Is it possible for two operators to work from the same peak, same band (eg 20m ssb, 5 watts)) succesfully and not interfere with each other?
If people do this, what spacing, both physically and frequency-wise do they use?
The antennas in use by the two potential ops are an inverted V and a vertical whip with radials.
Thanks for any comments.
Ian VE6IXD
In reply to VE6IXD:
I don’t think so. You’ll have interference.
We tried one in CW and the other SSB and the SSB transmissions were giving the CW op a hard time. Now maybe the SSB was a little more then 5 watts.
In reply to VE6IXD:
Hi Ian,
Yes it can be done but it depends on having clean transmissions and strong front ends - the preamps might have to be put off. Also you can drop the power below 5 w dramatically reduce interference and still make contacts. I have operated CW within 50 kHz of another CW station with acceptable interference. We were about 40 m apart.
I have also operated on SSB but got unacceptable interference from a station 200 m away and only 20 kHz up the band.
I recommend getting on opposite sides of the peak preferably so the antennas are screened from each other and getting 100 kHz or more apart and trying to use different modes.
SSB signals are more easily over driven and so cause splatter(don’t shout) so CW has some advantages. If you can operate on different bands then the ops will of course interfere less.
Otherwise you could take it in turns to use the same frequency and mode but using your own stations.
Or one could carry lunches etc and the other the station and share both.
Many possibilities.
73
Ron
In reply to AX3AFW:
It comes down to blocking - and despite what Ron says, CW from a nearby transmitter sounds clicky and causes the AGC to pump. You need as much separation as the band will permit, switch out the RF amp, switch off the AGC, turn AF gain full up and control volume with the RF gain. This will give you a fighting chance…but no guarantees! I have a nearby CW operator so I have experience!
Brian G8ADD
In reply to VE3IXD:
My experience with this type of operation with vk5pas on ssb and vk5cz on cw on 20m . Both using a link dipole and 5 watts with 100m of separation interfered quite badly. On the next Summit Paul had his 20/40 link dipole I used my 20/40 Par end fed and no interference at all which surprised us. Both antennas were radiating because we both made contacts. Working that close my CW on 15m was breaking into Paul who was on 40m ssb as well. But give it a try and take turns if it’s no good, no point over loading the front ends for the sake of a few minutes of operating .
good luck de Ian vk5cz …
In reply to G8ADD:
Hi Brian,
Yes your suggestions are good but I’ve not had to go to those extremes. Your neighbour is probably running a tad more than 5 watts and maybe you are not more than 100 m apart both of which change the situation. Key clicks? Gawd I thought we knew how to suppress those. I’ve not heard any from FT817’s or KX3’s in my vicinity with 20 kHz separation. However the background noise rises and the closer you are to the other guy’s frequency the worse it is likely to be. Digital VFO’s!
The overload effects are power level sensitive and not in a liner manner so dropping from 5 W to 2.5 W will drop your signal by 3 dB but the interference may drop 10 or more dB.
As Ian VK5CZ says sometimes its a problem and sometimes it isn’t. Antenna alignment can be useful in dropping the interference significantly.
73
Ron
In reply to VE6IXD:
Would working on 20m/40m then swapping work? Or would there also be harmonics?
de va6mcb Walker
In reply to VA6MCB:
Hi Walker,
Yes there certainly are harmonics and whether they are 40 or 60 db down doesn’t matter, they are strong enough to prevent using that frequency. It’s not just the second but the third and fourth harmonics that are LOUD. It’s only a small bit of the band so it’s not a problem unless the other rig has spurious emission problems or your receiver is a DC type with limited rf selectivity and poor strong signal rejection.
Not all of the band is available for QRP SOTA operation anyway. For example a strong signal from a home station that is line of sight but many km away will also “lock out” a bit of the band so it’s no big deal.
73
Ron
In reply to AX3AFW:
Thanks Ron, sounds like SOTA will continue to be solitary for HF activators.
Excuse my ignorance but do HT handies suffer the same problems or with highly directional antennas is sympathetic resonance prevented. It’s hard to imagine how SOTA activators cope in Europe, at least here there is no chance of a crowded summit…
It’s not a purely hypothetical question as I hope to visit the UK this summer, ( CEPT willing) and wonder what happens on summits with multiple operators.
In reply to VA6MCB:
Hi,
There is no need for SOTA to be solitary, indeed from a safety in the outdoors aspect three people is a good idea. A little bit of QRM in parts of the band is not a problem. In VK lately we have maybe 5 - 10% of activations involving two stations on the one peak at the same time. Hasn’t been any disputes. Recently we had four HF stations on the one peak within a straight line of less than 300 m and we all got plenty of contacts with minimal interference. Two FT817 and two KX3 rigs, antennas were dipoles, EF, tuned doublet.
I don’t use a hand held much but some sets have a reputation for being blanked out by commercial rf services on the same peak. That is likely to be the main issue. I’ve not heard of problems with dual activations but obviously both can’t use the same frequency simultaneously.
Re Europe, I haven’t seen many alerts with different operators on the same summit at the same time but have read of it happening on posts.
Friendly amateur co-operation is as always the key to a happy operating period.
Most AR operators are friendly and SOTA ops are even more so. After all both of you have struggled up to the top so there is something in common for starters. Just don’t spend too long chatting before you get on air and have at least 4 calls in the log.
Good luck.
73
Ron.