Help with "Mini 8" coax please ?.....

[fires999]

Morning Guys,
Sorry to bother you , wonder if someone can help ?
Just about to install a Diamond D777 vertical antenna (designed for Civil/Mil airband) and the distance between the mounting and my receiver is between 12-14 meters - Will the 15 metre length of MINI 8 coax be suitable ?
Its for listening only , never any TX or do I need completely different coax to cover the vhf/uhf range ?
I don't want to waste money on more expensive cable if the results are negligible.

I live in the East of England , about 50km from work - I am based as a Firefighter at USAF Mildenhall (UK National but assigned to USAF) so my antenna is perfect for listening to "work " related comms !!!
Thanks in advance
Kevin (fires999)

 

[prcguy]

14 meters of mini 8 or RG-8X will loose a little over half your signal (3.5dB) at the upper end of the mil air band 400MHz. You would have about half that loss or maybe 1.5dB loss using RG-6 satellite/TV coax. There will be an impedance mismatch using 75 ohm TV coax and that will add a little more loss.

If you use LMR400 type cable you would be down to about 1.1dB loss at 400Mhz and 50 ohms to match your antenna. That's what I would do.

Morning Guys,
Sorry to bother you , wonder if someone can help ?
Just about to install a Diamond D777 vertical antenna (designed for Civil/Mil airband) and the distance between the mounting and my receiver is between 12-14 meters - Will the 15 metre length of MINI 8 coax be suitable ?
Its for listening only , never any TX or do I need completely different coax to cover the vhf/uhf range ?
I don't want to waste money on more expensive cable if the results are negligible.

I live in the East of England , about 50km from work - I am based as a Firefighter at USAF Mildenhall (UK National but assigned to USAF) so my antenna is perfect for listening to "work " related comms !!!
Thanks in advance
Kevin (fires999)

 

[fires999]

Morning PRCGUY,
Really appreciate your quick reply - so LMR400 coax over my 14 metre run from antenna to shack , I guess the figures would be slightly improved again if I can reduce the cable distance to about 10 metres ?
And please excuse my ignorance but LMR 400 is compatible with pl259 plugs ?
Thanks in advance,
Kevin

 

[jcop225]

The other piece of this decision making process is how strong the signals are that you're monitoring? A 2dB difference is unnoticeable on a very strong signal but can make a difference for weaker signals.

Another smaller 50 Ohm option is LMR-240 (same physical size as mini 8 and uses the same connectors) which would give you 2.38 dB of loss.

PL-259 connectors can be found for all of the cable types mentioned so far in this thread so that won't be a problem.

 

[prcguy]

Yes, PL-259s will fit and there are crimp and solder types. Personally, I would terminate the radio end in a female type N, then use a short jumper to the radio made with a smaller more flexible cable like LMR240 or even RG-58.

At 10 meters I would consider a run of LMR240, its much more flexible and the loss would be about 1.6dB, not all that bad.

Morning PRCGUY,
Really appreciate your quick reply - so LMR400 coax over my 14 metre run from antenna to shack , I guess the figures would be slightly improved again if I can reduce the cable distance to about 10 metres ?
And please excuse my ignorance but LMR 400 is compatible with pl259 plugs ?
Thanks in advance,
Kevin

 

[fires999]

Morning again,
Can't thank you two enough for the replies and excellent advice - I will try and find a supplier here in the UK for the 400 and 240 versions of coax , along with plugs as suggested.
Finally being able to install an antenna at home I want to make the most of the opportunity , no point putting the antenna up with proper brackets and poles etc to then screw it all up with coax cable that's no better than a length of soggy string !!!
If it's alright with you ,I will let you know what I decide to do and also the reception results...only fair as you were both integral to making it work...fingers crossed !!
Have a great weekend , really appreciate your responses and when I finish my shift at the Fire Department here on Base on Monday morning , weather permitting I will install as planned.
Kind regards,...Kevin

 

[majoco]

I know that East Anglia is pretty flat, ( I lived in Braintree for 18 years!) but IMHO 50km ground to ground is a big ask. You may want to think about a yagi pointing in the right direction instead of a 'no gain' vertical. I see the specs for the D777 top out at 400MHz so unless you actually need the airbands I would seriously consider something else or even another antenna in addition to the D777. One test is worth a thousand opinions of course but it's an expensive mistake to make.

 

[fires999]

Hi Martin,
Thanks for reply - apologies for delay but was out of touch or short while.
Antenna is mounted and works brilliantly...I am especially interested in Mil Airband 220mhz-380mhz as I am currently based at USAF Mildenhall and now I can hear alot more work traffic whilst at home , also the D777 is perfect for me trying to understand the Brazilian pirates on the old Satcom freqs around 255-265 mhz fm and the occasional military broadcast in the clear on the same freqs, albeit by mistake !!!
Hoped you liked your time in the East of England !!!!
Thanks,
Kevin