LMR400 to LDF4-50A for GMRS repeater..

[ywhic]

So I got my GMRS test repeater setup almost.. (GM300 and SM50).. (yes I have my license)..

Got 1 foot sections of RG214/U with Silver Plated Amphenols with PL259 to N Male to go to the duplexer (flat pack 50w HK type)..

I have 25' of LMR400 going up to the chimney mounted antenna.. but on the RBuilder site it says to stick with Heliax.. so I found 45' of LDF4-50A for $51 shipped with factory N's on it..

I know the loss is like .661 db with the 45' Heliax where as I am at .681 with the 25' of LMR400 (both at 462mhz). which equates to 108w with the LMR400 and 116w with the Heliax with 5 dbd antenna gain..

If I cut the Heliax to 25' I would be at .368 db loss.. though I may leave that alone..

Does anyone think the LMR400 is that aweful for repeaters on here for the run from the duplexer to the antenna??? or do you think it will work fine??

I ask because weather in NJ is cold and I may not be able to do it for another month if snow gets here first..

[WA0CBW]

You would need some good test equipment to identify 1 db of difference let alone .3 db. You certainly won't be able to tell the difference by ear, even at 2db of difference. Either the hard line or the LMR would be just fine. It is probably more important that the connectors be weather proofed correctly.

BB

[prcguy]

You should always strive for the least amount of loss in your repeater feed line, a few tenths of a dB here, a dB there adds up and suddenly you wonder why your repeater works like crap compared to someone else's on the same tower.

Another thing to consider is LMR400 has had complaints of Intemod type interference, probably from the dissimilar metals between the tinned braid and aluminum foil shield. You may not notice any problem with the system described but with a really sensitive receiver, a low loss, high isolation duplexer and maybe a preamp you might notice.

If you want a high performance repeater use the Heliax and the shortest run possible and the biggest antenna possible.
prcguy

[kayn1n32008]

Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)

Cut the Hardline to the length you need, the connector is not that hard to remove and re-install.

In reality the difference between 108w ERP and 116w ERP is zero.

[rfradioconsult]

Re-using the connector on the LDF4-50 isn't a good idea, getting the center pin at the correct distance is critical, not worth the potential problems.

[LtDoc]

For the length of run that you have and at the frequency you will use them on, there will be no practical or noticeable difference between the two cables. A fraction of a dB difference isn't worth worrying about, unless you've a huge number of them...
- 'Doc

[VE6RHS]

The primary reason for recommending LDF over LMR is noise.

In a duplex situation (a repeater), noise will be heard on weak rx signals if/when the LMR cable is moved/flexed. The two metals in the shield of the cabble rubbing together will cause rx noise.

So, if the LMR is tied down so it doesn't move, the LMR is just as good as LDF for your application. However, if the LMR is subject to any physical movement (wind?), you'll hear crackling "popcorn" noise on weak signals.

[ywhic]

I ordered in a PL259 connector for the Heliax 1/2".. that way I can lose the N-PL259 adapter on the antenna end.. my duplexer has N so all is well on that end..

I may/may not cut the cable though.. I have to wait and get the PL259 in hand to see whats involved with cutting and putting it on..

I'd like to cut it to 25' just to not have the excess 20' laying in a coil inside the room.. which may be bad for it as well.. << any thoughts on that<<