Saturday, April 11, 2015

4m 70MHz spring es in the air.. why should I ?

While in South Europe  TEP at 6m and even 4m  is possible since many months.
We only have FSK441 in MS or tropo being too far from Equator. at 53N
Contacts in FM  at 70.450MHz  with other 4m stations over 200km is possible regular there is some activity at 4m in FM

The DK7ZB 3 band 2 4 6 meter antenna is performing very well but I have extended  my HF 4 band dipole with a 6m 4 ele that outperforms the 2 ele of the 3 band VHF
The 6m part of this 3 bander is now causing a problem
The 4M preamp is blown up when transmitting 6M high power on the 4 element.
To much power is coupled back into the other antenna.
I replaced the 3 band  VHF mini beam with a 4 ele mono band  beam.
But that one has high SWR since I copied the 12.5 Ohm design last year.
Does receive well but transmitting is a bit a problem with the bad matching.

A new 4 meter antenna  is in construction  and almost ready to fire up.

A DK7ZB  design  5ele 50Ohm
Constructed as light as possible  using square alu tube boom 20x20 and 10mm elements.
It has to be placed  close to the HF/6m antenna so the design has to be not critical 50Ohm
My previous 8/7 ele 4/6m duoband Yagi was a complete failure but it left me with lot of  antenna stuff in stock.
I hope this antenna does perform well.  I trust Martin DK7ZB design's

Single Stauff per element The M4 bolts are isolated and filled up to fit better in the Stauff 6mm holes
Short pieces of 6mm black pneumatic tube is used for that.
If this antenna performs well I give a party  Hendrik Jan beer is available!
Radiator using 3 Stauff clamps 1 cm air gap. The element halves are terminated with M4 bolts
These bolts fix them apart as well.
Whats left is connecting the coax cable through some ferrite rings as balun and it should be ready to lift to 24m a.g.


320 long  20x20mm boom seems stable enough.
With a square boom it is much easier to line up the elements.
The 7/8 elements 6/4m combi I have build 2 year ago with the round boom it took many hours to line it up.
And in the end to find that the 9m long 15 element  Yagi was out-performed by the 1m25 3 bander having just 2 element 4 6m   That was quite a deception.
Some HAMs  use this 7/8 6/4m combi say it works well  but compared to what? a dummy perhaps ?







    

1 comment:

PE4BAS, Bas said...

Hallo Jaap, het staat er een beetje omgekeerd maar ik denk dat de 15 elem. beter was als die combi antenne. Of begrijp ik het nu verkeerd. Hoop dat die 4m beam het goed gaat doen straks. Kom ik op je party, maar hoef geen bier!!. 73, Bas

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