Antenna Connection Question

[Brandon Whitman]

Hello, 

I am new to the hobby and working on my Foundation license, so this question is purely about being able to receive and listen.

I have purchased a Yaesu FT-70D as well as a SQBM110 MkII Dual Band 2/70 Vertical (N-TYPE) Radial Free (https://moonrakeronline.com/sqbm110-mkii-dual-band-2-70-vertical-so239-radial-free?___store=default) antenna. I know I need an SMA to BNC adapter to use this antenna with the handheld, but my question I'm hoping someone can help me with is what kind of cable do I need to purchase?

Thanks so much and appreciate any advice! 

Brandon

[JJ (g6vzm)]

How will you be mounting the aerial and how far from the connector will you be operating the handheld as that will dictate the quality of cable required?  Also, you'll need to adapt from SMA to N-Type, not BNC, and it's really best with a handheld to use a short tail (say 50cm) of lightweight (but efficient) coax with the different connectors on rather than an adapter to avoid the weight straining the connector on the radio which may only be secured inside by soldering to a PCB.

JJ

[Brandon Whitman]

The plan is to eventually get the aerial on my roof and operate handheld from inside the house, so maybe 50 to 75 ft of cable? Thanks for the correction on the adapter, I’ll change that. 

Do you have links from a site like Moonraker that you could link the short tail and and high quality coax as it is all still a bit foreign to me?

Thanks,

Brandon

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Brandon Whitman Director Product Analytics +44 7752 370690 brandon...@pipedrive.com 4 Kingdom Street, Paddington, London W2 6BD, United Kingdom

[JJ (g6vzm)]

50-75ft (or can we call it 20m) is a long distance at 70cm/430MHz because the cable loss increases with the frequency so while for an arbitrary theoretical cable the loss at, say 10m/30MHz might be 3db (and even that's half your signal strength), at 70cm it could be 12-15db, or most of your signal.  For other than industrial use, Messi & Paoloni make some of the best cable available in the UK and they have some comparison tables on their website: https://messi.it/en/comparison-chart-50-ohm-cables.htm  One of their illustrations is their Ultraflex 7 vs. RG213 and another their Ultraflex 10 vs. RG213 which shows 11.8db loss/100m in the Ultraflex7 and 8.3 for Ultraflex10, or just over or just under 2db for the distance in question.   With aerial feeder it's safe to say that you get what you pay for and the sky's the limit.

I'd start by giving Moonraker a call and see if they stock M+P and can make you up an adapter, but if they can't then it's Martin Lynch in Staines who are an official UK distributor.  Alternatively, if you want to just try something out, and you're around Paddington as your signature suggests, then come along to the space sometime as we have a load of RG213 type cable surplus to requirements which would get you started.

Thinking beyond the foundation licence, there are obviously a number of quality radios for VHF/UHF from the usual suspects and many quite reasonable Chinese generics that will take you to the maximum power at Intermediate level where the feeder loss won't be so detrimental.  Again, you get what you pay for but there are some surprisingly good cheap radios in the 25W mobile class.

Do you have a date for your Foundation exam yet, because we could probably schedule a revision/crammer/question spotting/exam advice session for you if you think it would help.

Regards,

JJ

[Brandon Whitman]

Hi JJ,

Thank you so much for the detailed response! I will give Moonraker a call and see if we can sort that out. At the end of the day (at least right now) my wife and I would love to listen to the airplanes coming into LHR as we live right in Kew and see them fly over the house. 

I really appreciate the offer on the crash course for Foundation license as well, that would be fantastic. I'd also love to see space and check out the equipement. Is there a day of week / time that would work best to schedule the cram session or see the space?

Best, 

Brandon

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[JJ (g6vzm)]

Best thing is if you can make our next regular meeting, this coming Saturday between 14:00 and 16:00 but note that I have to be away very promptly this month.

Note that the FT-70D is FM and C4FM while aviation uses AM so you won't be able to receive aircraft directly (a cheap SDR might be a worthwhile investment) but there are ground relays at LHR although you'd need a bit of height to pick them up.

JJ