and 0.9mm.

BncPinAbove shows measurement of the centre pin diameter of a Kings BNC connector (for RG58), it is 1.339mm… nothing like 0.7mm or 0.9mm. (Amphenol Connex 2001) gives the centre pin diameter as 1.32-1.37mm. Continue reading BNC 75/50 compatibility

Where is the best place to measure feed point VSWR

The subject question is often asked, and the usual responses are mindless recitals of Rules of Thumb (RoT).

In the light of the discussion at Feed line length affect on VSWR and The half waves of coax rule for measuring VSWR accurately, lets consider the subject question and develop a rational answer. Continue reading Where is the best place to measure feed point VSWR

The half waves of coax rule for measuring VSWR accurately

Lots of hams recite a rule that accurate measurement of VSWR can only be made at the feed point or an integral number of electrical half waves from the feed point.

It is one of those ‘rules’ that the proponents cannot usually explain… they would regard themselves as experts, but blindly follow folk-lore that they do not understand. Continue reading The half waves of coax rule for measuring VSWR accurately