Noted with thanks - it is as you describe so I'll add VFO stability and linear requirements to the list...

Hi,

I'm getting stuck into a new project that will involve a 20 or 40 metre QRP transmitter (a few watts is sufficient) capable of transmitting DominoEX.
 
I do a fair bit of construction but I haven't gone down the homebrew transmitter route before so the space is entirely unknown to me; I'd appreciate a steer from anyone to either a good transmitter design or (even better) a suitable kit.

Thanks in advance
Cormac, EI4HQ
[Cobh, IO51uu / UTC+1] NNNN++++

Hi,

I've been licensed since 1993 and I've been almost exclusively a CW operator. Recently I've begun spending more time on SSB. This morning I worked a DL special event station (DR11BUGA) and many stations were signing '44s' with him. What does 44 mean? I've never heard it on CW... On the web I found; "44 - Answer promptly by wire"

So does 44 mean electronic QSL?

BR
Cormac, EI4HQ
[Cork / UTC+1] NNNN++++

Hi All,

Quick question. I'm in the situation of many many others in having my shack on an upper story. Now I've NEVER had any RFI issues. I have a 'serious' amount of copper in use inside and outside the shack and I'm using balanced antennas with common mode currents dealt with as far as practicality allows. However when all is said and done my 'RF ground' (sic) has to travel a distance of 4.14m from shack to ground rods. It's a 9" wide copper strip. Regardless, it's clearly going to show a high RF impedence at higher HF frequencies...

My question is driven more by curiousity than necessity (I stress again I don't have any apparent problems); my ground is:

• x1.6 quarter waves on 10 metres
• x1.4 quarter waves on 12 metres
• x1.2 quarter waves on 15 metres
• as near as dammit a quarter wave on 17 metres (clearly pretty uselss there)

On 10, 12 and 15 metres, is there any effective RF grounding taking place, or is an RF ground basically useless on all higher frequencies once the ground length exceeds a quarter wavelength?

Thanks in advance.

BR
Cormac, EI4HQ

Hi All,

Thanks for input from all contributors. I thought I'd provide an update on how things actually worked out...

In the end I had to mount the antennas with A270 at the top, A50S in the middle and the TH3 Mk IV at the bottom. I tried the A50S at the top and the A270 in the middle, but the wind loading would not have been acceptable so I had to swap them around. The vertical distance between each antenna is about 4 feet and all booms are parallel.

First, the good bits; the A270S tunes as per spec., the TH3 Mk IV tunes as per spec. on 15 and 10m.

The bad bit is the A50S is resonating 1.3MHz above spec. (approx. 51.4Mhz instead of down around 50.100MHz) and the TH3 Mk IV is resonating 500KHz above spec. on 20m (14.550MHz instead of around 14.050Mhz). The TH3 Mk IV is showing an SWR of just under 2:1 at 14.010MHz and the A50S an SWR of about 1.5 at 50.100MHz. There appears to be interaction between the two antennas; I temporarily removed the A50S and the TH3 Mk IV then behaved as per spec. on 20m.

While not ideal on 20m/6m, and goodness knows what the radiation patterns look like, the setup is very usuable with the greatest compromise on 20m - since installation I've done some test driving on 20m and it's working well enough to satisfy me... As I'll be removing the A50S for each Winter season anyway, the compromise is quite acceptable.

Thanks to all for your insights/contributions.

BR
Cormac, EI4HQ

Tom,

Words of wisdom - as you say - we tend to look for the 'easy' answer knowing full well there probably isn't one ;-) The triumph of hope over experience...

Your suggestion is a good one - its easy enough for me to give different mounting scenarios a go and see how things shape up - I'll start with that one (TH3 at 0m, A27010S at 1m and A50S at 2m) and see how it looks.

BR & 73
Cormac

Hi,

Space at towertop available for antennas is only about 2 metres (6' or so). This is a design decision due tower limitations and allowances for bad winds at QTH.

I have 3 antennas:
1. TH3 Mk IV (3 ele tribander)
2. A50S (5 ele for 6m) and
3. A27010S (5 ele on 2m & 5 ele on 70cm).

I'm worried about the negative consequences to any/all antennas by close stacking...

In theory I could mount all 3 separated by circa 1m (TH3 at 0m, A50S at 1m and A27010S at 2m), but I expect that would result in 'significant' radiation pattern distortion and/or tuning issues for each/all of the antennas?

I'd appreciate the insights of those who've close stacked antennas, and some idea of how 'bad' the consequences are likely to be...

Thanks in advance
BR & 73
Cormac, EI4HQ

Hi,

I'm currently finalising details for my new tower. I've a significant interest in utility listening and the 'icing on the cake' will be 4 RX only antennas right at very top of the tower, above the HF beam. The 4 antennas will be :

1. Marine VHF (156-162 MHz)
2. Marine AIS (circa 162 Mhz)
3. ADS-B (2 GHz)
4. Airband (118-136 MHz)

1,3 and 4 will be simple vertically polarised dipoles - gain is not an issue. 3 is already taken care of with a commercial grade antenna.

My question is this: does anyone have a proven 'bombproof' homebrew VHF dipole design that will remain watertight and survive 90 knot winds for extended periods?

These antennas will be quite inaccessible and I want a design that will last many years without maintenance...

All suggestions welcome...

73
Cormac, EI4HQ

Dan,

Thanks for running the EZNEC model to give me a clear answer. I'm just getting to grips with EZNEC, and I haven't yet quite worked out how to put the capacitor, at the feed end of the inverted L, into EZNEC.

After some messing around, I decided that as I was putting the antenna up, I might as well do it properly. Hence, I've gone the extra mile and mounted the end at about 40 feet. I reckoned the extra height wasn't going to do any harm anyway :-)

Like you suggest, I can't really see any noticeable change on the antenna analyser, & the big issue is the earth - the analyser readings indicate I've alot to do there still... well begun however...

Rgds
Cormac, EI4HQ

Hi,

I'm installing an inverted L for top-band. The vertical section is approximately 57' & the horizontal section is circa 120' - it'll be cut to tune.

My question: From a performance point of view only, is the height at which the horizontal section end is supported, important?

I can easily support the end at a height of about 25', but I could go an extra 15' with some extra hassle - from a performance perspective is the extra 15' worth the extra hassle?

The antenna will be used almost exclusively on TX, I have separate RX antennas.

Rgds
Cormac, EI4HQ

Thanks to one & all for info. provided.

I had a feeling there was a fatal catch - like was pointed out, just because it loads don't mean it'll be any good.

After I posted, it dawned on me that I had a copy of EZNEC somewhere. I dug it out & I modelled the system. As was pointed out the main lobe is somewhere in the 50/60 degree range. Coupled to the polarisation issue, its basically hopeless, as you've all advised.

Case closed. I was never considering it as a serious candidate for a 6m antenna, but I'm an inverterate tinkerer & had to know. I'll build a decent beam one of these days.

Rgds
Cormac, EI4HQ

Hi,

I only recently got a rig that has 6 metres on it, and I currently don't have an antenna for that band.

I was messing around in the shack the other day and for the heck of it I checked to see if any of my existing antennas (individual ground mounted verticals for 160, 80 & 40) would tune up on 6m. Interestingly, the 40m GP tunes very nicely - without an ATU in-line the SWR is 1.3 at 50.0MHz and 3.1 at 51.1MHz. Very useable on CW, and across the band with an ATU in-line.

the 40m GP is approximately 2 wavelengths long on 6m.

My questions are these:
1. What will the radiation pattern look like?
2. Does it have some gain?

Unless I've missed something, the ARRL Antenna Book doesn't discuss the behaviour of ground mounted vertical antennas when they are multiple wavelengths long... are they behaving as 'long-wires' in this situation?

Rgds
Cormac, EI4HQ
IO51UU

Don,

The HTX100 was my first rig, purchased in Florida while I was working /mm out of Fort Lauderdale. Like WB2WIK it served me very well at the peak of cycle 22. The drawbacks are small, but for me the biggest was always that it didn't do FM - for a mobile this was a significant omission in my opinion.

Since 1999 the same HTX 100 has been the heartbeat of EI0TEN, Ireland's 10 metre propagation beacon (28.209MHz). Its been operating 24 x 7 x 365 almost continuously since then, at full output power, without so much as breaking a sweat. The HTX 100 is popular with the beacon crowd as its cheap, cheerful and very reliable.

If you can get one without parting with too much cash - go for it.

Rgds
Cormac EI4HQ

I'm a merchant sailor turned computer science researcher who happens to be a ham as well... Hence the following 'might' make some sense ;-)

I want to have a go at decoding a transmission mode called Gaussian Minimised Shift Keying (GMSK). This is the mode used by shipboard UAIS (Universal Automated Information System) transponders. For information on UIAS see http://www.ais.org.

I'm not aware of any software that can decode GMSK transmissions. If there is, I'd love to hear about it!  Alternatively, I'm looking for technical information about how to program a soundcard, preferrably under Linux. I'm apathetic about programming language, any will do.

Thanks!
Cormac, EI4HQ

Hmmm,

I had a look tonight, and while the mod is reversible, as you say it involves hacking at a PCB...

I'm a little concerned about the magnitude of the change proposed by the mod: a change in AGC delay from 2.2s to 11.6s is 6 times... did Kenwood get it that wrong? ;o) Also I can only find that one reference to the mod; did this guy dream it up?

I'm going to read around a bit more and see what else I can find out before deciding whether to carry the mod out or not.

I agree with the difficulty that exists with listening to the radio for extended periods on busy bands: I've been on 40m this evening for a couple of hours and my ears are ringing...

I'll post again once I've looked around some more.

Cormac EI4HQ