PORTABLE VS FIXED VHF RADIOS

Graeme Street · Post by **Graeme Street** » Thu Jan 12, 2012 9:14 am

I have an Icom A2 installed in my Jodel D120 with a two place intercom. The radio is powered from the aircraft electrical system and a coax cable runs to an antenna on the fuselage. A grounding plate is fitted. David Clark H13.4 headsets are used.
The reliability of this arrangement does not meet with my expectations in that occasionally transmitting is not readable by ATC. This problem appears to be worse when two headsets are used. As I operate from a strip within Class D airspace a reliable radio is a must.
Is it reasonable to expect this system to be able to perform to a level equivalent to a radio designed for fixed installation? The A2 transmits at 1.5 W (carrier)/ 4.8 W (PEP). Typical fixed installation radios transmit at 5 W (carrier?) and above. This suggests the A2 performance will never consistently match a typical fixed radio. Quality radio performance (clarity, range & quality intercom) for me is a priority. Comments?

Rod1 · Post by **Rod1** » Thu Jan 12, 2012 10:03 am

I have not used an Icom A2 but based on two Hand held’s I have had in the past I always got “ok” results. What sort of range do you need? I found much over 15nm could not be guaranteed. Now have a conventional panel mount BK and it is as good, if not better, than my old C of A machine.

Rod1

Graeme Street · Post by **Graeme Street** » Thu Jan 12, 2012 11:34 am

Rod1 - I would expect at least 20 nm range, which is typical of what I used to experience in CofA aircraft in my area.

gasax · Post by **gasax** » Thu Jan 12, 2012 12:23 pm

I had a nearly identical installation in a CH601 - but using a microavionics intercom. It had very good performance - consistently out-perfroming the CofA aircraft I toured in company with.

A little investigation with a signal strength meter might make sense. Bonding and the size and type of the backing plate and antenna can make a very big difference - of course the Ch601 is all aluminium so ....

mcfadyeanda · Post by **mcfadyeanda** » Thu Jan 12, 2012 1:50 pm

I've had excellent performance with a similar arrangement (A20 rather than A2), even operating at the low power setting of 1.5W PEP; better than many CofA installations!
The downside is that on London Information (for example) higher power transmitters will always step on you.
Who is going to point out that the original CAA Class of approval for this handheld does not permit use in Class D?!

Duncan McF.

John Clarke · Post by **John Clarke** » Thu Jan 12, 2012 4:13 pm

I also have a CH601 fitted with a handheld, in this case an Icom ICA-22. I've always had perfectly acceptable results from it.

Transmit power makes less difference than you'd think. I doubt if ATC or anyone else could tell the difference between 1.5W and 5W, especially if your strip is close to the ATC unit you need to talk to.

In what way do ATC tell you the signal is unreadable? Weak voice, interference from ignition or strobe systems? Could be worth trying it with a friend in another aircraft (perhaps even record the transmission so you can hear the result).

It could also be worth getting the radio checked to make sure the modulation level is set correctly and that it is exactly on frequency.

Dave Evans · Post by **Dave Evans** » Thu Jan 12, 2012 10:00 pm

Graeme,
I've got a handheld Icom A2 in my D112, wired into a fixed VHF aerial and 12v 7aH battery power supply on a cradle between the seats. Works like a dream with range in excess of that expected from a handheld. I think the correct aerial installation is the key to the radio range. However, even though it works extremely well, I'm soon intending to fit a fixed VHF installation, probably a Becker AR6201 just because it will be 8.33 complaint and looks better in (or rather, under) the panel.

PS. I've found that when transmitting through the portable intercom box, the signal is not quite as clear. As I tend to fly on my own a lot, i normally connect headset straight into the Icom

cardiffrob · Post by **cardiffrob** » Fri Jan 13, 2012 8:50 am

I've been asking some Engineers about ground planes. If one has a 1/2 wave (3 foot-ish) aerial then do you need a ground plane under it? If so, does it have to be flat or can it curve down the side of a rounded fuselage?

Any ideas?

Valcom 760 panel mount. Seems to receive TWR from about 7 miles away whilst on the ground, so long as the fuel pump is off. Grrrrrrrrrr.

tnowak · Post by **tnowak** » Mon Jan 16, 2012 8:09 am

All antennas need a ground plane. If your aircraft is of aluminium construction, then the structure provides the ground plane. If aircraft is wood or composite then you need to add a ground plane.

Doesn't matter that much if the ground plane is curved. Aluminium foil (the thicker variety) will make a good ground plane.
Tony N

mikehallam · Post by **mikehallam** » Mon Jan 16, 2012 12:56 pm

A true 1/2 wave Ae.does NOT need a ground plane. Just not often seen on a/c ?
A 1/4 wave or a wound facsimile does need one. Can be a sheet of foil, a cross or more of wires;

or in my case the ali fuse of a fabric Rans seems to work perfectly well.
& a 'hand held' Icom or similar - using power from the a/c 12volt.

mike hallam.

Ian Melville · Post by **Ian Melville** » Mon Jan 16, 2012 5:53 pm

A true 1/2 wave Ae.does NOT need a ground plane. Just not often seen on a/c ?

Europas have a 1/2 wave in the fin. Copper tape glassed in.

I've been asking some Engineers about ground planes. If one has a 1/2 wave (3 foot-ish) aerial then do you need a ground plane under it? If so, does it have to be flat or can it curve down the side of a rounded fuselage

That sounds too long for one element of a 1/2 wave dipole(1/4 wave monopole). though you could have 1/2 wave monopole? Is the cable fed to the middle, or end?

If middle then no groundplane required and it should stand on it's end, however I think it more likely it is fed to the end, in which case it should be 56cm long and will require a groundplane of thin ali sheet or mess 56-60cm dia. Curve is no problem.

Have you lot not read the latest LAA magazine

Roger Camp · Post by **Roger Camp** » Tue Jan 17, 2012 10:22 am

Good morning folks, many years ago when the CB radios were all the scream, we set up the antenna to the radio with a Standing Wave Ratio meter. (SWR). As our Radios are transmitters, then the aerial has too be adjusted to the tranny. So maybe find out who the local radio ham is and get him in on the matter. He can set up the SWR as they have all the gear to do it with.

The comments about the ground plane are very important and are an absolute must.

The worst you could do if the SWR is off is wallop the output stage of a perfectly good radio. (ouch bite me)

cardiffrob · Post by **cardiffrob** » Tue Jan 17, 2012 6:15 pm

A true 1/2 wave Ae.does NOT need a ground plane

Curve is no problem.

If we are all agreed on this then I'll fire it up and find a radio ham.

Have you lot not read the latest LAA magazine

Yup! Not answered in there.

Cheers!