[TowerTalk] Need help estimating cable length of DXE 400 MAX

[Michael Tope]

Yeah, I just did that with a large reel of RG6. I just stripped the 
cable back so about 1/4" of center conductor was exposed. I pushed the 
exposed center conductor into type-F jack of the adapter on my MFJ-269 
far enough that part of the annular ring of the shield touched the outer 
conductor of the type-F jack. I was a little surprised, but this was 
good enough to get frequency readings for two adjacent impedance minimums.

Short clip leads work pretty well, too. Somewhere I have a couple of 
PL-259s that have clip leads attached to the back side for that sort of 
thing.

73, Mike W4EF.......................

On 1/12/2020 11:14 AM, jimlux wrote:
> On 1/12/20 10:24 AM, David Gilbert wrote:
>>
>> If you have an antenna analyzer that can measure complex impedance 
>> (as in R +/- jX) and if you are willing to put a connector on one end 
>> of the cable, I can tell you how to get an accurate length 
>> measurement using TLW, the transmission line application that comes 
>> free with the ARRL Antenna Book.  You don't need an instrument with 
>> TDR capability (Time Delay Reflectometer) to do it.
>>
>> 73,
>
>
> I'll bet you could do it without a connector and using clipleads. it's 
> probably around 200 ft long (60 or so meters, maybe 80 meters 
> electrical length, depending on the velocity factor)
>
> So a few inches or feet won't make much of a difference.
>
> You tune the antenna analyzer until you get a peak in SWR - that will 
> be a multiple of a quarter wavelength. If it's an odd multiple of 1/4 
> wavelength, the open at the far end is transformed to a short at the 
> SWR meter end. If it's a even multiple of a 1/4 wavelength (multiple 
> of 1/2 wavelength), the open at the far end shows up as an open at the 
> meter end.  Both are "infinite SWR".
>
> if you sweep around 1.8 MHz and you get that peak, that's probably the 
> 1/2 wavelength scenario. and so forth.
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk