Just a guess on my part, but one of the ARRL books lists 76 feet as a
non resonant length for guy wires. Maybe the antenna guys are trying to
hit a "good" length for the coax. Maybe not to improve anything, but
to prevent a problem on a particular band.
I know from my own experience (and that of others) that adding a short
coax jumper to increase the length a bit will make a finicky band tune
better.
Or it just may be that's how much coax he had laying around the first
time, and since it worked , that became the length. Or it was just
considered enough to get from point A to point B.
73, Steve KW3A
On 8/20/2012 7:23 AM, Lou Kolb wrote:
> Colin,
>
> The minimum 70 feet is a specification from W8AMZ, whose version of the G5RV
> Howard and I are using. I have no idea where that comes from nor do I think
> it's meant to be a universal spec for all G5RV's. I imagine he has his
> reasons for such a spec but I haven't seen them listed anywhere. When I
> bought the coax for mine, I just happened to get a 75 foot run to make sure
> I'd have enough. Then, when I bought his version, I saw his requirement and
> just left the coax in tact even though I don't need that much. Lou WA3MIX
> Lou Kolb
> Voice-over Artist:
> Radio/TV Ads, Video narrations
> Messages On-hold:
> www.loukolb.com
> ----- Original Message -----
> From: "Colin McDonald" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, August 20, 2012 12:09 AM
> Subject: Re: Tom's G 5 R V
>
>
>> granted, the recommendation for using 75 feet of 50 ohm coax is something
>> your antenna designer stated.
>> However, most antennas based on the G5RV design do not specify a certain
>> length of 50 ohm coax to feed it.
>> Where does the magic number of 75 feet come from? it's not a quarter wave,
>> or a half wave on any of the frequencies the G5RV style antenna covers...
>> I've now seen several installations where a short pig tail, or any various
>> length of 50 ohm coax is used and the antenna plays perfectly fine.
>> does the extra long length of coax somehow reduce swr or increase
>> bandwidth
>> or make the antenna more efficient? I would think any gain in efficiency
>> would be off set by loss in the coax over 75 feet.
>> those are just my thoughts.
>> But if you have a technical explanation as to why they work better with 75
>> feet of coax, please explain if you would.
>> I'm curious to know why.
>>
>> 73
>> Colin, V A6BKX
>> ----- Original Message -----
>> From: "Howard, W A 9 Y B W" <[log in to unmask]>
>> To: <[log in to unmask]>
>> Sent: Sunday, August 19, 2012 7:51 PM
>> Subject: Tom's G 5 R V
>>
>>
>>> I have been out of town until about an hour ago. I just read all the =
>>> posts in regard to your antenna Tom.
>>>
>>> For the antenna to work properly you need about 75 feet of coax between =
>>> the window line and your radio. The excess coax can just be coiled up =
>>> in your shack or outside the RV at a convenient place.
>>>
>>> I know you really don't need to buy a new antenna, however, the G 5 R =
>>> V's from W 8 A M Z are made very well. The connections at the top where =
>>> the window line connect to the two legs of the antenna are sealed in =
>>> epoxy. The bottom end of the window line is terminated in an S o 239 =
>>> connector which is also sealed in epoxy therefore all the connection =
>>> points will not get any moisture in them. The 450 ohm window line is =
>>> copper coated steel wire which is insulated and will not break from =
>>> movement in the wind.
>>>
>>> I own one of these and I feel it is of high quality. The regular size =
>>> is about $70.
>>>
>>> Get the wire off the ladder, cut the P L 259 connector off the coax =
>>> pigtail check for continuity. If there is still a short, cut the =
>>> pigtail completely off the window line and make a new pigtail and =
>>> install it be sure to water proof all connections.
>>>
>>> Again, 75 feet of coax between window line and radio, a must!!!
>>>
>>> In general, it seems like most agree on what you should do.
>>>
>>> 73
>>>
>>> Howard #3
>
>
>
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